[PATCH] D101582: [InstCombine] cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true' (PR50172)

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 created this revision.
xbolva00 added reviewers: RKSimon, spatel.
Herald added a subscriber: hiraditya.
xbolva00 requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Zext doesn't change the number of trailing zeros, so narrow cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.

Proof: https://alive2.llvm.org/ce/z/o2dnjY
Solves https://bugs.llvm.org/show_bug.cgi?id=50172


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101582

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp


Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -424,6 +424,7 @@
          "Expected cttz or ctlz intrinsic");
   bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
   Value *Op0 = II.getArgOperand(0);
+  Value *Op1 = II.getArgOperand(1);
   Value *X;
   // ctlz(bitreverse(x)) -> cttz(x)
   // cttz(bitreverse(x)) -> ctlz(x)
@@ -438,6 +439,15 @@
     if (match(Op0, m_Neg(m_Value(X))))
       return IC.replaceOperand(II, 0, X);
 
+    // Zext doesn't change the number of trailing zeros, so narrow:
+    // cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.
+    if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) && match(Op1, m_One())) {
+      auto *Cttz = IC.Builder.CreateBinaryIntrinsic(Intrinsic::cttz, X,
+                                                     IC.Builder.getTrue());
+      auto *ZextCttz = IC.Builder.CreateZExt(Cttz, II.getType());
+      return IC.replaceInstUsesWith(II, ZextCttz);
+    }
+
     // cttz(abs(x)) -> cttz(x)
     // cttz(nabs(x)) -> cttz(x)
     Value *Y;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D101582.341675.patch
Type: text/x-patch
Size: 1214 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210429/b41568eb/attachment.bin>