[llvm] r221455 - [X86] When commuting SSE immediate blend, make sure that the new blend mask is a valid imm8.

[Andrea Di Biagio]

Author: adibiagio
Date: Thu Nov  6 08:36:45 2014
New Revision: 221455

URL: http://llvm.org/viewvc/llvm-project?rev=221455&view=rev
Log:
[X86] When commuting SSE immediate blend, make sure that the new blend mask is a valid imm8.

Example:
define <4 x i32> @test(<4 x i32> %a, <4 x i32> %b) {
  %shuffle = shufflevector <4 x i32> %a, <4 x i32> %b, <4 x i32> <i32 4, i32 5, i32 6, i32 3>
  ret <4 x i32> %shuffle
}

Before llc (-mattr=+sse4.1), produced the following assembly instruction:
  pblendw $4294967103, %xmm1, %xmm0

After
  pblendw $63, %xmm1, %xmm0

Added:
    llvm/trunk/test/CodeGen/X86/commuted-blend-mask.ll
Modified:
    llvm/trunk/lib/Target/X86/X86InstrInfo.cpp

Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=221455&r1=221454&r2=221455&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Thu Nov  6 08:36:45 2014
@@ -2449,7 +2449,8 @@ X86InstrInfo::commuteInstruction(Machine
     case X86::VPBLENDDYrri:  Mask = 0xFF; break;
     case X86::VPBLENDWYrri:  Mask = 0xFF; break;
     }
-    unsigned Imm = MI->getOperand(3).getImm();
+    // Only the least significant bits of Imm are used.
+    unsigned Imm = MI->getOperand(3).getImm() & Mask;
     if (NewMI) {
       MachineFunction &MF = *MI->getParent()->getParent();
       MI = MF.CloneMachineInstr(MI);

Added: llvm/trunk/test/CodeGen/X86/commuted-blend-mask.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/commuted-blend-mask.ll?rev=221455&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/commuted-blend-mask.ll (added)
+++ llvm/trunk/test/CodeGen/X86/commuted-blend-mask.ll Thu Nov  6 08:36:45 2014
@@ -0,0 +1,13 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -mattr=+sse4.1 < %s | FileCheck %s
+
+; When commuting the operands of a SSE blend, make sure that the resulting blend
+; mask can be encoded as a imm8.
+; Before, when commuting the operands to the shuffle in function @test, the backend
+; produced the following assembly:
+;   pblendw $4294967103, %xmm1, %xmm0
+
+define <4 x i32> @test(<4 x i32> %a, <4 x i32> %b) {
+  ;CHECK: pblendw $63, %xmm1, %xmm0
+  %shuffle = shufflevector <4 x i32> %a, <4 x i32> %b, <4 x i32> <i32 4, i32 5, i32 6, i32 3>
+  ret <4 x i32> %shuffle
+}