Remove a instcombine transform that (no longer?) makes sense:

    // C - zext(bool) -> bool ? C - 1 : C
    if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
      if (ZI->getSrcTy()->isIntegerTy(1))
        return SelectInst::Create(ZI->getOperand(0), SubOne(C), C);

This ends up forming sext i1 instructions that codegen to terrible code. e.g.
int blah(_Bool x, _Bool y) {
  return (x - y) + 1;
}
=>
        movzbl  %dil, %eax
        movzbl  %sil, %ecx
        shll    $31, %ecx
        sarl    $31, %ecx
        leal    1(%rax,%rcx), %eax
        ret


Without the rule, llvm now generates:
        movzbl  %sil, %ecx
        movzbl  %dil, %eax
        incl    %eax
        subl    %ecx, %eax
        ret

It also helps with ARM (and pretty much any target that doesn't have a sext i1 :-).

The transformation was done as part of Eli's r75531. He has given the ok to
remove it.

rdar://11748024


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159230 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 26 deletions

diff --git a/test/Transforms/InstCombine/zext-bool-add-sub.ll b/test/Transforms/InstCombine/zext-bool-add-sub.ll
index 11642733ac..78bcedbbc2 100644
--- a/test/Transforms/InstCombine/zext-bool-add-sub.ll
+++ b/test/Transforms/InstCombine/zext-bool-add-sub.ll
@@ -1,29 +1,16 @@
-; RUN: opt < %s -instcombine -S | not grep zext
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; rdar://11748024
 
-define i32 @a(i1 %x) {
+define i32 @a(i1 zeroext %x, i1 zeroext %y) {
 entry:
-        %y = zext i1 %x to i32
-        %res = add i32 %y, 1
-        ret i32 %res
-}
-
-define i32 @b(i1 %x) {
-entry:
-        %y = zext i1 %x to i32
-        %res = add i32 %y, -1
-        ret i32 %res
-}
-
-define i32 @c(i1 %x) {
-entry:
-        %y = zext i1 %x to i32
-        %res = sub i32 0, %y
-        ret i32 %res
-}
-
-define i32 @d(i1 %x) {
-entry:
-        %y = zext i1 %x to i32
-        %res = sub i32 3, %y
-        ret i32 %res
+; CHECK: @a
+; CHECK: [[TMP1:%.*]] = zext i1 %y to i32
+; CHECK: [[TMP2:%.*]] = select i1 %x, i32 2, i32 1
+; CHECK-NEXT: sub i32 [[TMP2]], [[TMP1]]
+  %conv = zext i1 %x to i32
+  %conv3 = zext i1 %y to i32
+  %conv3.neg = sub i32 0, %conv3
+  %sub = add i32 %conv, 1
+  %add = add i32 %sub, %conv3.neg
+  ret i32 %add
 }