[PATCH] D148420: [InstCombine] Enhance select icmp and folding

[Peixin Qiao via Phabricator via llvm-commits]

peixin updated this revision to Diff 520190.
peixin retitled this revision from "[InstSimplify] Enhance select icmp and simplification" to "[InstCombine] Enhance select icmp and folding".
peixin edited the summary of this revision.
peixin set the repository for this revision to rG LLVM Github Monorepo.
peixin removed subscribers: goldstein.w.n, StephenFan, llvm-commits, hiraditya.
peixin added a comment.

Address the comments from @nikic .


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D148420/new/

https://reviews.llvm.org/D148420

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


Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -583,6 +583,38 @@
   return new ZExtInst(ICmpNeZero, SelType);
 }
 
+/// We want to turn:
+///   (select (icmp eq (and X, C), 0), 0, (shl (nsw/nuw) X, K));
+///   iff C is a mask and the number of its leading zeros is equal to K
+/// into:
+///   shl X, K
+static Value *foldSelectICmpAndAnd(const ICmpInst *Cmp,
+                                   Value *TVal, Value *FVal) {
+  ICmpInst::Predicate Pred;
+  Value *AndVal;
+  if (!match(ICmp, m_ICmp(Pred, m_Value(AndVal), m_Zero())))
+    return nullptr;
+
+  Value *X;
+  const APInt *K;
+  if (Pred != ICmpInst::ICMP_EQ ||
+      !match(AndVal, m_And(m_Specific(X), m_APInt(C))) ||
+      !match(TVal, m_Zero()) ||
+      !match(FVal, m_Shl(m_Value(X), m_APInt(K))))
+    return nullptr;
+
+  if (C->isMask() || (int64_t)C->countLeadingZeros() != K->getSExtValue())
+    return nullptr;
+
+  auto *FI = dyn_cast<Instruction>(FVal);
+  if (!FI)
+    return nullptr;
+
+  FI->setHasNoSignedWrap(false);
+  FI->setHasNoUnsignedWrap(false);
+  return FVal;
+}
+
 /// We want to turn:
 ///   (select (icmp sgt x, C), lshr (X, Y), ashr (X, Y)); iff C s>= -1
 ///   (select (icmp slt x, C), ashr (X, Y), lshr (X, Y)); iff C s>= 0
@@ -1806,10 +1838,14 @@
     }
   }
 
+
   if (Instruction *V =
           foldSelectICmpAndAnd(SI.getType(), ICI, TrueVal, FalseVal, Builder))
     return V;
 
+  if (Value *V = foldSelectICmpAndZeroShl(ICI, TrueVal, FalseVal))
+    return replaceInstUsesWith(SI, V);
+
   if (Instruction *V = foldSelectCtlzToCttz(ICI, TrueVal, FalseVal, Builder))
     return V;
 


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