MathExtras: add overflow query for signed-div (#97901)

5221634 (Do not trigger UB during AffineExpr parsing) noticed that
divideCeilSigned and divideFloorSigned would overflow when Numerator =
INT_MIN, and Denominator = -1. This observation has already been made by
DynamicAPInt, and it has code to check this. To avoid checks in multiple
callers, centralize this query in MathExtras, and change
divideCeilSigned/divideFloorSigned to assert on overflow.

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/unittests/Support/MathExtrasTest.cpp b/llvm/unittests/Support/MathExtrasTest.cpp
index a557b61..a1cc609 100644
--- a/llvm/unittests/Support/MathExtrasTest.cpp
+++ b/llvm/unittests/Support/MathExtrasTest.cpp
@@ -523,6 +523,12 @@ TEST(MathExtras, DivideCeil) {
             std::numeric_limits<int64_t>::min() / 2 + 1);
   EXPECT_EQ(divideCeilSigned(std::numeric_limits<int64_t>::min(), 1),
             std::numeric_limits<int64_t>::min());
+
+  // Overflow.
+  EXPECT_TRUE(
+      divideSignedWouldOverflow(std::numeric_limits<int8_t>::min(), -1));
+  EXPECT_TRUE(
+      divideSignedWouldOverflow(std::numeric_limits<int64_t>::min(), -1));
 }
 
 TEST(MathExtras, DivideFloorSigned) {
@@ -544,6 +550,8 @@ TEST(MathExtras, DivideFloorSigned) {
             std::numeric_limits<int64_t>::min() / 2);
   EXPECT_EQ(divideFloorSigned(std::numeric_limits<int64_t>::min(), 1),
             std::numeric_limits<int64_t>::min());
+
+  // Same overflow condition, divideSignedWouldOverflow, applies.
 }
 
 TEST(MathExtras, Mod) {