[spirv] Add support for casting involving vector decomposition

Fixes https://github.com/Microsoft/DirectXShaderCompiler/issues/1673
Fixes https://github.com/Microsoft/DirectXShaderCompiler/issues/1675
Fixes https://github.com/Microsoft/DirectXShaderCompiler/issues/1676

tools/clang/lib/SPIRV/InitListHandler.cpp

@@ -27,7 +27,7 @@ InitListHandler::InitListHandler(const ASTContext &ctx, SPIRVEmitter &emitter)
       spvBuilder(emitter.getSpirvBuilder()),
       diags(emitter.getDiagnosticsEngine()) {}
 
-SpirvInstruction *InitListHandler::process(const InitListExpr *expr) {
+SpirvInstruction *InitListHandler::processInit(const InitListExpr *expr) {
   initializers.clear();
   scalars.clear();
 
@@ -36,7 +36,22 @@ SpirvInstruction *InitListHandler::process(const InitListExpr *expr) {
   // tail of the vector. This is more efficient than using a deque.
   std::reverse(std::begin(initializers), std::end(initializers));
 
-  auto *init = createInitForType(expr->getType(), expr->getExprLoc());
+  return doProcess(expr->getType(), expr->getExprLoc());
+}
+
+SpirvInstruction *InitListHandler::processCast(QualType toType,
+                                               const Expr *expr) {
+  initializers.clear();
+  scalars.clear();
+
+  initializers.push_back(expr);
+
+  return doProcess(toType, expr->getExprLoc());
+}
+
+SpirvInstruction *InitListHandler::doProcess(QualType type,
+                                             SourceLocation srcLoc) {
+  auto *init = createInitForType(type, srcLoc);
 
   if (init) {
     // For successful translation, we should have consumed all initializers and

tools/clang/lib/SPIRV/InitListHandler.h

@@ -83,7 +83,11 @@ public:
 
   /// Processes the given InitListExpr and returns the <result-id> for the final
   /// SPIR-V value.
-  SpirvInstruction *process(const InitListExpr *expr);
+  SpirvInstruction *processInit(const InitListExpr *expr);
+
+  /// Casts the given Expr to the given toType and returns the <result-id> for
+  /// the final SPIR-V value.
+  SpirvInstruction *processCast(QualType toType, const Expr *expr);
 
 private:
   /// \brief Wrapper method to create an error message and report it
@@ -97,7 +101,7 @@ private:
 
   /// Processes the expressions in initializers and returns the <result-id> for
   /// the final SPIR-V value of the given type.
-  uint32_t doProcess(QualType type, SourceLocation srcLoc);
+  SpirvInstruction *doProcess(QualType type, SourceLocation srcLoc);
 
   /// Flattens the given InitListExpr and puts all non-InitListExpr AST nodes
   /// into initializers.

tools/clang/lib/SPIRV/SPIRVEmitter.cpp

@@ -2291,8 +2291,10 @@ SpirvInstruction *SPIRVEmitter::doCastExpr(const CastExpr *expr) {
     // as FlatConversion. For such cases, we can rely on the InitListHandler,
     // which can decompse vectors/matrices.
     else if (subExprType->isArrayType()) {
-      auto valId = InitListHandler(*this).processCast(expr->getType(), subExpr);
-      return SpirvEvalInfo(valId).setRValue();
+      auto *valInstr = InitListHandler(astContext, *this)
+                           .processCast(expr->getType(), subExpr);
+      valInstr->setRValue();
+      return valInstr;
     }
 
     if (!subExprInstr)
@@ -4431,7 +4433,7 @@ SpirvInstruction *SPIRVEmitter::doInitListExpr(const InitListExpr *expr) {
     return id;
   }
 
-  SpirvInstruction *result = InitListHandler(astContext, *this).process(expr);
+  auto *result = InitListHandler(astContext, *this).processInit(expr);
   result->setRValue();
   return result;
 }