[InstSimplify] simplify add instruction if two operands are negative

Differential Revision: https://reviews.llvm.org/D49216

llvm-svn: 336881

2 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 061ce8f0bd1..87b1fc5b8ee 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -540,6 +540,10 @@ static Value *SimplifyAddInst(Value *Op0, Value *Op1, bool IsNSW, bool IsNUW,
   if (match(Op1, m_Zero()))
     return Op0;
 
+  // If two operands are negative, return 0.
+  if (isKnownNegation(Op0, Op1))
+    return Constant::getNullValue(Op0->getType());
+
   // X + (Y - X) -> Y
   // (Y - X) + X -> Y
   // Eg: X + -X -> 0
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index bdfd1783236..88ed6562c38 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4511,6 +4511,26 @@ static SelectPatternResult matchMinMax(CmpInst::Predicate Pred,
   return {SPF_UNKNOWN, SPNB_NA, false};
 }
 
+bool llvm::isKnownNegation(const Value *X, const Value *Y) {
+  assert(X && Y && "Invalid operand");
+
+  // X = sub (0, Y)
+  if (match(X, m_Neg(m_Specific(Y))))
+    return true;
+
+  // Y = sub (0, X)
+  if (match(Y, m_Neg(m_Specific(X))))
+    return true;
+
+  // X = sub (A, B), Y = sub (B, A)
+  Value *A, *B;
+  if (match(X, m_Sub(m_Value(A), m_Value(B))) &&
+      match(Y, m_Sub(m_Specific(B), m_Specific(A))))
+    return true;
+
+  return false;
+}
+
 static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,
                                               FastMathFlags FMF,
                                               Value *CmpLHS, Value *CmpRHS,