[InstCombine] refactor mul narrowing folds; NFCI

Similar to rL342278:
The test diffs are all cosmetic due to the change in
value naming, but I'm including that to show that the
new code does perform these folds rather than something
else in instcombine.

D52075 should be able to use this code too rather than
duplicating all of the logic.

llvm-svn: 342292

4 files changed, 60 insertions, 112 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 838ef3a1c6a..acb62b6ad9e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1032,45 +1032,6 @@ static Instruction *canonicalizeLowbitMask(BinaryOperator &I,
   return BinaryOperator::CreateNot(NotMask, I.getName());
 }
 
-/// Try to narrow the width of an 'add' if at least 1 operand is an extend of
-/// of a value. This requires a potentially expensive known bits check to make
-/// sure the narrow op does not overflow.
-Instruction *InstCombiner::narrowAddIfNoOverflow(BinaryOperator &I) {
-  // We need at least one extended operand.
-  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
-  Value *X;
-  bool IsSext = match(LHS, m_SExt(m_Value(X)));
-  if (!IsSext && !match(LHS, m_ZExt(m_Value(X))))
-    return nullptr;
-
-  // If both operands are the same extension from the same source type and we
-  // can eliminate at least one (hasOneUse), this might work.
-  CastInst::CastOps CastOpc = IsSext ? Instruction::SExt : Instruction::ZExt;
-  Value *Y;
-  if (!(match(RHS, m_ZExtOrSExt(m_Value(Y))) && X->getType() == Y->getType() &&
-        cast<Operator>(RHS)->getOpcode() == CastOpc &&
-        (LHS->hasOneUse() || RHS->hasOneUse()))) {
-    // If that did not match, see if the RHS is a constant. Truncating and
-    // extending must produce the same constant.
-    Constant *WideC;
-    if (!LHS->hasOneUse() || !match(RHS, m_Constant(WideC)))
-      return nullptr;
-    Constant *NarrowC = ConstantExpr::getTrunc(WideC, X->getType());
-    if (ConstantExpr::getCast(CastOpc, NarrowC, I.getType()) != WideC)
-      return nullptr;
-    Y = NarrowC;
-  }
-  // Both operands have narrow versions. Last step: the math must not overflow
-  // in the narrow width.
-  if (!willNotOverflowAdd(X, Y, I, IsSext))
-    return nullptr;
-
-  // add (ext X), (ext Y) --> ext (add X, Y)
-  // add (ext X), C --> ext (add X, C')
-  Value *NarrowAdd = Builder.CreateAdd(X, Y, "narrow", !IsSext, IsSext);
-  return CastInst::Create(CastOpc, NarrowAdd, I.getType());
-}
-
 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
   if (Value *V = SimplifyAddInst(I.getOperand(0), I.getOperand(1),
                                  I.hasNoSignedWrap(), I.hasNoUnsignedWrap(),
@@ -1230,7 +1191,7 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
     }
   }
 
-  if (Instruction *Ext = narrowAddIfNoOverflow(I))
+  if (Instruction *Ext = narrowMathIfNoOverflow(I))
     return Ext;
 
   // (add (xor A, B) (and A, B)) --> (or A, B)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 1462660a54d..e5d0ac95eef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -538,13 +538,24 @@ private:
                     : willNotOverflowUnsignedMul(LHS, RHS, CxtI);
   }
 
+  bool willNotOverflow(BinaryOperator::BinaryOps Opcode, const Value *LHS,
+                       const Value *RHS, const Instruction &CxtI,
+                       bool IsSigned) const {
+    switch (Opcode) {
+    case Instruction::Add: return willNotOverflowAdd(LHS, RHS, CxtI, IsSigned);
+    case Instruction::Sub: return willNotOverflowSub(LHS, RHS, CxtI, IsSigned);
+    case Instruction::Mul: return willNotOverflowMul(LHS, RHS, CxtI, IsSigned);
+    default: llvm_unreachable("Unexpected opcode for overflow query");
+    }
+  }
+
   Value *EmitGEPOffset(User *GEP);
   Instruction *scalarizePHI(ExtractElementInst &EI, PHINode *PN);
   Value *EvaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask);
   Instruction *foldCastedBitwiseLogic(BinaryOperator &I);
   Instruction *narrowBinOp(TruncInst &Trunc);
   Instruction *narrowMaskedBinOp(BinaryOperator &And);
-  Instruction *narrowAddIfNoOverflow(BinaryOperator &I);
+  Instruction *narrowMathIfNoOverflow(BinaryOperator &I);
   Instruction *narrowRotate(TruncInst &Trunc);
   Instruction *optimizeBitCastFromPhi(CastInst &CI, PHINode *PN);
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index ee2136357ae..d76351fc6fb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -322,77 +322,8 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
   if (match(Op1, m_LShr(m_Value(X), m_APInt(C))) && *C == C->getBitWidth() - 1)
     return BinaryOperator::CreateAnd(Builder.CreateAShr(X, *C), Op0);
 
-  // Check for (mul (sext x), y), see if we can merge this into an
-  // integer mul followed by a sext.
-  if (SExtInst *Op0Conv = dyn_cast<SExtInst>(Op0)) {
-    // (mul (sext x), cst) --> (sext (mul x, cst'))
-    if (auto *Op1C = dyn_cast<Constant>(Op1)) {
-      if (Op0Conv->hasOneUse()) {
-        Constant *CI =
-            ConstantExpr::getTrunc(Op1C, Op0Conv->getOperand(0)->getType());
-        if (ConstantExpr::getSExt(CI, I.getType()) == Op1C &&
-            willNotOverflowSignedMul(Op0Conv->getOperand(0), CI, I)) {
-          // Insert the new, smaller mul.
-          Value *NewMul =
-              Builder.CreateNSWMul(Op0Conv->getOperand(0), CI, "mulconv");
-          return new SExtInst(NewMul, I.getType());
-        }
-      }
-    }
-
-    // (mul (sext x), (sext y)) --> (sext (mul int x, y))
-    if (SExtInst *Op1Conv = dyn_cast<SExtInst>(Op1)) {
-      // Only do this if x/y have the same type, if at last one of them has a
-      // single use (so we don't increase the number of sexts), and if the
-      // integer mul will not overflow.
-      if (Op0Conv->getOperand(0)->getType() ==
-              Op1Conv->getOperand(0)->getType() &&
-          (Op0Conv->hasOneUse() || Op1Conv->hasOneUse()) &&
-          willNotOverflowSignedMul(Op0Conv->getOperand(0),
-                                   Op1Conv->getOperand(0), I)) {
-        // Insert the new integer mul.
-        Value *NewMul = Builder.CreateNSWMul(
-            Op0Conv->getOperand(0), Op1Conv->getOperand(0), "mulconv");
-        return new SExtInst(NewMul, I.getType());
-      }
-    }
-  }
-
-  // Check for (mul (zext x), y), see if we can merge this into an
-  // integer mul followed by a zext.
-  if (auto *Op0Conv = dyn_cast<ZExtInst>(Op0)) {
-    // (mul (zext x), cst) --> (zext (mul x, cst'))
-    if (auto *Op1C = dyn_cast<Constant>(Op1)) {
-      if (Op0Conv->hasOneUse()) {
-        Constant *CI =
-            ConstantExpr::getTrunc(Op1C, Op0Conv->getOperand(0)->getType());
-        if (ConstantExpr::getZExt(CI, I.getType()) == Op1C &&
-            willNotOverflowUnsignedMul(Op0Conv->getOperand(0), CI, I)) {
-          // Insert the new, smaller mul.
-          Value *NewMul =
-              Builder.CreateNUWMul(Op0Conv->getOperand(0), CI, "mulconv");
-          return new ZExtInst(NewMul, I.getType());
-        }
-      }
-    }
-
-    // (mul (zext x), (zext y)) --> (zext (mul int x, y))
-    if (auto *Op1Conv = dyn_cast<ZExtInst>(Op1)) {
-      // Only do this if x/y have the same type, if at last one of them has a
-      // single use (so we don't increase the number of zexts), and if the
-      // integer mul will not overflow.
-      if (Op0Conv->getOperand(0)->getType() ==
-              Op1Conv->getOperand(0)->getType() &&
-          (Op0Conv->hasOneUse() || Op1Conv->hasOneUse()) &&
-          willNotOverflowUnsignedMul(Op0Conv->getOperand(0),
-                                     Op1Conv->getOperand(0), I)) {
-        // Insert the new integer mul.
-        Value *NewMul = Builder.CreateNUWMul(
-            Op0Conv->getOperand(0), Op1Conv->getOperand(0), "mulconv");
-        return new ZExtInst(NewMul, I.getType());
-      }
-    }
-  }
+  if (Instruction *Ext = narrowMathIfNoOverflow(I))
+    return Ext;
 
   bool Changed = false;
   if (!I.hasNoSignedWrap() && willNotOverflowSignedMul(Op0, Op1, I)) {
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 99874b31912..d29cf935751 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1446,6 +1446,51 @@ Instruction *InstCombiner::foldShuffledBinop(BinaryOperator &Inst) {
   return nullptr;
 }
 
+/// Try to narrow the width of a binop if at least 1 operand is an extend of
+/// of a value. This requires a potentially expensive known bits check to make
+/// sure the narrow op does not overflow.
+Instruction *InstCombiner::narrowMathIfNoOverflow(BinaryOperator &BO) {
+  // We need at least one extended operand.
+  Value *LHS = BO.getOperand(0), *RHS = BO.getOperand(1);
+  Value *X;
+  bool IsSext = match(LHS, m_SExt(m_Value(X)));
+  if (!IsSext && !match(LHS, m_ZExt(m_Value(X))))
+    return nullptr;
+
+  // If both operands are the same extension from the same source type and we
+  // can eliminate at least one (hasOneUse), this might work.
+  CastInst::CastOps CastOpc = IsSext ? Instruction::SExt : Instruction::ZExt;
+  Value *Y;
+  if (!(match(RHS, m_ZExtOrSExt(m_Value(Y))) && X->getType() == Y->getType() &&
+        cast<Operator>(RHS)->getOpcode() == CastOpc &&
+        (LHS->hasOneUse() || RHS->hasOneUse()))) {
+    // If that did not match, see if we have a suitable constant operand.
+    // Truncating and extending must produce the same constant.
+    Constant *WideC;
+    if (!LHS->hasOneUse() || !match(RHS, m_Constant(WideC)))
+      return nullptr;
+    Constant *NarrowC = ConstantExpr::getTrunc(WideC, X->getType());
+    if (ConstantExpr::getCast(CastOpc, NarrowC, BO.getType()) != WideC)
+      return nullptr;
+    Y = NarrowC;
+  }
+  // Both operands have narrow versions. Last step: the math must not overflow
+  // in the narrow width.
+  if (!willNotOverflow(BO.getOpcode(), X, Y, BO, IsSext))
+    return nullptr;
+
+  // bo (ext X), (ext Y) --> ext (bo X, Y)
+  // bo (ext X), C       --> ext (bo X, C')
+  Value *NarrowBO = Builder.CreateBinOp(BO.getOpcode(), X, Y, "narrow");
+  if (auto *NewBinOp = dyn_cast<BinaryOperator>(NarrowBO)) {
+    if (IsSext)
+      NewBinOp->setHasNoSignedWrap();
+    else
+      NewBinOp->setHasNoUnsignedWrap();
+  }
+  return CastInst::Create(CastOpc, NarrowBO, BO.getType());
+}
+
 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
   Type *GEPType = GEP.getType();