[llvm] [AArch64] Check for negative numbers when adjusting icmps (PR #140999)

[via llvm-commits]

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@@ -3760,52 +3770,53 @@ static SDValue getAArch64Cmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
                              const SDLoc &dl) {
   if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS.getNode())) {
     EVT VT = RHS.getValueType();
-    uint64_t C = RHSC->getZExtValue();
-    if (!isLegalArithImmed(C)) {
+    int64_t C = RHSC->getSExtValue();
+    if (!isLegalCmpImmed(C)) {
       // Constant does not fit, try adjusting it by one?
       switch (CC) {
       default:
         break;
       case ISD::SETLT:
       case ISD::SETGE:
-        if ((VT == MVT::i32 && C != 0x80000000 &&
-             isLegalArithImmed((uint32_t)(C - 1))) ||
-            (VT == MVT::i64 && C != 0x80000000ULL &&
-             isLegalArithImmed(C - 1ULL))) {
+        if ((VT == MVT::i32 && C != INT32_MIN && isLegalCmpImmed(C - 1)) ||
+            (VT == MVT::i64 && C != INT64_MIN && isLegalCmpImmed(C - 1))) {
           CC = (CC == ISD::SETLT) ? ISD::SETLE : ISD::SETGT;
-          C = (VT == MVT::i32) ? (uint32_t)(C - 1) : C - 1;
+          C = C - 1;
+          if (VT == MVT::i32)
+            C &= 0xFFFFFFFF;
           RHS = DAG.getConstant(C, dl, VT);
         }
         break;
       case ISD::SETULT:
       case ISD::SETUGE:
-        if ((VT == MVT::i32 && C != 0 &&
-             isLegalArithImmed((uint32_t)(C - 1))) ||
-            (VT == MVT::i64 && C != 0ULL && isLegalArithImmed(C - 1ULL))) {
+        if ((VT == MVT::i32 && C != 0 && isLegalCmpImmed(C - 1)) ||
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AZero13 wrote:

> Could we keep the value as APInt, and use the APInt methods directly? Subtracking 1 from INT_MIN is UB, which I'm not sure this would protect against.

I will just bail out early. It is not like INT_MIN +/-1 in binary can be legal either

https://github.com/llvm/llvm-project/pull/140999