DAGCombine add (sext i1), X into sub X, (zext i1) if sext from i1 is illegal. The latter usually compiles into smaller code.

example code:
unsigned foo(unsigned x, unsigned y) {
  if (x != 0) y--;
  return y;
}

before:
  _foo:                           ## @foo
    cmpl  $1, 4(%esp)             ## encoding: [0x83,0x7c,0x24,0x04,0x01]
    sbbl  %eax, %eax              ## encoding: [0x19,0xc0]
    notl  %eax                    ## encoding: [0xf7,0xd0]
    addl  8(%esp), %eax           ## encoding: [0x03,0x44,0x24,0x08]
    ret                           ## encoding: [0xc3]

after:
  _foo:                           ## @foo
    cmpl  $1, 4(%esp)             ## encoding: [0x83,0x7c,0x24,0x04,0x01]
    movl  8(%esp), %eax           ## encoding: [0x8b,0x44,0x24,0x08]
    adcl  $-1, %eax               ## encoding: [0x83,0xd0,0xff]
    ret                           ## encoding: [0xc3]

llvm-svn: 122455

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/add.ll b/llvm/test/CodeGen/X86/add.ll
index d6e99ee1a7e..3ec5358affb 100644
--- a/llvm/test/CodeGen/X86/add.ll
+++ b/llvm/test/CodeGen/X86/add.ll
@@ -120,3 +120,15 @@ entry:
 ; X64: addq
 ; X64-NEXT: sbbq
 ; X64-NEXT: testb
+
+define i32 @test9(i32 %x, i32 %y) nounwind readnone {
+  %cmp = icmp eq i32 %x, 10
+  %sub = sext i1 %cmp to i32
+  %cond = add i32 %sub, %y
+  ret i32 %cond
+; X64: test9:
+; X64: cmpl $10
+; X64: sete
+; X64: subl
+; X64: ret
+}