[InstCombine] Fold icmp eq/ne (and %x, signbit), 0 -> %x s>=/s< 0 earlier

Summary:
To generate simplified IR, make sure fold
```
  (X & signbit) ==/!= 0) -> X s>=/s< 0;
```
is scheduled before fold
```
  ((X << Y) & C) == 0 -> (X & (C >> Y)) == 0.
```

https://rise4fun.com/Alive/fbdh

Reviewers: lebedev.ri, efriedma, spatel, craig.topper

Reviewed By: lebedev.ri

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63026

llvm-svn: 363845

1 files changed, 17 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 0cfd930003a..5493b4a85b3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1626,20 +1626,34 @@ Instruction *InstCombiner::foldICmpAndShift(ICmpInst &Cmp, BinaryOperator *And,
 Instruction *InstCombiner::foldICmpAndConstConst(ICmpInst &Cmp,
                                                  BinaryOperator *And,
                                                  const APInt &C1) {
+  bool isICMP_NE = Cmp.getPredicate() == ICmpInst::ICMP_NE;
+
   // For vectors: icmp ne (and X, 1), 0 --> trunc X to N x i1
   // TODO: We canonicalize to the longer form for scalars because we have
   // better analysis/folds for icmp, and codegen may be better with icmp.
-  if (Cmp.getPredicate() == CmpInst::ICMP_NE && Cmp.getType()->isVectorTy() &&
-      C1.isNullValue() && match(And->getOperand(1), m_One()))
+  if (isICMP_NE && Cmp.getType()->isVectorTy() && C1.isNullValue() &&
+      match(And->getOperand(1), m_One()))
     return new TruncInst(And->getOperand(0), Cmp.getType());
 
   const APInt *C2;
-  if (!match(And->getOperand(1), m_APInt(C2)))
+  Value *X;
+  if (!match(And, m_And(m_Value(X), m_APInt(C2))))
     return nullptr;
 
+  // Don't perform the following transforms if the AND has multiple uses
   if (!And->hasOneUse())
     return nullptr;
 
+  if (Cmp.isEquality() && C1.isNullValue()) {
+    // Restrict this fold to single-use 'and' (PR10267).
+    // Replace (and X, (1 << size(X)-1) != 0) with X s< 0
+    if (C2->isSignMask()) {
+      Constant *Zero = Constant::getNullValue(X->getType());
+      auto NewPred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
+      return new ICmpInst(NewPred, X, Zero);
+    }
+  }
+
   // If the LHS is an 'and' of a truncate and we can widen the and/compare to
   // the input width without changing the value produced, eliminate the cast:
   //
@@ -2788,13 +2802,6 @@ Instruction *InstCombiner::foldICmpBinOpEqualityWithConstant(ICmpInst &Cmp,
       if (!BO->hasOneUse())
         break;
 
-      // Replace (and X, (1 << size(X)-1) != 0) with x s< 0
-      if (BOC->isSignMask()) {
-        Constant *Zero = Constant::getNullValue(BOp0->getType());
-        auto NewPred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
-        return new ICmpInst(NewPred, BOp0, Zero);
-      }
-
       // ((X & ~7) == 0) --> X < 8
       if (C.isNullValue() && (~(*BOC) + 1).isPowerOf2()) {
         Constant *NegBOC = ConstantExpr::getNeg(cast<Constant>(BOp1));