Add frontend flag for explicitly setting ccc #66072
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rauhul
added
IRGen
include/swift/AST/IRGenOptions.h
Outdated
| @@ -477,6 +478,9 @@ class IRGenOptions { | |||
| /// function instead of to trap instructions. | |||
| std::string TrapFuncName = ""; | |||
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| /// The calling convention used to perform non-swift calls. | |||
| llvm::CallingConv::ID ExperimentalPlatformCCallingConvention; | |||
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Lets drop the word Experimental.
Adds a new swift-frontend flag to allow users to choose which calling convention is used to make c function calls. This hidden flag is called `-experimental-platform-c-calling-convention`. This behavior is needed to workaround rdar://109431863 (Swift-frontend produces trapping llvm ir for non-trapping sil). The root cause of this issue is that IRGen always emits c function calls with llvm's default C calling convention. However clang may select a different (incompatible) calling convention for the function, eventually resulting--via InstCombine and SimplifyCFG--in a trap instead of the function call. This failure mode is most readily seen with the triple `armv7em-apple-none-macho` when attempting to call functions taking struct arguments. Example unoptimized ir below: ```llvm-ir call void @bar([4 x i32] %17, i32 2), !dbg !109 ... define internal arm_aapcs_vfpcc void @bar( [4 x i32] %bar.coerce, i32 noundef %x) ``` In the future it would be better to use the clang importer or some other tool to determine the calling convention for each function instead of setting the calling convention frontend invocation wide. Note: I don't know for sure whether or not clang should be explicitly annotating these functions with a calling convention instead of aliasing C to mean ARM_AAPCS_VFP for this particular combination of `-target`, `-mfloat-abi`, and `-mcpu`.
- Renames ExperimentalPlatformCCallingConvention to PlatformCCallingConvention. - Removes non-arm calling convention support as this feature is working around a clang bug for some arm triples which we hope to see resolved. - Removes misleading MetaVarName from platform-c-calling-convention argument. - Replaces other uses of LLVM::CallingConv::C with IGM.getOptions().PlatformCCallingConvention().
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@swift-ci please test |
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@swift-ci please smoke test |
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Adds a new swift-frontend flag to allow users to choose which calling convention is used to make c function calls. This hidden flag is called
-experimental-platform-c-calling-convention.This behavior is needed to workaround rdar://109431863 (Swift-frontend produces trapping llvm ir for non-trapping sil). The root cause of this issue is that IRGen always emits c function calls with llvm's default C calling convention. However clang may select a different (incompatible) calling convention for the function, eventually resulting--via InstCombine and SimplifyCFG--in a trap instead of the function call. This failure mode is most readily seen with the triple
armv7em-apple-none-machowhen attempting to call functions taking struct arguments. Example unoptimized ir below:In the future it would be better to use the clang importer or some other tool to determine the calling convention for each function instead of setting the calling convention frontend invocation wide.
Note: I don't know for sure whether or not clang should be explicitly annotating these functions with a calling convention instead of aliasing C to mean ARM_AAPCS_VFP for this particular combination of
-target,-mfloat-abi, and-mcpu.