llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-backend-x86 Author: AZero13 (AZero13) <details> <summary>Changes</summary> The `preserve_none` calling convention is primarily optimized for JIT compilation, hot paths, and avoiding caller-saved registers on non-variadic prototypes. On x86-64, it delegates the 12th integer parameter to the `RAX` register. For variadic functions on the x86-64 System V ABI, the caller is required to set `%al` to the number of vector (XMM) registers being used to pass arguments. Because `preserve_none` delegates unassigned parameters to the standard C calling convention, `LowerCall` will emit an assignment of the XMM register count to `%al`, clobbering the 12th argument passed in `%eax` (the lower 32 bits of `RAX`). Since `preserve_none` fundamentally lacks the register space to pass a 12th argument in `RAX` while simultaneously passing the vector register count in `AL`, this patch explicitly rejects `preserve_none` on variadic functions in both Clang Sema and LLVM's X86 DAG lowering. --- Full diff: https://github.com/llvm/llvm-project/pull/220301.diff 4 Files Affected: - (modified) clang/include/clang/Basic/Specifiers.h (+1) - (modified) clang/test/Sema/preserve-none-call-conv.c (+2) - (modified) llvm/lib/Target/X86/X86ISelLoweringCall.cpp (+10-2) - (added) llvm/test/CodeGen/X86/preserve_none_vararg.ll (+10) ``````````diff diff --git a/clang/include/clang/Basic/Specifiers.h b/clang/include/clang/Basic/Specifiers.h index c1b7198565f07..fdb13f62f1aa1 100644 --- a/clang/include/clang/Basic/Specifiers.h +++ b/clang/include/clang/Basic/Specifiers.h @@ -328,6 +328,7 @@ namespace clang { case CC_Swift: case CC_SwiftAsync: case CC_M68kRTD: + case CC_PreserveNone: return false; default: return true; diff --git a/clang/test/Sema/preserve-none-call-conv.c b/clang/test/Sema/preserve-none-call-conv.c index fc9463726e3f5..6c2f6245cdd57 100644 --- a/clang/test/Sema/preserve-none-call-conv.c +++ b/clang/test/Sema/preserve-none-call-conv.c @@ -18,3 +18,5 @@ typedef_fun_t typedef_fun_boo; // expected-note {{previous declaration is here}} void __attribute__((preserve_none)) typedef_fun_boo(int x) { } // expected-error {{function declared 'preserve_none' here was previously declared without calling convention}} struct type_test_boo {} __attribute__((preserve_none)); // expected-warning {{'preserve_none' attribute only applies to functions and function pointers}} + +void __attribute__((preserve_none)) variadic_boo(int x, ...) { } // expected-error {{variadic function cannot use 'preserve_none' calling convention}} diff --git a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp index 9a03da14ee10e..7a92badb00e59 100644 --- a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp +++ b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp @@ -1960,7 +1960,10 @@ SDValue X86TargetLowering::LowerFormalArguments( MRI.disableCalleeSavedRegister(Pair.first); } - if (CallingConv::PreserveNone == CallConv) + if (CallingConv::PreserveNone == CallConv) { + if (isVarArg) + errorUnsupported(DAG, dl, + "preserve_none calling convention does not support variadic functions"); for (const ISD::InputArg &In : Ins) { if (In.Flags.isSwiftSelf() || In.Flags.isSwiftAsync() || In.Flags.isSwiftError()) { @@ -1969,6 +1972,7 @@ SDValue X86TargetLowering::LowerFormalArguments( break; } } + } return Chain; } @@ -2777,7 +2781,10 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI, InGlue = Chain.getValue(1); } - if (CallingConv::PreserveNone == CallConv) + if (CallingConv::PreserveNone == CallConv) { + if (isVarArg) + errorUnsupported(DAG, dl, + "preserve_none calling convention does not support variadic functions"); for (const ISD::OutputArg &Out : Outs) { if (Out.Flags.isSwiftSelf() || Out.Flags.isSwiftAsync() || Out.Flags.isSwiftError()) { @@ -2786,6 +2793,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI, break; } } + } // Handle result values, copying them out of physregs into vregs that we // return. diff --git a/llvm/test/CodeGen/X86/preserve_none_vararg.ll b/llvm/test/CodeGen/X86/preserve_none_vararg.ll new file mode 100644 index 0000000000000..508b65ef52946 --- /dev/null +++ b/llvm/test/CodeGen/X86/preserve_none_vararg.ll @@ -0,0 +1,10 @@ +; RUN: not llc -mtriple=x86_64-unknown-unknown < %s 2>&1 | FileCheck %s + +; CHECK: LLVM ERROR: preserve_none calling convention does not support variadic functions + +declare preserve_none void @vararg_func(i32, ...) + +define void @test() { + call preserve_none void (i32, ...) @vararg_func(i32 0) + ret void +} `````````` </details> https://github.com/llvm/llvm-project/pull/220301 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
