InstCombine: Don't turn -(x/INT_MIN) -> x/INT_MIN

It is not safe to negate the smallest signed integer, doing so yields
the same number back.

This fixes PR20186.

llvm-svn: 212164

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 5851625383b..b815936ac42 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -107,6 +107,28 @@ bool Constant::isAllOnesValue() const {
   return false;
 }
 
+bool Constant::isMinSignedValue() const {
+  // Check for INT_MIN integers
+  if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
+    return CI->isMinValue(/*isSigned=*/true);
+
+  // Check for FP which are bitcasted from INT_MIN integers
+  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
+    return CFP->getValueAPF().bitcastToAPInt().isMinSignedValue();
+
+  // Check for constant vectors which are splats of INT_MIN values.
+  if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
+    if (Constant *Splat = CV->getSplatValue())
+      return Splat->isMinSignedValue();
+
+  // Check for constant vectors which are splats of INT_MIN values.
+  if (const ConstantDataVector *CV = dyn_cast<ConstantDataVector>(this))
+    if (Constant *Splat = CV->getSplatValue())
+      return Splat->isMinSignedValue();
+
+  return false;
+}
+
 // Constructor to create a '0' constant of arbitrary type...
 Constant *Constant::getNullValue(Type *Ty) {
   switch (Ty->getTypeID()) {