[InstrSimplify] fold sdiv if two operands are negated and non-overflow

Differential Revision: https://reviews.llvm.org/D49382

llvm-svn: 337642

2 files changed, 17 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index e095e95935b..519d6d67be5 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1081,6 +1081,10 @@ static Value *simplifyRem(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
 /// If not, this returns null.
 static Value *SimplifySDivInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
                                unsigned MaxRecurse) {
+  // If two operands are negated and no signed overflow, return -1.
+  if (isKnownNegation(Op0, Op1, /*NeedNSW=*/true))
+    return Constant::getAllOnesValue(Op0->getType());
+
   return simplifyDiv(Instruction::SDiv, Op0, Op1, Q, MaxRecurse);
 }
 
@@ -1111,7 +1115,7 @@ static Value *SimplifySRemInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
 
   // If the two operands are negated, return 0.
   if (isKnownNegation(Op0, Op1))
-   return ConstantInt::getNullValue(Op0->getType());
+    return ConstantInt::getNullValue(Op0->getType());
 
   return simplifyRem(Instruction::SRem, Op0, Op1, Q, MaxRecurse);
 }
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 054f981bab6..54828e392d4 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4511,21 +4511,25 @@ static SelectPatternResult matchMinMax(CmpInst::Predicate Pred,
   return {SPF_UNKNOWN, SPNB_NA, false};
 }
 
-bool llvm::isKnownNegation(const Value *X, const Value *Y) {
+bool llvm::isKnownNegation(const Value *X, const Value *Y, bool NeedNSW) {
   assert(X && Y && "Invalid operand");
 
-  // X = sub (0, Y)
-  if (match(X, m_Neg(m_Specific(Y))))
+  // X = sub (0, Y) || X = sub nsw (0, Y)
+  if ((!NeedNSW && match(X, m_Sub(m_ZeroInt(), m_Specific(Y)))) ||
+      (NeedNSW && match(X, m_NSWSub(m_ZeroInt(), m_Specific(Y)))))
     return true;
 
-  // Y = sub (0, X)
-  if (match(Y, m_Neg(m_Specific(X))))
+  // Y = sub (0, X) || Y = sub nsw (0, X)
+  if ((!NeedNSW && match(Y, m_Sub(m_ZeroInt(), m_Specific(X)))) ||
+      (NeedNSW && match(Y, m_NSWSub(m_ZeroInt(), m_Specific(X)))))
     return true;
 
-  // X = sub (A, B), Y = sub (B, A)
+  // X = sub (A, B), Y = sub (B, A) || X = sub nsw (A, B), Y = sub nsw (B, A)
   Value *A, *B;
-  return match(X, m_Sub(m_Value(A), m_Value(B))) &&
-         match(Y, m_Sub(m_Specific(B), m_Specific(A)));
+  return (!NeedNSW && (match(X, m_Sub(m_Value(A), m_Value(B))) &&
+                        match(Y, m_Sub(m_Specific(B), m_Specific(A))))) ||
+         (NeedNSW && (match(X, m_NSWSub(m_Value(A), m_Value(B))) &&
+                       match(Y, m_NSWSub(m_Specific(B), m_Specific(A)))));
 }
 
 static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,