commit 4b284783898cacd36a1f2bc8a849278bf3a0d57c
author David Bolvansky <david.bolvansky@gmail.com> Fri Jun 21 15:26:22 2019 +0000
committer David Bolvansky <david.bolvansky@gmail.com> Fri Jun 21 15:26:22 2019 +0000
tree afd421f6b803bfb1467a69f56d8a2200d677a026
parent 000f25a37e76317aa78b0f6dd9283ba41af94591

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

Summary: Signedness does not change number of trailing zeros.

Reviewers: spatel, lebedev.ri, nikic

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D63546

llvm-svn: 364064

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 4bd1246..1b24724 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1194,10 +1194,21 @@
     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
+  if (IsTZ) {
+    // cttz(-x) -> cttz(x)
+    if (match(Op0, m_Neg(m_Value(X)))) {
+      II.setOperand(0, X);
+      return ⅈ
+    }
+
+    // cttz(abs(x)) -> cttz(x)
+    // cttz(nabs(x)) -> cttz(x)
+    Value *Y;
+    SelectPatternFlavor SPF = matchSelectPattern(Op0, X, Y).Flavor;
+    if (SPF == SPF_ABS || SPF == SPF_NABS) {
+      II.setOperand(0, X);
+      return ⅈ
+    }
   }
 
   KnownBits Known = IC.computeKnownBits(Op0, 0, &II);