[InstCombine] Simplify ctlz/cttz with bitreverse
Summary: Fixes PR41273
Reviewers: spatel
Reviewed By: spatel
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60096
llvm-svn: 357521
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e6f7e62..c250679 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1324,12 +1324,20 @@
assert((II.getIntrinsicID() == Intrinsic::cttz ||
II.getIntrinsicID() == Intrinsic::ctlz) &&
"Expected cttz or ctlz intrinsic");
+ bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
Value *Op0 = II.getArgOperand(0);
+ Value *X;
+ // ctlz(bitreverse(x)) -> cttz(x)
+ // cttz(bitreverse(x)) -> ctlz(x)
+ if (match(Op0, m_BitReverse(m_Value(X)))) {
+ Intrinsic::ID ID = IsTZ ? Intrinsic::ctlz : Intrinsic::cttz;
+ Function *F = Intrinsic::getDeclaration(II.getModule(), ID, II.getType());
+ return CallInst::Create(F, {X, II.getArgOperand(1)});
+ }
KnownBits Known = IC.computeKnownBits(Op0, 0, &II);
// Create a mask for bits above (ctlz) or below (cttz) the first known one.
- bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
unsigned PossibleZeros = IsTZ ? Known.countMaxTrailingZeros()
: Known.countMaxLeadingZeros();
unsigned DefiniteZeros = IsTZ ? Known.countMinTrailingZeros()