commit 09311459e3750f9dbd164fe7ea40fd9548571128
author Roman Lebedev <lebedev.ri@gmail.com> Thu Dec 05 15:10:25 2019 +0300
committer Roman Lebedev <lebedev.ri@gmail.com> Thu Dec 05 15:48:29 2019 +0300
tree 86bec5e5f9578c0a3c635d3f92a0bcce12956706
parent 11a9bae8f66986751078501988b4414f24dbe37e

[InstCombine] Extend `0 - (X sdiv C) -> (X sdiv -C)` fold to non-splat vectors

Split off from https://reviews.llvm.org/D68408

llvm/lib/IR/Constants.cpp

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index b5df4ea..7ea5cb8 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -150,6 +150,30 @@
   return false;
 }
 
+bool Constant::isNotOneValue() const {
+  // Check for 1 integers
+  if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
+    return !CI->isOneValue();
+
+  // Check for FP which are bitcasted from 1 integers
+  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
+    return !CFP->getValueAPF().bitcastToAPInt().isOneValue();
+
+  // Check that vectors don't contain 1
+  if (this->getType()->isVectorTy()) {
+    unsigned NumElts = this->getType()->getVectorNumElements();
+    for (unsigned i = 0; i != NumElts; ++i) {
+      Constant *Elt = this->getAggregateElement(i);
+      if (!Elt || !Elt->isNotOneValue())
+        return false;
+    }
+    return true;
+  }
+
+  // It *may* contain 1, we can't tell.
+  return false;
+}
+
 bool Constant::isMinSignedValue() const {
   // Check for INT_MIN integers
   if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 8bc3482..5b71f9d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1896,14 +1896,16 @@
                                   Builder.CreateNot(Y, Y->getName() + ".not"));
 
     // 0 - (X sdiv C)  -> (X sdiv -C)  provided the negation doesn't overflow.
-    // TODO: This could be extended to match arbitrary vector constants.
-    const APInt *DivC;
-    if (match(Op0, m_Zero()) && match(Op1, m_SDiv(m_Value(X), m_APInt(DivC))) &&
-        !DivC->isMinSignedValue() && *DivC != 1) {
-      Constant *NegDivC = ConstantInt::get(I.getType(), -(*DivC));
-      Instruction *BO = BinaryOperator::CreateSDiv(X, NegDivC);
-      BO->setIsExact(cast<BinaryOperator>(Op1)->isExact());
-      return BO;
+    if (match(Op0, m_Zero())) {
+      Constant *Op11C;
+      if (match(Op1, m_SDiv(m_Value(X), m_Constant(Op11C))) &&
+          !Op11C->containsUndefElement() && Op11C->isNotMinSignedValue() &&
+          Op11C->isNotOneValue()) {
+        Instruction *BO =
+            BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(Op11C));
+        BO->setIsExact(cast<BinaryOperator>(Op1)->isExact());
+        return BO;
+      }
     }
 
     // 0 - (X << Y)  -> (-X << Y)   when X is freely negatable.