commit 01511192b23f531b8d378fa522d46647ce7b41a7
author David Bolvansky <david.bolvansky@gmail.com> Thu Jun 20 17:04:14 2019 +0000
committer David Bolvansky <david.bolvansky@gmail.com> Thu Jun 20 17:04:14 2019 +0000
tree 8f38f9e83a88570ecc9d444275729eb96e2915b4
parent 5dbe4a99266393008aaff354f45b977afaecc3c8

[InstCombine] cttz(-x) -> cttz(x)

Summary: Signedness does not change number of trailing zeros.

Reviewers: spatel, lebedev.ri, nikic

Reviewed By: spatel

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63534

llvm-svn: 363951

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e366c37..4bd1246 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1194,6 +1194,12 @@
     return CallInst::Create(F, {X, II.getArgOperand(1)});
   }
 
+  // cttz(-x) -> cttz(x)
+  if (IsTZ && match(Op0, m_Neg(m_Value(X)))) {
+    II.setOperand(0, X);
+    return ⅈ
+  }
+
   KnownBits Known = IC.computeKnownBits(Op0, 0, &II);
 
   // Create a mask for bits above (ctlz) or below (cttz) the first known one.