[SPIR-V] Initialize base classes first (microsoft#5894)

When using an initializer list to initialize a class with base classes,
the base classes should be initialized first, and then used as members
of the child class.

This seems to be something of a niche case, but it is one of the asserts
that are failing for
microsoft#5638.

Author: cassiebeckley

tools/clang/lib/SPIRV/InitListHandler.cpp

@@ -394,7 +394,30 @@ InitListHandler::createInitForStructType(QualType type, SourceLocation srcLoc,
   }
 
   llvm::SmallVector<SpirvInstruction *, 4> fields;
+
+  // Initialize base classes first.
+  llvm::SmallVector<SpirvInstruction *, 4> base_fields;
   const RecordDecl *structDecl = type->getAsStructureType()->getDecl();
+  if (auto *cxxStructDecl = dyn_cast<CXXRecordDecl>(structDecl)) {
+    for (CXXBaseSpecifier base : cxxStructDecl->bases()) {
+      QualType baseType = base.getType();
+      const RecordType *baseStructType = baseType->getAsStructureType();
+      if (baseStructType == nullptr) {
+        continue;
+      }
+      const RecordDecl *baseStructDecl = baseStructType->getDecl();
+      for (const auto *field : baseStructDecl->fields()) {
+        base_fields.push_back(
+            createInitForType(field->getType(), field->getLocation(), range));
+        if (!base_fields.back())
+          return nullptr;
+      }
+      fields.push_back(spvBuilder.createCompositeConstruct(
+          baseType, base_fields, srcLoc, range));
+      base_fields.clear();
+    }
+  }
+
   for (const auto *field : structDecl->fields()) {
     fields.push_back(
         createInitForType(field->getType(), field->getLocation(), range));

tools/clang/test/CodeGenSPIRV/var.init.struct.hlsl

@@ -0,0 +1,106 @@
+// RUN: %dxc -T vs_6_0 -E main -fcgl %s -spirv | FileCheck %s
+
+struct S {
+    int3 a;
+    uint b;
+    float2x2 c;
+};
+
+struct T {
+    // Same fields as S
+    int3 h;
+    uint i;
+    float2x2 j;
+
+    // Additional field
+    bool2 k;
+
+    // Embedded S
+    S l;
+
+    // Similar to S but need some casts
+    float3 m;
+    int n;
+    float2x2 o;
+};
+
+struct O {
+    int x;
+};
+
+struct P {
+    O y;
+    float z;
+};
+
+struct Q : O {
+  float z;
+};
+
+struct W {
+  float4 color;
+};
+
+void main() {
+// CHECK-LABEL: %bb_entry = OpLabel
+
+    // Flat initializer list
+// CHECK:      [[a:%[0-9]+]] = OpCompositeConstruct %v3int %int_1 %int_2 %int_3
+// CHECK-NEXT: [[c0:%[0-9]+]] = OpCompositeConstruct %v2float %float_1 %float_2
+// CHECK-NEXT: [[c1:%[0-9]+]] = OpCompositeConstruct %v2float %float_3 %float_4
+// CHECK-NEXT: [[c:%[0-9]+]] = OpCompositeConstruct %mat2v2float [[c0]] [[c1]]
+// CHECK-NEXT: [[s1:%[0-9]+]] = OpCompositeConstruct %S [[a]] %uint_42 [[c]]
+// CHECK-NEXT: OpStore %s1 [[s1]]
+    S s1 = {1, 2, 3, 42, 1., 2., 3., 4.};
+
+    // Random parentheses
+// CHECK:      [[a:%[0-9]+]] = OpCompositeConstruct %v3int %int_1 %int_2 %int_3
+// CHECK-NEXT: [[c0:%[0-9]+]] = OpCompositeConstruct %v2float %float_1 %float_2
+// CHECK-NEXT: [[c1:%[0-9]+]] = OpCompositeConstruct %v2float %float_3 %float_4
+// CHECK-NEXT: [[c:%[0-9]+]] = OpCompositeConstruct %mat2v2float [[c0]] [[c1]]
+// CHECK-NEXT: [[s2:%[0-9]+]] = OpCompositeConstruct %S [[a]] %uint_42 [[c]]
+// CHECK-NEXT: OpStore %s2 [[s2]]
+    S s2 = {{1, 2}, 3, {{42}, {{1.}}}, {2., {3., 4.}}};
+
+    // Flat initalizer list for nested structs
+// CHECK:      [[y:%[0-9]+]] = OpCompositeConstruct %O %int_1
+// CHECK-NEXT: [[p:%[0-9]+]] = OpCompositeConstruct %P [[y]] %float_2
+// CHECK-NEXT: OpStore %p [[p]]
+    P p = {1, 2.};
+
+    // Initalizer list for struct with inheritance.
+// CHECK:      [[y:%[0-9]+]] = OpCompositeConstruct %O %int_1
+// CHECK-NEXT: [[q:%[0-9]+]] = OpCompositeConstruct %Q [[y]] %float_2
+// CHECK-NEXT: OpStore %q [[q]]
+    Q q = {1, 2.};
+
+    // Mixed case: use struct as a whole, decomposing struct, type casting
+
+// CHECK-NEXT: [[s1_val:%[0-9]+]] = OpLoad %S %s1
+// CHECK-NEXT: [[l:%[0-9]+]] = OpLoad %S %s2
+// CHECK-NEXT: [[s2_val:%[0-9]+]] = OpLoad %S %s2
+// CHECK-NEXT: [[h:%[0-9]+]] = OpCompositeExtract %v3int [[s1_val]] 0
+// CHECK-NEXT: [[i:%[0-9]+]] = OpCompositeExtract %uint [[s1_val]] 1
+// CHECK-NEXT: [[j:%[0-9]+]] = OpCompositeExtract %mat2v2float [[s1_val]] 2
+
+// CHECK-NEXT: [[k:%[0-9]+]] = OpCompositeConstruct %v2bool %true %false
+
+// CHECK-NEXT: [[s2av:%[0-9]+]] = OpCompositeExtract %v3int [[s2_val]] 0
+// CHECK-NEXT: [[s2bv:%[0-9]+]] = OpCompositeExtract %uint [[s2_val]] 1
+// CHECK-NEXT: [[o:%[0-9]+]] = OpCompositeExtract %mat2v2float [[s2_val]] 2
+// CHECK-NEXT: [[m:%[0-9]+]] = OpConvertSToF %v3float [[s2av]]
+// CHECK-NEXT: [[n:%[0-9]+]] = OpBitcast %int [[s2bv]]
+// CHECK-NEXT: [[t:%[0-9]+]] = OpCompositeConstruct %T [[h]] [[i]] [[j]] [[k]] [[l]] [[m]] [[n]] [[o]]
+// CHECK-NEXT: OpStore %t [[t]]
+    T t = {s1,          // Decomposing struct
+           true, false, // constructing field from scalar
+           s2,          // Embedded struct
+           s2           // Decomposing struct + type casting
+          };
+
+    // Using InitListExpr
+// CHECK:        [[int4_zero:%[0-9]+]] = OpCompositeConstruct %v4int %int_0 %int_0 %int_0 %int_0
+// CHECK-NEXT: [[float4_zero:%[0-9]+]] = OpConvertSToF %v4float [[int4_zero]]
+// CHECK-NEXT:             {{%[0-9]+}} = OpCompositeConstruct %W [[float4_zero]]
+    W w = { (0).xxxx };
+}

tools/clang/test/CodeGenSPIRV_Lit/var.init.struct.hlsl

@@ -163,7 +163,6 @@ TEST_F(FileTest, LiteralVecTimesScalar) {
 
 // For variables
 TEST_F(FileTest, VarInitScalarVector) { runFileTest("var.init.hlsl"); }
-TEST_F(FileTest, VarInitStruct) { runFileTest("var.init.struct.hlsl"); }
 TEST_F(FileTest, VarInitArray) { runFileTest("var.init.array.hlsl"); }
 
 TEST_F(FileTest, VarInitCrossStorageClass) {