[InstCombine] refactor add narrowing folds; NFCI

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.

llvm-svn: 342278

1 files changed, 43 insertions, 71 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 73328666c09..c0fd14b2644 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1032,6 +1032,47 @@ 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.
+  bool WillNotOverflow = IsSext ? willNotOverflowSignedAdd(X, Y, I)
+                                : willNotOverflowUnsignedAdd(X, Y, I);
+  if (!WillNotOverflow)
+    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(),
@@ -1191,77 +1232,8 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
     }
   }
 
-  // Check for (add (sext x), y), see if we can merge this into an
-  // integer add followed by a sext.
-  if (SExtInst *LHSConv = dyn_cast<SExtInst>(LHS)) {
-    // (add (sext x), cst) --> (sext (add x, cst'))
-    if (auto *RHSC = dyn_cast<Constant>(RHS)) {
-      if (LHSConv->hasOneUse()) {
-        Constant *CI =
-            ConstantExpr::getTrunc(RHSC, LHSConv->getOperand(0)->getType());
-        if (ConstantExpr::getSExt(CI, Ty) == RHSC &&
-            willNotOverflowSignedAdd(LHSConv->getOperand(0), CI, I)) {
-          // Insert the new, smaller add.
-          Value *NewAdd =
-              Builder.CreateNSWAdd(LHSConv->getOperand(0), CI, "addconv");
-          return new SExtInst(NewAdd, Ty);
-        }
-      }
-    }
-
-    // (add (sext x), (sext y)) --> (sext (add int x, y))
-    if (SExtInst *RHSConv = dyn_cast<SExtInst>(RHS)) {
-      // Only do this if x/y have the same type, if at least one of them has a
-      // single use (so we don't increase the number of sexts), and if the
-      // integer add will not overflow.
-      if (LHSConv->getOperand(0)->getType() ==
-              RHSConv->getOperand(0)->getType() &&
-          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
-          willNotOverflowSignedAdd(LHSConv->getOperand(0),
-                                   RHSConv->getOperand(0), I)) {
-        // Insert the new integer add.
-        Value *NewAdd = Builder.CreateNSWAdd(LHSConv->getOperand(0),
-                                             RHSConv->getOperand(0), "addconv");
-        return new SExtInst(NewAdd, Ty);
-      }
-    }
-  }
-
-  // Check for (add (zext x), y), see if we can merge this into an
-  // integer add followed by a zext.
-  if (auto *LHSConv = dyn_cast<ZExtInst>(LHS)) {
-    // (add (zext x), cst) --> (zext (add x, cst'))
-    if (auto *RHSC = dyn_cast<Constant>(RHS)) {
-      if (LHSConv->hasOneUse()) {
-        Constant *CI =
-            ConstantExpr::getTrunc(RHSC, LHSConv->getOperand(0)->getType());
-        if (ConstantExpr::getZExt(CI, Ty) == RHSC &&
-            willNotOverflowUnsignedAdd(LHSConv->getOperand(0), CI, I)) {
-          // Insert the new, smaller add.
-          Value *NewAdd =
-              Builder.CreateNUWAdd(LHSConv->getOperand(0), CI, "addconv");
-          return new ZExtInst(NewAdd, Ty);
-        }
-      }
-    }
-
-    // (add (zext x), (zext y)) --> (zext (add int x, y))
-    if (auto *RHSConv = dyn_cast<ZExtInst>(RHS)) {
-      // Only do this if x/y have the same type, if at least one of them has a
-      // single use (so we don't increase the number of zexts), and if the
-      // integer add will not overflow.
-      if (LHSConv->getOperand(0)->getType() ==
-              RHSConv->getOperand(0)->getType() &&
-          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
-          willNotOverflowUnsignedAdd(LHSConv->getOperand(0),
-                                     RHSConv->getOperand(0), I)) {
-        // Insert the new integer add.
-        Value *NewAdd = Builder.CreateNUWAdd(
-            LHSConv->getOperand(0), RHSConv->getOperand(0), "addconv");
-        return new ZExtInst(NewAdd, Ty);
-      }
-    }
-  }
+  if (Instruction *Ext = narrowAddIfNoOverflow(I))
+    return Ext;
 
   // (add (xor A, B) (and A, B)) --> (or A, B)
   // (add (and A, B) (xor A, B)) --> (or A, B)