[SPIR-V] Remove incorrect assert from Decl mapper (microsoft#5884)

Fixes microsoft#5859

Author: sudonatalie

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -1015,6 +1015,12 @@ SpirvDebugGlobalVariable *DeclResultIdMapper::createDebugGlobalVariable(
 SpirvVariable *
 DeclResultIdMapper::createFileVar(const VarDecl *var,
                                   llvm::Optional<SpirvInstruction *> init) {
+  // In the case of template specialization, the same VarDecl node in the AST
+  // may be traversed more than once.
+  if (astDecls[var].instr != nullptr) {
+    return cast<SpirvVariable>(astDecls[var].instr);
+  }
+
   const auto type = getTypeOrFnRetType(var);
   const auto loc = var->getLocation();
   const auto name = var->getName();
@@ -1025,8 +1031,6 @@ DeclResultIdMapper::createFileVar(const VarDecl *var,
   bool isAlias = false;
   (void)getTypeAndCreateCounterForPotentialAliasVar(var, &isAlias);
   varInstr->setContainsAliasComponent(isAlias);
-
-  assert(astDecls[var].instr == nullptr);
   astDecls[var].instr = varInstr;
 
   createDebugGlobalVariable(varInstr, type, loc, name);

tools/clang/test/CodeGenSPIRV_Lit/partial.template.specialization.hlsl

@@ -0,0 +1,26 @@
+// RUN: %dxc -T cs_6_7 -E main -fcgl %s -spirv | FileCheck %s
+
+// CHECK: %bool_type = OpTypeStruct
+template<bool val>
+struct bool_type
+{
+    static const bool value = val;
+};
+
+template<>
+struct bool_type<false>
+{
+    static const bool value = false;
+};
+
+[numthreads(1, 1, 1)]
+void main(uint3 invocationID : SV_DispatchThreadID)
+{
+// CHECK: OpStore %truthVal %true
+    bool_type<true> trueType;
+    bool truthVal = trueType.value;
+
+// CHECK: OpStore %falseVal %false
+    bool_type<false> falseType;
+    bool falseVal = falseType.value;
+}