From 6174da2299f7f4f8193648d03be2b033ceb27410 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Fri, 16 Sep 2022 09:54:11 -0400
Subject: [PATCH] [InstCombine] reduce code duplication in
 foldICmpMulConstant(); NFC

---
 .../Transforms/InstCombine/InstCombineCompares.cpp | 64 +++++++++++-----------
 1 file changed, 31 insertions(+), 33 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 239cd16..fcb4af8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2053,31 +2053,32 @@ Instruction *InstCombinerImpl::foldICmpOrConstant(ICmpInst &Cmp,
 Instruction *InstCombinerImpl::foldICmpMulConstant(ICmpInst &Cmp,
                                                    BinaryOperator *Mul,
                                                    const APInt &C) {
+  ICmpInst::Predicate Pred = Cmp.getPredicate();
+  Type *MulTy = Mul->getType();
+  Value *X = Mul->getOperand(0);
+
   // If there's no overflow:
   // X * X == 0 --> X == 0
   // X * X != 0 --> X != 0
-  Type *MulTy = Mul->getType();
-  if (Cmp.isEquality() && C.isZero() &&
-      Mul->getOperand(0) == Mul->getOperand(1) &&
+  if (Cmp.isEquality() && C.isZero() && X == Mul->getOperand(1) &&
       (Mul->hasNoUnsignedWrap() || Mul->hasNoSignedWrap()))
-    return new ICmpInst(Cmp.getPredicate(), Mul->getOperand(0),
-                        ConstantInt::getNullValue(MulTy));
+    return new ICmpInst(Pred, X, ConstantInt::getNullValue(MulTy));
 
   const APInt *MulC;
   if (!match(Mul->getOperand(1), m_APInt(MulC)))
     return nullptr;
 
   // If this is a test of the sign bit and the multiply is sign-preserving with
-  // a constant operand, use the multiply LHS operand instead.
-  ICmpInst::Predicate Pred = Cmp.getPredicate();
+  // a constant operand, use the multiply LHS operand instead:
+  // (X * +MulC) < 0 --> X < 0
+  // (X * -MulC) < 0 --> X > 0
   if (isSignTest(Pred, C) && Mul->hasNoSignedWrap()) {
     if (MulC->isNegative())
       Pred = ICmpInst::getSwappedPredicate(Pred);
-    return new ICmpInst(Pred, Mul->getOperand(0),
-                        Constant::getNullValue(Mul->getType()));
+    return new ICmpInst(Pred, X, ConstantInt::getNullValue(MulTy));
   }
 
-  if (MulC->isZero() || !(Mul->hasNoSignedWrap() || Mul->hasNoUnsignedWrap()))
+  if (MulC->isZero() || (!Mul->hasNoSignedWrap() && !Mul->hasNoUnsignedWrap()))
     return nullptr;
 
   // If the multiply does not wrap, try to divide the compare constant by the
@@ -2085,48 +2086,45 @@ Instruction *InstCombinerImpl::foldICmpMulConstant(ICmpInst &Cmp,
   if (Cmp.isEquality()) {
     // (mul nsw X, MulC) == C --> X == C /s MulC
     if (Mul->hasNoSignedWrap() && C.srem(*MulC).isZero()) {
-      Constant *NewC = ConstantInt::get(Mul->getType(), C.sdiv(*MulC));
-      return new ICmpInst(Pred, Mul->getOperand(0), NewC);
+      Constant *NewC = ConstantInt::get(MulTy, C.sdiv(*MulC));
+      return new ICmpInst(Pred, X, NewC);
     }
     // (mul nuw X, MulC) == C --> X == C /u MulC
     if (Mul->hasNoUnsignedWrap() && C.urem(*MulC).isZero()) {
-      Constant *NewC = ConstantInt::get(Mul->getType(), C.udiv(*MulC));
-      return new ICmpInst(Pred, Mul->getOperand(0), NewC);
+      Constant *NewC = ConstantInt::get(MulTy, C.udiv(*MulC));
+      return new ICmpInst(Pred, X, NewC);
     }
   }
 
+  // With a matching no-overflow guarantee, fold the constants:
+  // (X * MulC) < C --> X < (C / MulC)
+  // (X * MulC) > C --> X > (C / MulC)
+  // TODO: Assert that Pred is not equal to SGE, SLE, UGE, ULE?
   Constant *NewC = nullptr;
-
-  // FIXME: Add assert that Pred is not equal to ICMP_SGE, ICMP_SLE,
-  // ICMP_UGE, ICMP_ULE.
-
   if (Mul->hasNoSignedWrap()) {
-    if (MulC->isNegative()) {
-      // MININT / -1 --> overflow.
-      if (C.isMinSignedValue() && MulC->isAllOnes())
-        return nullptr;
+    // MININT / -1 --> overflow.
+    if (C.isMinSignedValue() && MulC->isAllOnes())
+      return nullptr;
+    if (MulC->isNegative())
       Pred = ICmpInst::getSwappedPredicate(Pred);
-    }
+
     if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGE)
       NewC = ConstantInt::get(
-          Mul->getType(),
-          APIntOps::RoundingSDiv(C, *MulC, APInt::Rounding::UP));
+          MulTy, APIntOps::RoundingSDiv(C, *MulC, APInt::Rounding::UP));
     if (Pred == ICmpInst::ICMP_SLE || Pred == ICmpInst::ICMP_SGT)
       NewC = ConstantInt::get(
-          Mul->getType(),
-          APIntOps::RoundingSDiv(C, *MulC, APInt::Rounding::DOWN));
-  } else if (Mul->hasNoUnsignedWrap()) {
+          MulTy, APIntOps::RoundingSDiv(C, *MulC, APInt::Rounding::DOWN));
+  } else {
+    assert(Mul->hasNoUnsignedWrap() && "Expected mul nuw");
     if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_UGE)
       NewC = ConstantInt::get(
-          Mul->getType(),
-          APIntOps::RoundingUDiv(C, *MulC, APInt::Rounding::UP));
+          MulTy, APIntOps::RoundingUDiv(C, *MulC, APInt::Rounding::UP));
     if (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_UGT)
       NewC = ConstantInt::get(
-          Mul->getType(),
-          APIntOps::RoundingUDiv(C, *MulC, APInt::Rounding::DOWN));
+          MulTy, APIntOps::RoundingUDiv(C, *MulC, APInt::Rounding::DOWN));
   }
 
-  return NewC ? new ICmpInst(Pred, Mul->getOperand(0), NewC) : nullptr;
+  return NewC ? new ICmpInst(Pred, X, NewC) : nullptr;
 }
 
 /// Fold icmp (shl 1, Y), C.
-- 
2.7.4