Add x86-specific DAG combine to simplify:

 x == -y --> x+y == 0
 x != -y --> x+y != 0

On x86, the generated code goes from
   negl    %esi
   cmpl    %esi, %edi
   je    .LBB0_2
to
   addl    %esi, %edi
   je    .L4

This case is correctly handled for ARM with "cmn".

Patch by Manman Ren.
rdar://11245199
PR12545

llvm-svn: 155739

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/neg_cmp.ll b/llvm/test/CodeGen/X86/neg_cmp.ll
new file mode 100644
index 00000000000..866514ed9a2
--- /dev/null
+++ b/llvm/test/CodeGen/X86/neg_cmp.ll
@@ -0,0 +1,22 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; rdar://11245199
+; PR12545
+define void @f(i32 %x, i32 %y) nounwind uwtable ssp {
+entry:
+; CHECK: f:
+; CHECK-NOT: neg
+; CHECK: add
+  %sub = sub i32 0, %y
+  %cmp = icmp eq i32 %x, %sub
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  tail call void @g() nounwind
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  ret void
+}
+
+declare void @g()