[UBSan] Cannot negate smallest negative signed integer

[ctetreau]

Summary

Silence warning Undefined Behavior Sanitzer warning:
runtime error: negation of -9223372036854775808 cannot be represented in type 'int64_t' (aka 'long'); cast to an unsigned type to negate this value to itself

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (CTVal && CFVal && CTVal->isAllOnesValue() && CFVal->isNullValue()) {
       const int64_t FalseVal = CFVal->getSExtValue();
       bool Swap = false;
 
       // If both TVal and FVal are constants, see if FVal is the
       // inverse/negation/increment of TVal and generate a CSINV/CSNEG/CSINC
       // instead of a CSEL in that case.
       if (TrueVal == ~FalseVal) {
         Opcode = AArch64ISD::CSINV;
-      } else if (TrueVal == -FalseVal) {
+      } else if (FalseVal > std::numeric_limits<int64_t>::min() &&
+                 TrueVal == -FalseVal) {
         Opcode = AArch64ISD::CSNEG;
       } else if (TVal.getValueType() == MVT::i32) {
         // If our operands are only 32-bit wide, make sure we use 32-bit
         // arithmetic for the check whether we can use CSINC. This ensures that
         // the addition in the check will wrap around properly in case there is
         // an overflow (which would not be the case if we do the check with
         // 64-bit arithmetic).
         const uint32_t TrueVal32 = CTVal->getZExtValue();