[InstCombine] canonicalize constant-minus-boolean to select-of-constants
This restores the half of:
https://reviews.llvm.org/rL75531
that was reverted at:
https://reviews.llvm.org/rL159230
For the x86 case mentioned there, we now produce:
leal 1(%rdi), %eax
subl %esi, %eax
We have target hooks to invert this in DAGCombiner (and x86 is enabled) with:
https://reviews.llvm.org/rL296977
https://reviews.llvm.org/rL311731
AArch64 and possibly other targets would probably benefit from enabling those hooks too.
See PR30327:
https://bugs.llvm.org/show_bug.cgi?id=30327#c2
Differential Revision: https://reviews.llvm.org/D40612
llvm-svn: 319964
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index d28d615..6888976 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1520,8 +1520,13 @@
return BinaryOperator::CreateNot(Op1);
if (Constant *C = dyn_cast<Constant>(Op0)) {
+ Value *X;
+ // C - zext(bool) -> bool ? C - 1 : C
+ if (match(Op1, m_ZExt(m_Value(X))) &&
+ X->getType()->getScalarSizeInBits() == 1)
+ return SelectInst::Create(X, SubOne(C), C);
+
// C - ~X == X + (1+C)
- Value *X = nullptr;
if (match(Op1, m_Not(m_Value(X))))
return BinaryOperator::CreateAdd(X, AddOne(C));