Translate function pointer from global variable as pointer, not as declaration (#1608)

This patch helps to avoid invalid SPV generation.

When global variable contains a pointer to a function, translator tries to
translate it as declaration. Then it translates this function the second time
when going through the function list. This leads to double translation
of the same function and to the usage of the same IDs in SPIR-V file.

Author: vmaksimo

lib/SPIRV/SPIRVWriter.cpp

@@ -1683,7 +1683,10 @@ LLVMToSPIRVBase::transValueWithoutDecoration(Value *V, SPIRVBasicBlock *BB,
           }
         }
       }
-      BVarInit = transValue(Init, nullptr);
+      // As global variables define a pointer to their "content" type, we should
+      // translate here only pointer without declaration even if it is a
+      // function pointer.
+      BVarInit = transValue(Init, nullptr, true, FuncTransMode::Pointer);
     }
 
     SPIRVStorageClassKind StorageClass;

test/transcoding/SPV_INTEL_function_pointers/global-function-pointer.ll

@@ -0,0 +1,25 @@
+; RUN: llvm-as < %s | llvm-spirv -spirv-ext=+SPV_INTEL_function_pointers -o %t.spv
+; RUN: llvm-spirv %t.spv -spirv-ext=+SPV_INTEL_function_pointers -to-text -o - | FileCheck %s --check-prefix=CHECK-SPIRV
+; RUN: llvm-spirv -r %t.spv -o - | llvm-dis | FileCheck %s --check-prefix=CHECK-LLVM
+
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-n8:16:32:64"
+target triple = "spir64"
+
+
+; CHECK-SPIRV: Capability FunctionPointersINTEL
+; CHECK-SPIRV: Extension "SPV_INTEL_function_pointers"
+; CHECK-SPIRV: TypeFunction [[#FOO_TY:]] [[#]] [[#]]
+; CHECK-SPIRV: TypePointer [[#FOO_TY_PTR:]] [[#]] [[#FOO_TY]]
+; CHECK-SPIRV: ConstantFunctionPointerINTEL [[#FOO_TY_PTR]] [[#FOO_PTR:]] [[#FOO:]]
+; CHECK-SPIRV: Function [[#]] [[#]] [[#]] [[#FOO_TY]]
+
+; CHECK-LLVM: @two = internal addrspace(1) global i32 (i32, i32)* @_Z4barrii
+; CHECK-LLVM: define spir_func i32 @_Z4barrii(i32 %[[#]], i32 %[[#]])
+
+@two = internal addrspace(1) global i32 (i32, i32)* @_Z4barrii, align 8
+
+; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn writeonly
+define protected spir_func noundef i32 @_Z4barrii(i32 %0, i32 %1) {
+entry:
+  ret i32 1
+}