[llvm] [mlir] Do not trigger UB during AffineExpr parsing. (PR #96896)

[Adrian Kuegel via llvm-commits]

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@@ -849,10 +859,16 @@ static AffineExpr simplifyFloorDiv(AffineExpr lhs, AffineExpr rhs) {
   if (!rhsConst || rhsConst.getValue() < 1)
     return nullptr;
 
-  if (lhsConst)
+  if (lhsConst) {
+    // divideFloorSigned can only overflow in this case:
+    if (lhsConst.getValue() == std::numeric_limits<int64_t>::min() &&
+        rhsConst.getValue() == -1) {
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akuegel wrote:

Already covered above in line 859

https://github.com/llvm/llvm-project/pull/96896