[X86] Enable isel to use the PAUSE instruction even when SSE2 is disabled
Summary:
On older processors this instruction encoding is treated as a NOP.
MSVC doesn't disable intrinsics based on features the way clang/gcc does. Because the PAUSE instruction encoding doesn't crash older processors, some software out there uses these intrinsics without checking for SSE2.
This change also seems to also be consistent with gcc behavior.
Fixes PR34079
Reviewers: RKSimon, zvi
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D36361
llvm-svn: 310190
diff --git a/llvm/test/CodeGen/X86/pause.ll b/llvm/test/CodeGen/X86/pause.ll
new file mode 100644
index 0000000..70ac79f
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pause.ll
@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -disable-peephole -mtriple=i386-apple-darwin -mattr=-sse -show-mc-encoding | FileCheck %s
+; RUN: llc < %s -disable-peephole -mtriple=i386-apple-darwin -mattr=-avx,+sse2 -show-mc-encoding | FileCheck %s
+; RUN: llc < %s -disable-peephole -mtriple=i386-apple-darwin -mattr=+avx2 -show-mc-encoding | FileCheck %s
+; RUN: llc < %s -disable-peephole -mtriple=i386-apple-darwin -mcpu=skx -show-mc-encoding | FileCheck %s
+
+define void @test_x86_sse2_pause() {
+; CHECK-LABEL: test_x86_sse2_pause:
+; CHECK: ## BB#0:
+; CHECK-NEXT: pause ## encoding: [0xf3,0x90]
+; CHECK-NEXT: retl ## encoding: [0xc3]
+ tail call void @llvm.x86.sse2.pause()
+ ret void
+}
+declare void @llvm.x86.sse2.pause() nounwind