[WebAssembly] Make llvm.wasm.throw invokable #128104

aheejin · 2025-02-21T01:36:37Z

llvm.wasm.throw intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, __builtin_wasm_throw, which is lowered down to llvm.wasm.rethrow, is used only within _Unwind_RaiseException, which is an one-liner and thus does not need an invoke: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (_Unwind_RaiseException is called by __cxa_throw, which is generated by the throw C++ keyword)

But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has try-catches or destructors.

This makes llvm.wasm.throw invokable in the backend. To do that, this adds a custom lowering routine to SelectionDAGBuilder::visitInvoke, like we did for llvm.wasm.rethrow.

This does not generate invokes for __builtin_wasm_throw yet, which will be done by a follow-up PR.

Addresses #124710.

`llvm.wasm.throw` intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, `__builtin_wasm_throw`, which is lowered down to `llvm.wasm.rethrow`, is used only within `_Unwind_RaiseException`, which is a one-liner and thus does not need an `invoke`: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (`_Unwind_RaiseException` is called by `__cxa_throw`, which is generated by the `throw` C++ keyword) But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has `try`-`catch`es or destructors. This makes `llvm.wasm.throw` invokable in the backend. To do that, this adds a custom lowering routine to `SelectionDAGBuilder::visitInvoke`, like we did for `llvm.wasm.rethrow`. This does not generate `invoke`s for `__builtin_wasm_throw` yet, which will be done by a follow-up PR. Addresses llvm#124710.

llvmbot · 2025-02-21T01:37:10Z

@llvm/pr-subscribers-backend-webassembly

Author: Heejin Ahn (aheejin)

Changes

llvm.wasm.throw intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, __builtin_wasm_throw, which is lowered down to llvm.wasm.rethrow, is used only within _Unwind_RaiseException, which is a one-liner and thus does not need an invoke: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (_Unwind_RaiseException is called by __cxa_throw, which is generated by the throw C++ keyword)

But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has try-catches or destructors.

This makes llvm.wasm.throw invokable in the backend. To do that, this adds a custom lowering routine to SelectionDAGBuilder::visitInvoke, like we did for llvm.wasm.rethrow.

This does not generate invokes for __builtin_wasm_throw yet, which will be done by a follow-up PR.

Addresses #124710.

Full diff: https://github.com/llvm/llvm-project/pull/128104.diff

4 Files Affected:

(modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+16-3)
(modified) llvm/lib/CodeGen/WasmEHPrepare.cpp (+2-4)
(modified) llvm/lib/IR/Verifier.cpp (+3-1)
(modified) llvm/test/CodeGen/WebAssembly/exception.ll (+26)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 1c58a7f05446c..2b333bd81a570 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3360,10 +3360,23 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
     case Intrinsic::experimental_gc_statepoint:
       LowerStatepoint(cast<GCStatepointInst>(I), EHPadBB);
       break;
+    // wasm_throw, wasm_rethrow: This is usually done in visitTargetIntrinsic,
+    // but this intrinsic is special because it can be invoked, so we manually
+    // lower it to a DAG node here.
+    case Intrinsic::wasm_throw: {
+      SmallVector<SDValue, 8> Ops;
+      Ops.push_back(getControlRoot()); // inchain for the terminator node
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      Ops.push_back(
+          DAG.getTargetConstant(Intrinsic::wasm_throw, getCurSDLoc(),
+                                TLI.getPointerTy(DAG.getDataLayout())));
+      Ops.push_back(getValue(I.getArgOperand(0))); // tag
+      Ops.push_back(getValue(I.getArgOperand(1))); // thrown value
+      SDVTList VTs = DAG.getVTList(ArrayRef<EVT>({MVT::Other})); // outchain
+      DAG.setRoot(DAG.getNode(ISD::INTRINSIC_VOID, getCurSDLoc(), VTs, Ops));
+      break;
+    }
     case Intrinsic::wasm_rethrow: {
-      // This is usually done in visitTargetIntrinsic, but this intrinsic is
-      // special because it can be invoked, so we manually lower it to a DAG
-      // node here.
       SmallVector<SDValue, 8> Ops;
       Ops.push_back(getControlRoot()); // inchain for the terminator node
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
diff --git a/llvm/lib/CodeGen/WasmEHPrepare.cpp b/llvm/lib/CodeGen/WasmEHPrepare.cpp
index d18196b2217f5..fc98f594660bb 100644
--- a/llvm/lib/CodeGen/WasmEHPrepare.cpp
+++ b/llvm/lib/CodeGen/WasmEHPrepare.cpp
@@ -201,10 +201,8 @@ bool WasmEHPrepareImpl::prepareThrows(Function &F) {
   // delete all following instructions within the BB, and delete all the dead
   // children of the BB as well.
   for (User *U : ThrowF->users()) {
-    // A call to @llvm.wasm.throw() is only generated from __cxa_throw()
-    // builtin call within libcxxabi, and cannot be an InvokeInst.
-    auto *ThrowI = cast<CallInst>(U);
-    if (ThrowI->getFunction() != &F)
+    auto *ThrowI = dyn_cast<CallInst>(U);
+    if (!ThrowI || ThrowI->getFunction() != &F)
       continue;
     Changed = true;
     auto *BB = ThrowI->getParent();
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 8432779c107de..0ef4438450ea2 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -5203,10 +5203,12 @@ void Verifier::visitInstruction(Instruction &I) {
                 F->getIntrinsicID() == Intrinsic::experimental_patchpoint ||
                 F->getIntrinsicID() == Intrinsic::fake_use ||
                 F->getIntrinsicID() == Intrinsic::experimental_gc_statepoint ||
+                F->getIntrinsicID() == Intrinsic::wasm_throw ||
                 F->getIntrinsicID() == Intrinsic::wasm_rethrow ||
                 IsAttachedCallOperand(F, CBI, i),
             "Cannot invoke an intrinsic other than donothing, patchpoint, "
-            "statepoint, coro_resume, coro_destroy or clang.arc.attachedcall",
+            "statepoint, coro_resume, coro_destroy, clang.arc.attachedcall or "
+            "wasm.(re)throw",
             &I);
       Check(F->getParent() == &M, "Referencing function in another module!", &I,
             &M, F, F->getParent());
diff --git a/llvm/test/CodeGen/WebAssembly/exception.ll b/llvm/test/CodeGen/WebAssembly/exception.ll
index febab822a6a9e..57d1f37c0039f 100644
--- a/llvm/test/CodeGen/WebAssembly/exception.ll
+++ b/llvm/test/CodeGen/WebAssembly/exception.ll
@@ -566,6 +566,32 @@ unreachable:                                      ; preds = %entry
   unreachable
 }
 
+; This tests whether llvm.wasm.throw intrinsic can invoked and iseled correctly.
+
+; CHECK-LABEL: invoke_throw:
+; CHECK: try_table    (catch __cpp_exception 0)
+; CHECK:   local.get  0
+; CHECK:   throw     __cpp_exception
+; CHECK: end_try_table
+define void @invoke_throw(ptr %p) personality ptr @__gxx_wasm_personality_v0 {
+entry:
+  invoke void @llvm.wasm.throw(i32 0, ptr %p)
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [ptr null]
+  %2 = call ptr @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call ptr @__cxa_begin_catch(ptr %2) #4 [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %catch, %entry
+  ret void
+}
 
 declare void @foo()
 declare void @bar(ptr)

llvmbot · 2025-02-21T01:37:10Z

@llvm/pr-subscribers-llvm-ir

Author: Heejin Ahn (aheejin)

Changes

llvm.wasm.throw intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, __builtin_wasm_throw, which is lowered down to llvm.wasm.rethrow, is used only within _Unwind_RaiseException, which is a one-liner and thus does not need an invoke: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (_Unwind_RaiseException is called by __cxa_throw, which is generated by the throw C++ keyword)

But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has try-catches or destructors.

This makes llvm.wasm.throw invokable in the backend. To do that, this adds a custom lowering routine to SelectionDAGBuilder::visitInvoke, like we did for llvm.wasm.rethrow.

This does not generate invokes for __builtin_wasm_throw yet, which will be done by a follow-up PR.

Addresses #124710.

Full diff: https://github.com/llvm/llvm-project/pull/128104.diff

4 Files Affected:

(modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+16-3)
(modified) llvm/lib/CodeGen/WasmEHPrepare.cpp (+2-4)
(modified) llvm/lib/IR/Verifier.cpp (+3-1)
(modified) llvm/test/CodeGen/WebAssembly/exception.ll (+26)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 1c58a7f05446c..2b333bd81a570 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3360,10 +3360,23 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
     case Intrinsic::experimental_gc_statepoint:
       LowerStatepoint(cast<GCStatepointInst>(I), EHPadBB);
       break;
+    // wasm_throw, wasm_rethrow: This is usually done in visitTargetIntrinsic,
+    // but this intrinsic is special because it can be invoked, so we manually
+    // lower it to a DAG node here.
+    case Intrinsic::wasm_throw: {
+      SmallVector<SDValue, 8> Ops;
+      Ops.push_back(getControlRoot()); // inchain for the terminator node
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      Ops.push_back(
+          DAG.getTargetConstant(Intrinsic::wasm_throw, getCurSDLoc(),
+                                TLI.getPointerTy(DAG.getDataLayout())));
+      Ops.push_back(getValue(I.getArgOperand(0))); // tag
+      Ops.push_back(getValue(I.getArgOperand(1))); // thrown value
+      SDVTList VTs = DAG.getVTList(ArrayRef<EVT>({MVT::Other})); // outchain
+      DAG.setRoot(DAG.getNode(ISD::INTRINSIC_VOID, getCurSDLoc(), VTs, Ops));
+      break;
+    }
     case Intrinsic::wasm_rethrow: {
-      // This is usually done in visitTargetIntrinsic, but this intrinsic is
-      // special because it can be invoked, so we manually lower it to a DAG
-      // node here.
       SmallVector<SDValue, 8> Ops;
       Ops.push_back(getControlRoot()); // inchain for the terminator node
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
diff --git a/llvm/lib/CodeGen/WasmEHPrepare.cpp b/llvm/lib/CodeGen/WasmEHPrepare.cpp
index d18196b2217f5..fc98f594660bb 100644
--- a/llvm/lib/CodeGen/WasmEHPrepare.cpp
+++ b/llvm/lib/CodeGen/WasmEHPrepare.cpp
@@ -201,10 +201,8 @@ bool WasmEHPrepareImpl::prepareThrows(Function &F) {
   // delete all following instructions within the BB, and delete all the dead
   // children of the BB as well.
   for (User *U : ThrowF->users()) {
-    // A call to @llvm.wasm.throw() is only generated from __cxa_throw()
-    // builtin call within libcxxabi, and cannot be an InvokeInst.
-    auto *ThrowI = cast<CallInst>(U);
-    if (ThrowI->getFunction() != &F)
+    auto *ThrowI = dyn_cast<CallInst>(U);
+    if (!ThrowI || ThrowI->getFunction() != &F)
       continue;
     Changed = true;
     auto *BB = ThrowI->getParent();
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 8432779c107de..0ef4438450ea2 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -5203,10 +5203,12 @@ void Verifier::visitInstruction(Instruction &I) {
                 F->getIntrinsicID() == Intrinsic::experimental_patchpoint ||
                 F->getIntrinsicID() == Intrinsic::fake_use ||
                 F->getIntrinsicID() == Intrinsic::experimental_gc_statepoint ||
+                F->getIntrinsicID() == Intrinsic::wasm_throw ||
                 F->getIntrinsicID() == Intrinsic::wasm_rethrow ||
                 IsAttachedCallOperand(F, CBI, i),
             "Cannot invoke an intrinsic other than donothing, patchpoint, "
-            "statepoint, coro_resume, coro_destroy or clang.arc.attachedcall",
+            "statepoint, coro_resume, coro_destroy, clang.arc.attachedcall or "
+            "wasm.(re)throw",
             &I);
       Check(F->getParent() == &M, "Referencing function in another module!", &I,
             &M, F, F->getParent());
diff --git a/llvm/test/CodeGen/WebAssembly/exception.ll b/llvm/test/CodeGen/WebAssembly/exception.ll
index febab822a6a9e..57d1f37c0039f 100644
--- a/llvm/test/CodeGen/WebAssembly/exception.ll
+++ b/llvm/test/CodeGen/WebAssembly/exception.ll
@@ -566,6 +566,32 @@ unreachable:                                      ; preds = %entry
   unreachable
 }
 
+; This tests whether llvm.wasm.throw intrinsic can invoked and iseled correctly.
+
+; CHECK-LABEL: invoke_throw:
+; CHECK: try_table    (catch __cpp_exception 0)
+; CHECK:   local.get  0
+; CHECK:   throw     __cpp_exception
+; CHECK: end_try_table
+define void @invoke_throw(ptr %p) personality ptr @__gxx_wasm_personality_v0 {
+entry:
+  invoke void @llvm.wasm.throw(i32 0, ptr %p)
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [ptr null]
+  %2 = call ptr @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call ptr @__cxa_begin_catch(ptr %2) #4 [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %catch, %entry
+  ret void
+}
 
 declare void @foo()
 declare void @bar(ptr)

llvmbot · 2025-02-21T01:37:10Z

@llvm/pr-subscribers-llvm-selectiondag

Author: Heejin Ahn (aheejin)

Changes

llvm.wasm.throw intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, __builtin_wasm_throw, which is lowered down to llvm.wasm.rethrow, is used only within _Unwind_RaiseException, which is a one-liner and thus does not need an invoke: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (_Unwind_RaiseException is called by __cxa_throw, which is generated by the throw C++ keyword)

But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has try-catches or destructors.

This makes llvm.wasm.throw invokable in the backend. To do that, this adds a custom lowering routine to SelectionDAGBuilder::visitInvoke, like we did for llvm.wasm.rethrow.

This does not generate invokes for __builtin_wasm_throw yet, which will be done by a follow-up PR.

Addresses #124710.

Full diff: https://github.com/llvm/llvm-project/pull/128104.diff

4 Files Affected:

(modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+16-3)
(modified) llvm/lib/CodeGen/WasmEHPrepare.cpp (+2-4)
(modified) llvm/lib/IR/Verifier.cpp (+3-1)
(modified) llvm/test/CodeGen/WebAssembly/exception.ll (+26)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 1c58a7f05446c..2b333bd81a570 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3360,10 +3360,23 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
     case Intrinsic::experimental_gc_statepoint:
       LowerStatepoint(cast<GCStatepointInst>(I), EHPadBB);
       break;
+    // wasm_throw, wasm_rethrow: This is usually done in visitTargetIntrinsic,
+    // but this intrinsic is special because it can be invoked, so we manually
+    // lower it to a DAG node here.
+    case Intrinsic::wasm_throw: {
+      SmallVector<SDValue, 8> Ops;
+      Ops.push_back(getControlRoot()); // inchain for the terminator node
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      Ops.push_back(
+          DAG.getTargetConstant(Intrinsic::wasm_throw, getCurSDLoc(),
+                                TLI.getPointerTy(DAG.getDataLayout())));
+      Ops.push_back(getValue(I.getArgOperand(0))); // tag
+      Ops.push_back(getValue(I.getArgOperand(1))); // thrown value
+      SDVTList VTs = DAG.getVTList(ArrayRef<EVT>({MVT::Other})); // outchain
+      DAG.setRoot(DAG.getNode(ISD::INTRINSIC_VOID, getCurSDLoc(), VTs, Ops));
+      break;
+    }
     case Intrinsic::wasm_rethrow: {
-      // This is usually done in visitTargetIntrinsic, but this intrinsic is
-      // special because it can be invoked, so we manually lower it to a DAG
-      // node here.
       SmallVector<SDValue, 8> Ops;
       Ops.push_back(getControlRoot()); // inchain for the terminator node
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
diff --git a/llvm/lib/CodeGen/WasmEHPrepare.cpp b/llvm/lib/CodeGen/WasmEHPrepare.cpp
index d18196b2217f5..fc98f594660bb 100644
--- a/llvm/lib/CodeGen/WasmEHPrepare.cpp
+++ b/llvm/lib/CodeGen/WasmEHPrepare.cpp
@@ -201,10 +201,8 @@ bool WasmEHPrepareImpl::prepareThrows(Function &F) {
   // delete all following instructions within the BB, and delete all the dead
   // children of the BB as well.
   for (User *U : ThrowF->users()) {
-    // A call to @llvm.wasm.throw() is only generated from __cxa_throw()
-    // builtin call within libcxxabi, and cannot be an InvokeInst.
-    auto *ThrowI = cast<CallInst>(U);
-    if (ThrowI->getFunction() != &F)
+    auto *ThrowI = dyn_cast<CallInst>(U);
+    if (!ThrowI || ThrowI->getFunction() != &F)
       continue;
     Changed = true;
     auto *BB = ThrowI->getParent();
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 8432779c107de..0ef4438450ea2 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -5203,10 +5203,12 @@ void Verifier::visitInstruction(Instruction &I) {
                 F->getIntrinsicID() == Intrinsic::experimental_patchpoint ||
                 F->getIntrinsicID() == Intrinsic::fake_use ||
                 F->getIntrinsicID() == Intrinsic::experimental_gc_statepoint ||
+                F->getIntrinsicID() == Intrinsic::wasm_throw ||
                 F->getIntrinsicID() == Intrinsic::wasm_rethrow ||
                 IsAttachedCallOperand(F, CBI, i),
             "Cannot invoke an intrinsic other than donothing, patchpoint, "
-            "statepoint, coro_resume, coro_destroy or clang.arc.attachedcall",
+            "statepoint, coro_resume, coro_destroy, clang.arc.attachedcall or "
+            "wasm.(re)throw",
             &I);
       Check(F->getParent() == &M, "Referencing function in another module!", &I,
             &M, F, F->getParent());
diff --git a/llvm/test/CodeGen/WebAssembly/exception.ll b/llvm/test/CodeGen/WebAssembly/exception.ll
index febab822a6a9e..57d1f37c0039f 100644
--- a/llvm/test/CodeGen/WebAssembly/exception.ll
+++ b/llvm/test/CodeGen/WebAssembly/exception.ll
@@ -566,6 +566,32 @@ unreachable:                                      ; preds = %entry
   unreachable
 }
 
+; This tests whether llvm.wasm.throw intrinsic can invoked and iseled correctly.
+
+; CHECK-LABEL: invoke_throw:
+; CHECK: try_table    (catch __cpp_exception 0)
+; CHECK:   local.get  0
+; CHECK:   throw     __cpp_exception
+; CHECK: end_try_table
+define void @invoke_throw(ptr %p) personality ptr @__gxx_wasm_personality_v0 {
+entry:
+  invoke void @llvm.wasm.throw(i32 0, ptr %p)
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [ptr null]
+  %2 = call ptr @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call ptr @__cxa_begin_catch(ptr %2) #4 [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %catch, %entry
+  ret void
+}
 
 declare void @foo()
 declare void @bar(ptr)

Even though `__builtin_wasm_throw`, which is lowered down to `llvm.wasm.throw`, throws, ```cpp try { __builtin_wasm_throw(0, obj); } catch (...) { } ``` does not generate `invoke`. This is because we have assumed the intrinsic cannot be invoked, which doesn't make much sense. (See llvm#128104 for the historical context) llvm#128104 made `llvm.wasm.throw` intrinsic invokable in the backend. This actually generates `invoke`s in Clang for `__builtin_wasm_throw`. While we're at it, this also generates `invoke`s for `__builtin_wasm_rethrow`, which is actually not used anywhere in C++ support. I haven't deleted it just in case in may have uses later. (For example, to support rethrow functionality that carries stack trace with exnref) Depends on llvm#128104 for the CI to pass. Fixes llvm#124710.

github-actions · 2025-02-21T01:39:54Z

✅ With the latest revision this PR passed the C/C++ code formatter.

arsenm · 2025-02-21T01:41:21Z

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

+      SmallVector<SDValue, 8> Ops;
+      Ops.push_back(getControlRoot()); // inchain for the terminator node
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      Ops.push_back(
+          DAG.getTargetConstant(Intrinsic::wasm_throw, getCurSDLoc(),
+                                TLI.getPointerTy(DAG.getDataLayout())));
+      Ops.push_back(getValue(I.getArgOperand(0))); // tag
+      Ops.push_back(getValue(I.getArgOperand(1))); // thrown value


Can replace opts with a static sized, initialized array

Done: aa5fafd

arsenm · 2025-02-21T01:47:48Z

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-      Ops.push_back(
+      SmallVector<SDValue, 8> Ops = {


Done: aa7b0f6

aheejin · 2025-02-21T02:12:47Z

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

+      std::array<SDValue, 2> Ops = {
+          getControlRoot(), // inchain for the terminator node
          DAG.getTargetConstant(Intrinsic::wasm_rethrow, getCurSDLoc(),
-                                TLI.getPointerTy(DAG.getDataLayout())));
+                                TLI.getPointerTy(DAG.getDataLayout()))};


This just makes the existing wasm_rethrow use std::array and NFC

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

Co-authored-by: Derek Schuff <[email protected]>

Even though `__builtin_wasm_throw`, which is lowered down to `llvm.wasm.throw`, throws, ```cpp try { __builtin_wasm_throw(0, obj); } catch (...) { } ``` does not generate `invoke`. This is because we have assumed the intrinsic cannot be invoked, which doesn't make much sense. (See #128104 for the historical context) #128104 made `llvm.wasm.throw` intrinsic invokable in the backend. This actually generates `invoke`s in Clang for `__builtin_wasm_throw`. While we're at it, this also generates `invoke`s for `__builtin_wasm_rethrow`, which is actually not used anywhere in C++ support. I haven't deleted it just in case in may have uses later. (For example, to support rethrow functionality that carries stack trace with exnref) Depends on #128104 for the CI to pass. Fixes #124710.

purplesyringa · 2025-07-15T12:12:01Z

Hi, I'm confused. This patch is not on any release branch, and it's absent from both LLVM 20.1.0, which released two weeks after this landed, and all the next versions as well. Is this by design?

workingjubilee · 2025-07-15T16:11:25Z

It seems it is part of LLVM 22 currently: https://github.com/llvm/llvm-project/releases/tag/llvmorg-22-init

tgross35 · 2025-07-16T07:25:16Z

Hi, I'm confused. This patch is not on any release branch, and it's absent from both LLVM 20.1.0, which released two weeks after this landed, and all the next versions as well. Is this by design?

It's on the new release/21.x, which forked a few hours after your message https://github.com/llvm/llvm-project/commits/release/21.x/

dianqk · 2025-07-16T23:55:50Z

/cherry-pick d2d469e

llvmbot · 2025-07-17T00:01:39Z

Failed to cherry-pick: d2d469e

https://github.com/llvm/llvm-project/actions/runs/16332802773

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request

tgross35 · 2025-07-17T00:10:11Z

@dianqk this is already on the 21.x branch. I think the milestone needs to be 20.x if you're trying to get it into a patch release (not sure if those are still happening)

dianqk · 2025-07-17T00:21:10Z

@dianqk this is already on the 21.x branch. I think the milestone needs to be 20.x if you're trying to get it into a patch release (not sure if those are still happening)

Ah, I see it.

`llvm.wasm.throw` intrinsic can throw but it was not invokable. Not sure what the rationale was when it was first written that way, but I think at least in Emscripten's C++ exception support with the Wasm port of libunwind, `__builtin_wasm_throw`, which is lowered down to `llvm.wasm.rethrow`, is used only within `_Unwind_RaiseException`, which is an one-liner and thus does not need an `invoke`: https://github.com/emscripten-core/emscripten/blob/720e97f76d6f19e0c6a2d6988988cfe23f0517fb/system/lib/libunwind/src/Unwind-wasm.c#L69 (`_Unwind_RaiseException` is called by `__cxa_throw`, which is generated by the `throw` C++ keyword) But this does not address other direct uses of the builtin in C++, whose use I'm not sure about but is not prohibited. Also other language frontends may need to use the builtin in different functions, which has `try`-`catch`es or destructors. This makes `llvm.wasm.throw` invokable in the backend. To do that, this adds a custom lowering routine to `SelectionDAGBuilder::visitInvoke`, like we did for `llvm.wasm.rethrow`. This does not generate `invoke`s for `__builtin_wasm_throw` yet, which will be done by a follow-up PR. Addresses llvm#124710. (cherry picked from commit d2d469e)

aheejin requested a review from dschuff February 21, 2025 01:36

llvmbot added backend:WebAssembly llvm:SelectionDAG SelectionDAGISel as well llvm:ir labels Feb 21, 2025

aheejin mentioned this pull request Feb 21, 2025

[WebAssembly] Generate invokes with llvm.wasm.(re)throw #128105

Merged

clang-format insists this :(

87456cc

arsenm reviewed Feb 21, 2025

View reviewed changes

Use a static array

aa5fafd

arsenm reviewed Feb 21, 2025

View reviewed changes

Use std::array (also for wasm_rethrow)

aa7b0f6

aheejin commented Feb 21, 2025

View reviewed changes

Error message update in test

614293e

dschuff approved these changes Feb 24, 2025

View reviewed changes

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Outdated Show resolved Hide resolved

aheejin and others added 3 commits February 24, 2025 23:57

Update llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

5d9f948

Co-authored-by: Derek Schuff <[email protected]>

Merge branch 'main' into invokable_throw

722d689

80 col wrapping

f8bd25e

aheejin merged commit d2d469e into llvm:main Feb 25, 2025
11 checks passed

aheejin deleted the invokable_throw branch February 25, 2025 17:53

aheejin mentioned this pull request Feb 26, 2025

llvm.wasm.throw is inconsistently considered non-unwinding or invocable #124710

Closed

purplesyringa mentioned this pull request Jul 15, 2025

WASI unwinding is broken in release rust-lang/rust#132416

Open

dianqk added this to the LLVM 21.x Release milestone Jul 16, 2025

github-project-automation bot added this to LLVM Release Status Jul 16, 2025

github-project-automation bot moved this to Needs Triage in LLVM Release Status Jul 16, 2025

llvmbot added the release:cherry-pick-failed label Jul 17, 2025

dianqk removed this from the LLVM 21.x Release milestone Jul 17, 2025

dianqk mentioned this pull request Jul 17, 2025

Backport #128104 rust-lang/llvm-project#187

Merged

dianqk removed the release:cherry-pick-failed label Jul 17, 2025

[WebAssembly] Make llvm.wasm.throw invokable #128104

[WebAssembly] Make llvm.wasm.throw invokable #128104

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