[llvm-commits] [llvm] r159230 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineAddSub.cpp test/Transforms/InstCombine/mul.ll test/Transforms/InstCombine/zext-bool-add-sub.ll

[Evan Cheng]

Author: evancheng
Date: Tue Jun 26 17:03:13 2012
New Revision: 159230

URL: http://llvm.org/viewvc/llvm-project?rev=159230&view=rev
Log:
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

Added:
    llvm/trunk/test/Transforms/InstCombine/zext-bool-add-sub.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/trunk/test/Transforms/InstCombine/mul.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=159230&r1=159229&r2=159230&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Tue Jun 26 17:03:13 2012
@@ -544,11 +544,6 @@
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
 
-    // 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);
-
     // C-(X+C2) --> (C-C2)-X
     ConstantInt *C2;
     if (match(Op1, m_Add(m_Value(X), m_ConstantInt(C2))))

Modified: llvm/trunk/test/Transforms/InstCombine/mul.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/mul.ll?rev=159230&r1=159229&r2=159230&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/mul.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/mul.ll Tue Jun 26 17:03:13 2012
@@ -138,8 +138,9 @@
         ; e = b & (a >> 31)
         %e = mul i32 %d, %b             ; <i32> [#uses=1]
         ret i32 %e
-; CHECK: [[TEST16:%.*]] = sext i1 %c to i32
-; CHECK-NEXT: %e = and i32 [[TEST16]], %b
+; CHECK: [[TEST16:%.*]] = zext i1 %c to i32
+; CHECK-NEXT: %1 = sub i32 0, [[TEST16]]
+; CHECK-NEXT: %e = and i32 %1, %b
 ; CHECK-NEXT: ret i32 %e
 }
 

Added: llvm/trunk/test/Transforms/InstCombine/zext-bool-add-sub.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/zext-bool-add-sub.ll?rev=159230&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/zext-bool-add-sub.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/zext-bool-add-sub.ll Tue Jun 26 17:03:13 2012
@@ -0,0 +1,16 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; rdar://11748024
+
+define i32 @a(i1 zeroext %x, i1 zeroext %y) {
+entry:
+; 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
+}