[InstCombine] Don't divide by zero when evaluating a potential transform

Trivial multiplication by zero may survive the worklist.  We tried to
reassociate the multiplication with a division instruction, causing us
to divide by zero; bail out instead.

This fixes PR24726.

llvm-svn: 246939

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a554e9f..bb3d928 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -95,6 +95,14 @@ static bool IsMultiple(const APInt &C1, const APInt &C2, APInt &Quotient,
   assert(C1.getBitWidth() == C2.getBitWidth() &&
          "Inconsistent width of constants!");
 
+  // Bail if we will divide by zero.
+  if (C2.isMinValue())
+    return false;
+
+  // Bail if we would divide INT_MIN by -1.
+  if (IsSigned && C1.isMinSignedValue() && C2.isAllOnesValue())
+    return false;
+
   APInt Remainder(C1.getBitWidth(), /*Val=*/0ULL, IsSigned);
   if (IsSigned)
     APInt::sdivrem(C1, C2, Quotient, Remainder);