Merging r310190:

------------------------------------------------------------------------
r310190 | ctopper | 2017-08-05 16:34:44 -0700 (Sat, 05 Aug 2017) | 18 lines

[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
------------------------------------------------------------------------

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_50@310293 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86InstrSSE.td b/lib/Target/X86/X86InstrSSE.td
index fe87bbd9947385bf8da9a0ea6ed5e64e0e826327..650e4fc8716cd604dadc1568cf6af0f22126231e 100644 (file)
--- a/lib/Target/X86/X86InstrSSE.td
+++ b/lib/Target/X86/X86InstrSSE.td
@@ -3697,8 +3697,7 @@ let SchedRW = [WriteNop] in {
 // Pause. This "instruction" is encoded as "rep; nop", so even though it
 // was introduced with SSE2, it's backward compatible.
 def PAUSE : I<0x90, RawFrm, (outs), (ins),
-              "pause", [(int_x86_sse2_pause)], IIC_SSE_PAUSE>,
-              OBXS, Requires<[HasSSE2]>;
+              "pause", [(int_x86_sse2_pause)], IIC_SSE_PAUSE>, OBXS;
 }
 
 let SchedRW = [WriteFence] in {

diff --git a/test/CodeGen/X86/pause.ll b/test/CodeGen/X86/pause.ll
new file mode 100644 (file)
index 0000000..70ac79f
--- /dev/null
+++ b/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