Fix assertion when compiling array of struct init (microsoft#6814)

In CGHLSLMSFinishCodeGen's BuildImmInit, when initializing an array, if
the init value type doesn't match the array element type, we must bail
and instead, have it inject a call to the global ctor. Without this,
builds with asserts enabled would assert later with "Wrong type in array
element initializer". In non-assert builds, this invalid IR would be
removed, and valid code emitted.

See microsoft#5294

Author: amaiorano

tools/clang/lib/CodeGen/CGHLSLMSFinishCodeGen.cpp

@@ -2966,7 +2966,6 @@ bool BuildImmInit(Function *Ctor) {
         allConst = false;
         break;
       }
-      ImmList.emplace_back(cast<Constant>(V));
       Value *Ptr = SI->getPointerOperand();
       if (GEPOperator *GepOp = dyn_cast<GEPOperator>(Ptr)) {
         Ptr = GepOp->getPointerOperand();
@@ -2978,6 +2977,15 @@ bool BuildImmInit(Function *Ctor) {
           }
         }
       }
+      // If initializing an array, make sure init value type matches array
+      // element type
+      llvm::Type *GVElemTy = GV->getType()->getElementType();
+      if (llvm::ArrayType *AT = dyn_cast<llvm::ArrayType>(GVElemTy)) {
+        llvm::Type *ElTy = AT->getElementType();
+        if (V->getType() != ElTy)
+          return false;
+      }
+      ImmList.emplace_back(cast<Constant>(V));
     } else {
       if (!isa<ReturnInst>(*I)) {
         allConst = false;

tools/clang/test/DXC/FinishCodeGen/construct-global-array-of-struct.hlsl

@@ -0,0 +1,43 @@
+// RUN: %dxc -T cs_6_0 %s -fcgl | FileCheck %s
+
+// Compiling this HLSL used to trigger this assert:
+//    
+//    Error: assert(V[i]->getType() == Ty->getElementType() && "Wrong type in array element initializer")
+//    File:
+//    ..\..\third_party\dawn\third_party\dxc\lib\IR\Constants.cpp(886)
+//    Func:   static llvm::ConstantArray::getImpl
+//
+// Reported in https://github.com/microsoft/DirectXShaderCompiler/issues/5294
+//
+// Bug was fixed in CGHLSLMSFinishCodeGen in BuildImmInit: when initializing an array,
+// if the init value type doesn't match the array element type, bail. We check that
+// a call to the global ctor function is called.
+
+// CHECK:      define internal void @"\01??__EP@@YAXXZ"() #1 {
+// CHECK:        store i32 0, i32* getelementptr inbounds ([4 x %struct.str], [4 x %struct.str]* @P, i32 0, i32 0, i32 0)
+// CHECK-NEXT:   store i32 0, i32* getelementptr inbounds ([4 x %struct.str], [4 x %struct.str]* @P, i32 0, i32 1, i32 0)
+// CHECK-NEXT:   store i32 0, i32* getelementptr inbounds ([4 x %struct.str], [4 x %struct.str]* @P, i32 0, i32 2, i32 0)
+// CHECK-NEXT:   store i32 0, i32* getelementptr inbounds ([4 x %struct.str], [4 x %struct.str]* @P, i32 0, i32 3, i32 0)
+// CHECK-NEXT:   ret void
+// CHECK-NEXT: }
+//
+// CHECK:      define internal void @_GLOBAL__sub_I_construct_global_array_of_struct.hlsl() #1 {
+// CHECK:        call void @"\01??__EP@@YAXXZ"()
+// CHECK-NEXT:   ret void
+// CHECK-NEXT: }
+
+struct str {
+  int i;
+};
+
+str func(inout str pointer) {
+  return pointer;
+}
+
+static str P[4] = (str[4])0;
+
+[numthreads(1, 1, 1)]
+void main() {
+  const str r = func(P[2]);
+  return;
+}