diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -456,6 +456,9 @@
ENUM_CODEGENOPT(SwiftAsyncFramePointer, SwiftAsyncFramePointerKind, 2,
SwiftAsyncFramePointerKind::Always)
+/// Whether to skip RAX setup when passing variable arguments (x86 only).
+CODEGENOPT(SkipRaxSetup, 1, 0)
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3196,6 +3196,10 @@
HelpText<"Disable function outlining (AArch64 only)">;
def mno_ms_bitfields : Flag<["-"], "mno-ms-bitfields">, Group<m_Group>,
HelpText<"Do not set the default structure layout to be compatible with the Microsoft compiler standard">;
+def mskip_rax_setup : Flag<["-"], "mskip-rax-setup">, Group<m_Group>, Flags<[CC1Option]>,
+ HelpText<"Skip setting up RAX register when passing variable arguments (x86 only)">,
+ MarshallingInfoFlag<CodeGenOpts<"SkipRaxSetup">>;
+def mno_skip_rax_setup : Flag<["-"], "mno-skip-rax-setup">, Group<m_Group>, Flags<[CC1Option]>;
def mstackrealign : Flag<["-"], "mstackrealign">, Group<m_Group>, Flags<[CC1Option]>,
HelpText<"Force realign the stack at entry to every function">,
MarshallingInfoFlag<CodeGenOpts<"StackRealignment">>;
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -840,6 +840,8 @@
getCodeGenOpts().StackProtectorGuardOffset);
if (getCodeGenOpts().StackAlignment)
getModule().setOverrideStackAlignment(getCodeGenOpts().StackAlignment);
+ if (getCodeGenOpts().SkipRaxSetup)
+ getModule().addModuleFlag(llvm::Module::Override, "SkipRaxSetup", 1);
getTargetCodeGenInfo().emitTargetMetadata(*this, MangledDeclNames);
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2210,6 +2210,11 @@
CmdArgs.push_back("-x86-asm-syntax=intel");
}
+ if (Arg *A = Args.getLastArg(options::OPT_mskip_rax_setup,
+ options::OPT_mno_skip_rax_setup))
+ if (A->getOption().matches(options::OPT_mskip_rax_setup))
+ CmdArgs.push_back(Args.MakeArgString("-mskip-rax-setup"));
+
// Set flags to support MCU ABI.
if (Args.hasFlag(options::OPT_miamcu, options::OPT_mno_iamcu, false)) {
CmdArgs.push_back("-mfloat-abi");
diff --git a/clang/test/CodeGen/pr23258.c b/clang/test/CodeGen/pr23258.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/pr23258.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=NO-SKIP
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -mskip-rax-setup -emit-llvm %s -o - | FileCheck %s -check-prefix=SKIP
+
+void f() {}
+
+// SKIP: !"SkipRaxSetup", i32 1}
+// NO-SKIP-NOT: "SkipRaxSetup"
diff --git a/clang/test/Driver/x86_features.c b/clang/test/Driver/x86_features.c
--- a/clang/test/Driver/x86_features.c
+++ b/clang/test/Driver/x86_features.c
@@ -5,3 +5,9 @@
// Test that we don't produce an error with -mieee-fp.
// RUN: %clang -### %s -mieee-fp -S 2>&1 | FileCheck --check-prefix=IEEE %s
// IEEE-NOT: error: unknown argument
+
+// RUN: %clang -### %s -mskip-rax-setup -S 2>&1 | FileCheck --check-prefix=SRS %s
+// SRS: "-mskip-rax-setup"
+
+// RUN: %clang -### %s -mno-skip-rax-setup -S 2>&1 | FileCheck --check-prefix=NO-SRS %s
+// NO-SRS-NOT: "-mskip-rax-setup"
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4415,7 +4415,8 @@
}
}
- if (Is64Bit && isVarArg && !IsWin64 && !IsMustTail) {
+ if (Is64Bit && isVarArg && !IsWin64 && !IsMustTail &&
+ (Subtarget.hasSSE1() || !M->getModuleFlag("SkipRaxSetup"))) {
// From AMD64 ABI document:
// For calls that may call functions that use varargs or stdargs
// (prototype-less calls or calls to functions containing ellipsis (...) in
diff --git a/llvm/test/CodeGen/X86/pr23258.ll b/llvm/test/CodeGen/X86/pr23258.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr23258.ll
@@ -0,0 +1,72 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s --check-prefix=HAS-RAX
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+sse | FileCheck %s --check-prefix=HAS-RAX
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=-sse | FileCheck %s --check-prefix=NO-RAX
+
+define void @foo() {
+; HAS-RAX-LABEL: foo:
+; HAS-RAX: # %bb.0:
+; HAS-RAX-NEXT: movl $1, %edi
+; HAS-RAX-NEXT: xorl %eax, %eax
+; HAS-RAX-NEXT: jmp bar@PLT # TAILCALL
+;
+; NO-RAX-LABEL: foo:
+; NO-RAX: # %bb.0:
+; NO-RAX-NEXT: movl $1, %edi
+; NO-RAX-NEXT: jmp bar@PLT # TAILCALL
+ tail call void (i32, ...) @bar(i32 1)
+ ret void
+}
+
+define void @bar(i32, ...) nounwind {
+; HAS-RAX-LABEL: bar:
+; HAS-RAX: # %bb.0:
+; HAS-RAX-NEXT: subq $56, %rsp
+; HAS-RAX-NEXT: movq %rsi, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movq %rdx, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movq %rcx, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movq %r8, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movq %r9, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: testb %al, %al
+; HAS-RAX-NEXT: je .LBB1_2
+; HAS-RAX-NEXT: # %bb.1:
+; HAS-RAX-NEXT: movaps %xmm0, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm1, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm2, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm3, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm4, -{{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm5, (%rsp)
+; HAS-RAX-NEXT: movaps %xmm6, {{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: movaps %xmm7, {{[0-9]+}}(%rsp)
+; HAS-RAX-NEXT: .LBB1_2:
+; HAS-RAX-NEXT: leaq {{[0-9]+}}(%rsp), %rax
+; HAS-RAX-NEXT: movq %rax, 8
+; HAS-RAX-NEXT: leaq -{{[0-9]+}}(%rsp), %rax
+; HAS-RAX-NEXT: movq %rax, 16
+; HAS-RAX-NEXT: movl $8, 0
+; HAS-RAX-NEXT: movl $48, 4
+; HAS-RAX-NEXT: addq $56, %rsp
+; HAS-RAX-NEXT: retq
+;
+; NO-RAX-LABEL: bar:
+; NO-RAX: # %bb.0:
+; NO-RAX-NEXT: movq %rsi, -{{[0-9]+}}(%rsp)
+; NO-RAX-NEXT: movq %rdx, -{{[0-9]+}}(%rsp)
+; NO-RAX-NEXT: movq %rcx, -{{[0-9]+}}(%rsp)
+; NO-RAX-NEXT: movq %r8, -{{[0-9]+}}(%rsp)
+; NO-RAX-NEXT: movq %r9, -{{[0-9]+}}(%rsp)
+; NO-RAX-NEXT: leaq {{[0-9]+}}(%rsp), %rax
+; NO-RAX-NEXT: movq %rax, 8
+; NO-RAX-NEXT: leaq -{{[0-9]+}}(%rsp), %rax
+; NO-RAX-NEXT: movq %rax, 16
+; NO-RAX-NEXT: movl $8, 0
+; NO-RAX-NEXT: movl $48, 4
+; NO-RAX-NEXT: retq
+ call void @llvm.va_start(i8* null)
+ ret void
+}
+
+declare void @llvm.va_start(i8*)
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 4, !"SkipRaxSetup", i32 1}