Avoid duplication of builtin global variables (#2480)

Add logic to emit only one global variable when both SPIRV builtin and OCL builtin variants are present in the source code.

Signed-off-by: Arvind Sudarsanam <arvind.sudarsanam@intel.com>

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@2a247a49eddbc8f

Author: asudarsa

llvm-spirv/lib/SPIRV/SPIRVUtil.cpp

@@ -2142,9 +2142,26 @@ bool lowerBuiltinCallsToVariables(Module *M) {
     bool IsVec = F.getFunctionType()->getNumParams() > 0;
     Type *GVType =
         IsVec ? FixedVectorType::get(F.getReturnType(), 3) : F.getReturnType();
-    auto *BV = new GlobalVariable(
-        *M, GVType, /*isConstant=*/true, GlobalValue::ExternalLinkage, nullptr,
-        BuiltinVarName, 0, GlobalVariable::NotThreadLocal, SPIRAS_Input);
+    GlobalVariable *BV = nullptr;
+    // Consider the following LLVM IR:
+    // @__spirv_BuiltInLocalInvocationId = <Global constant>
+    // .....
+    // define spir_kernel void @kernel1(....) {
+    //   %3 = tail call i64 @_Z12get_local_idj(i32 0)
+    //   .....
+    //   return void
+    // }
+    // During the OCLToSPIRV pass, the opencl call will get lowered to
+    // yet another global variable with the name
+    // '@__spirv_BuiltInLocalInvocationId'. In such a case, we would want to
+    // create only a single global variable with this name.
+    if (GlobalVariable *GV = M->getGlobalVariable(BuiltinVarName))
+      BV = GV;
+    else
+      BV = new GlobalVariable(*M, GVType, /*isConstant=*/true,
+                              GlobalValue::ExternalLinkage, nullptr,
+                              BuiltinVarName, 0, GlobalVariable::NotThreadLocal,
+                              SPIRAS_Input);
     for (auto *U : F.users()) {
       auto *CI = dyn_cast<CallInst>(U);
       assert(CI && "invalid instruction");

llvm-spirv/test/builtin_duplicate.ll

@@ -0,0 +1,33 @@
+;; This test checks if we generate a single builtin variable for the following
+;; LLVM IR.
+;; @__spirv_BuiltInLocalInvocationId - A global variable
+;; %3 = tail call i64 @_Z12get_local_idj(i32 0) - A function call
+
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: llvm-spirv %t.bc -spirv-text -o %t.txt
+; RUN: FileCheck < %t.txt %s --check-prefix=CHECK-SPIRV
+; RUN: spirv-val %t.spv
+
+target datalayout = "e-p:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir-unknown-unknown"
+
+%opencl.event_t = type opaque
+
+; CHECK-SPIRV: {{[0-9]+}} Name {{[0-9]+}} "__spirv_BuiltInLocalInvocationId"
+; CHECK-SPIRV-NOT: {{[0-9]+}} Name {{[0-9]+}} "__spirv_BuiltInLocalInvocationId.1"
+
+@__spirv_BuiltInLocalInvocationId = external dso_local local_unnamed_addr addrspace(1) constant <3 x i64>, align 32
+
+declare spir_func i64 @_Z12get_local_idj(i32) local_unnamed_addr
+
+; Function Attrs: nounwind
+define spir_kernel void @test_fn(i32 %a) {
+entry:
+  %3 = tail call i64 @_Z12get_local_idj(i32 0)
+  ret void
+}
+
+!spirv.Source = !{!0}
+
+!0 = !{i32 6, i32 100000}