X86: optimize generated code for integer ABS

This patch will generate the following for integer ABS:
      movl    %edi, %eax
      negl    %eax
      cmovll  %edi, %eax
INSTEAD OF
      movl    %edi, %ecx
      sarl    $31, %ecx
      leal    (%rdi,%rcx), %eax
      xorl    %ecx, %eax

There exists a target-independent DAG combine for integer ABS, which converts
integer ABS to sar+add+xor. For X86, we match this pattern back to neg+cmov. 
This is implemented in PerformXorCombine.

rdar://10695237

llvm-svn: 158175

1 files changed, 10 insertions, 6 deletions

diff --git a/llvm/test/CodeGen/X86/iabs.ll b/llvm/test/CodeGen/X86/iabs.ll
index a8ba0155fd1..9196cce1ae5 100644
--- a/llvm/test/CodeGen/X86/iabs.ll
+++ b/llvm/test/CodeGen/X86/iabs.ll
@@ -1,13 +1,17 @@
-; RUN: llc < %s -march=x86-64 -stats  |& \
-; RUN:   grep {5 .*Number of machine instrs printed}
+; RUN: llc < %s -march=x86-64 | FileCheck %s
 
 ;; Integer absolute value, should produce something at least as good as:
-;;       movl %edi, %ecx
-;;       sarl $31, %ecx
-;;       leal (%rdi,%rcx), %eax
-;;       xorl %ecx, %eax
+;;       movl   %edi, %eax
+;;       negl   %eax
+;;       cmovll %edi, %eax
 ;;       ret
+; rdar://10695237
 define i32 @test(i32 %a) nounwind {
+; CHECK: test:
+; CHECK: mov
+; CHECK-NEXT: neg
+; CHECK-NEXT: cmov
+; CHECK-NEXT: ret
         %tmp1neg = sub i32 0, %a
         %b = icmp sgt i32 %a, -1
         %abs = select i1 %b, i32 %a, i32 %tmp1neg