[CIR][Lowering][CXXABI]lower var_arg op #570
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| static mlir::Value createGetMemberOp(CIRBaseBuilderTy &builder, | ||
| mlir::Location &loc, mlir::Value structPtr, | ||
| const char *fldName, unsigned idx) { | ||
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| assert(structPtr.getType().isa<mlir::cir::PointerType>()); | ||
| auto structBaseTy = | ||
| structPtr.getType().cast<mlir::cir::PointerType>().getPointee(); | ||
| assert(structBaseTy.isa<mlir::cir::StructType>()); | ||
| auto fldTy = structBaseTy.cast<mlir::cir::StructType>().getMembers()[idx]; | ||
| auto fldPtrTy = ::mlir::cir::PointerType::get(builder.getContext(), fldTy); | ||
| return builder.create<mlir::cir::GetMemberOp>(loc, fldPtrTy, structPtr, | ||
| fldName, idx); | ||
| } |
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Is this function general or is it specific to ARM64 ABI? If it is general you can move it to CIRBaseBuilderTy.
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This is general, will move to CIRBaseBuilderTy
| //====- LoweringPrepareItaniumCXXABI.cpp - Itanium ABI specific code | ||
| //--------===// |
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Please keep these 2 lines of file header in the same line.
| //====- LoweringPrepareItaniumCXXABI.cpp - Itanium ABI specific code | |
| //--------===// | |
| //====- LoweringPrepareItaniumCXXABI.cpp - Itanium ABI specific code ------===// |
| // TODO: implement va_arg for more generic Itanium ABI. | ||
| return mlir::Value(); |
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Maybe an assertion here would be better?
| // TODO: implement va_arg for more generic Itanium ABI. | |
| return mlir::Value(); | |
| llvm_unreachable("NYI"); |
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its needed by clang/lib/CIR/Dialect/Transforms/LoweringPrepareArm64CXXABI.cpp as LoweringPrepareArm64CXXABI inherits from LoweringPrepareItaniumCXXABI
| builder.setInsertionPoint(op); | ||
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| auto res = cxxABI->lowerVAArg(builder, op); | ||
| if (res) { |
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I understand lowerVAArg could never return an empty value so the branching here is unnecessary.
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lowerVAArg returns null from LoweringPrepareItaniumCXXABI. This is the current way of prevent lowering of cir.var_arg if Lowering is not ready for an ABI (e.g. x86_64)
lowering var_arg op for ARM64 architecture. This is CIR lowering.
This PR modified LoweringPrepare CXXABI code to make LoweringPrepareArm64CXXABI class inherit more generic LoweringPrepareItaniumCXXABI, this way lowering var_arg would be only meaningful for arm64 targets and for other arch its no op for now.
The ABI doc and detailed algorithm description can be found in this official doc.
https://github.com/ARM-software/abi-aa/blob/617079d8a0d45bec83d351974849483cf0cc66d5/aapcs64/aapcs64.rst#appendix-variable-argument-lists
The following pic is a easier-to-understand and close to lowered code explaination