[PATCH] D112413: [X86] Add -mskip-rax-setup support to align with GCC

[Phoebe Wang via Phabricator via llvm-commits]

pengfei updated this revision to Diff 381997.
pengfei added a comment.

Address review comment.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D112413/new/

https://reviews.llvm.org/D112413

Files:
  clang/include/clang/Driver/Options.td
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/test/Driver/x86_features.c
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/lib/Target/X86/pr23258.ll


Index: llvm/lib/Target/X86/pr23258.ll
===================================================================
--- /dev/null
+++ llvm/lib/Target/X86/pr23258.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; 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 -x86-skip-rax-setup | FileCheck %s --check-prefix=HAS-RAX
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+sse -x86-skip-rax-setup | FileCheck %s --check-prefix=HAS-RAX
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=-sse -x86-skip-rax-setup | FileCheck %s --check-prefix=NO-RAX
+
+define dso_local void @foo() nounwind {
+; HAS-RAX-LABEL: foo:
+; HAS-RAX:       # %bb.0: # %entry
+; HAS-RAX-NEXT:    movl $1, %edi
+; HAS-RAX-NEXT:    xorl %eax, %eax
+; HAS-RAX-NEXT:    jmp bar # TAILCALL
+;
+; NO-RAX-LABEL: foo:
+; NO-RAX:       # %bb.0: # %entry
+; NO-RAX-NEXT:    movl $1, %edi
+; NO-RAX-NEXT:    jmp bar # TAILCALL
+entry:
+  tail call void (i32, ...) @bar(i32 1)
+  ret void
+}
+
+declare dso_local void @bar(i32, ...)
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -93,6 +93,12 @@
              "stores respectively."),
     cl::Hidden);
 
+static cl::opt<bool> SkipRaxSetup(
+    "x86-skip-rax-setup", cl::init(false),
+    cl::desc("Skips setting up the RAX register when SSE is disabled. This "
+             "option has nothing to do with 32 bits or SSE enabled case."),
+    cl::Hidden);
+
 /// Call this when the user attempts to do something unsupported, like
 /// returning a double without SSE2 enabled on x86_64. This is not fatal, unlike
 /// report_fatal_error, so calling code should attempt to recover without
@@ -4414,7 +4420,8 @@
     }
   }
 
-  if (Is64Bit && isVarArg && !IsWin64 && !IsMustTail) {
+  if (Is64Bit && isVarArg && !IsWin64 && !IsMustTail &&
+      (Subtarget.hasSSE1() || !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
Index: clang/test/Driver/x86_features.c
===================================================================
--- clang/test/Driver/x86_features.c
+++ clang/test/Driver/x86_features.c
@@ -5,3 +5,6 @@
 // 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: "-mllvm" "-x86-skip-rax-setup"
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -2194,6 +2194,11 @@
     CmdArgs.push_back("-x86-asm-syntax=intel");
   }
 
+  if (Args.hasArg(options::OPT_mskip_rax_setup)) {
+    CmdArgs.push_back("-mllvm");
+    CmdArgs.push_back("-x86-skip-rax-setup");
+  }
+
   // Set flags to support MCU ABI.
   if (Args.hasFlag(options::OPT_miamcu, options::OPT_mno_iamcu, false)) {
     CmdArgs.push_back("-mfloat-abi");
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -3189,6 +3189,8 @@
     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<[NoXarchOption]>,
+  HelpText<"Skip setting up RAX register when passing variable arguments (x86 only)">;
 def mstackrealign : Flag<["-"], "mstackrealign">, Group<m_Group>, Flags<[CC1Option]>,
   HelpText<"Force realign the stack at entry to every function">,
   MarshallingInfoFlag<CodeGenOpts<"StackRealignment">>;


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