[SYCL][CUDA] Update code when llvm.used is removed (#4409)

When using `sycl-post-link` llvm.used should be removed. Otherwise it can cause a crash further on. 
This patch checks to see if llvm.used is removed and if it is prevents the old code from being reused in the table.

This fixes #4294. 
See issue for more details on problem.

Author: AidanBeltonS

llvm/test/tools/sycl-post-link/erase_used.ll

@@ -1,9 +1,16 @@
 ; This test checks that the post-link tool does not add "llvm.used" global to
-; the output modules when splitting kernels.
+; the output modules when splitting modules, creating a single row table,
+; and outputing IR only
 ;
 ; RUN: sycl-post-link -split=kernel -S %s -o %t.files.table
 ; RUN: FileCheck %s -input-file=%t.files_0.ll
 ; RUN: FileCheck %s -input-file=%t.files_1.ll
+;
+; RUN: sycl-post-link -S -split=auto -symbols -split-esimd -lower-esimd -O2 -spec-const=default %s -o %t.out.table
+; RUN: FileCheck %s --input-file=%t.out_0.ll
+;
+; RUN: sycl-post-link -S -split=auto -ir-output-only %s -o %t.out_ir_only.ll
+; RUN: FileCheck %s --input-file %t.out_ir_only.ll
 
 target triple = "spir64-unknown-unknown-sycldevice"
 

llvm/tools/sycl-post-link/sycl-post-link.cpp

@@ -714,6 +714,20 @@ static TableFiles processOneModule(std::unique_ptr<Module> M, bool IsEsimd,
   if (!M)
     return TblFiles;
 
+  // After linking device bitcode "llvm.used" holds references to the kernels
+  // that are defined in the device image. But after splitting device image into
+  // separate kernels we may end up with having references to kernel declaration
+  // originating from "llvm.used" in the IR that is passed to llvm-spirv tool,
+  // and these declarations cause an assertion in llvm-spirv. To workaround this
+  // issue remove "llvm.used" from the input module before performing any other
+  // actions.
+  bool IsLLVMUsedRemoved = false;
+  if (GlobalVariable *GV = M->getGlobalVariable("llvm.used")) {
+    assert(GV->user_empty() && "unexpected llvm.used users");
+    GV->eraseFromParent();
+    IsLLVMUsedRemoved = true;
+  }
+
   if (IsEsimd && LowerEsimd)
     LowerEsimdConstructs(*M);
 
@@ -773,7 +787,8 @@ static TableFiles processOneModule(std::unique_ptr<Module> M, bool IsEsimd,
     // no spec constants and no splitting.
     // We cannot reuse input module for ESIMD code since it was transformed.
     bool CanReuseInputModule = !SpecConstsMet && (ResultModules.size() == 1) &&
-                               !SyclAndEsimdCode && !IsEsimd;
+                               !SyclAndEsimdCode && !IsEsimd &&
+                               !IsLLVMUsedRemoved;
     string_vector Files =
         CanReuseInputModule
             ? string_vector{InputFilename}
@@ -981,18 +996,6 @@ int main(int argc, char **argv) {
     return 1;
   }
 
-  // After linking device bitcode "llvm.used" holds references to the kernels
-  // that are defined in the device image. But after splitting device image into
-  // separate kernels we may end up with having references to kernel declaration
-  // originating from "llvm.used" in the IR that is passed to llvm-spirv tool,
-  // and these declarations cause an assertion in llvm-spirv. To workaround this
-  // issue remove "llvm.used" from the input module before performing any other
-  // actions.
-  if (GlobalVariable *GV = MPtr->getGlobalVariable("llvm.used")) {
-    assert(GV->user_empty() && "unexpected llvm.used users");
-    GV->eraseFromParent();
-  }
-
   if (OutputFilename.getNumOccurrences() == 0)
     OutputFilename = (Twine(sys::path::stem(InputFilename)) + ".files").str();