[clang] [CIR] Upstream CastOp and scalar conversions (PR #130690)

[Erich Keane via cfe-commits]

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@@ -247,6 +280,179 @@ struct ConvertCIRToLLVMPass
   StringRef getArgument() const override { return "cir-flat-to-llvm"; }
 };
 
+mlir::Type CIRToLLVMCastOpLowering::convertTy(mlir::Type ty) const {
+  return getTypeConverter()->convertType(ty);
+}
+
+mlir::LogicalResult CIRToLLVMCastOpLowering::matchAndRewrite(
+    cir::CastOp castOp, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  // For arithmetic conversions, LLVM IR uses the same instruction to convert
+  // both individual scalars and entire vectors. This lowering pass handles
+  // both situations.
+
+  switch (castOp.getKind()) {
+  case cir::CastKind::array_to_ptrdecay: {
+    const auto ptrTy = mlir::cast<cir::PointerType>(castOp.getType());
+    auto sourceValue = adaptor.getOperands().front();
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erichkeane wrote:

A LOT of uses of 'auto' in this function that don't match our coding standard.

https://github.com/llvm/llvm-project/pull/130690