[llvm] [AArch64] Adjust comparison constant if adjusting it means less instructions (PR #151024)

[David Green via llvm-commits]

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@@ -3969,42 +3977,45 @@ static SDValue getAArch64Cmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
       case ISD::SETGE:
         if (!C.isMinSignedValue()) {
           APInt CMinusOne = C - 1;
-          if (isLegalCmpImmed(CMinusOne)) {
+          if (isLegalCmpImmed(CMinusOne) ||
+              (NumImmForC > numberOfInstrToLoadImm(CMinusOne))) {
             CC = (CC == ISD::SETLT) ? ISD::SETLE : ISD::SETGT;
             RHS = DAG.getConstant(CMinusOne, DL, VT);
           }
         }
         break;
       case ISD::SETULT:
-      case ISD::SETUGE:
-        if (!C.isZero()) {
-          APInt CMinusOne = C - 1;
-          if (isLegalCmpImmed(CMinusOne)) {
-            CC = (CC == ISD::SETULT) ? ISD::SETULE : ISD::SETUGT;
-            RHS = DAG.getConstant(CMinusOne, DL, VT);
-          }
+      case ISD::SETUGE: {
+        // C is not 0 because it is a legal immediate.
+        APInt CMinusOne = C - 1;
+        if (isLegalCmpImmed(CMinusOne) ||
+            (NumImmForC > numberOfInstrToLoadImm(CMinusOne))) {
+          CC = (CC == ISD::SETULT) ? ISD::SETULE : ISD::SETUGT;
+          RHS = DAG.getConstant(CMinusOne, DL, VT);
         }
-        break;
+      } break;
       case ISD::SETLE:
       case ISD::SETGT:
         if (!C.isMaxSignedValue()) {
           APInt CPlusOne = C + 1;
-          if (isLegalCmpImmed(CPlusOne)) {
+          if (isLegalCmpImmed(CPlusOne) ||
+              (NumImmForC > numberOfInstrToLoadImm(CPlusOne))) {
             CC = (CC == ISD::SETLE) ? ISD::SETLT : ISD::SETGE;
             RHS = DAG.getConstant(CPlusOne, DL, VT);
           }
         }
         break;
       case ISD::SETULE:
-      case ISD::SETUGT:
-        if (!C.isAllOnes()) {
-          APInt CPlusOne = C + 1;
-          if (isLegalCmpImmed(CPlusOne)) {
-            CC = (CC == ISD::SETULE) ? ISD::SETULT : ISD::SETUGE;
-            RHS = DAG.getConstant(CPlusOne, DL, VT);
-          }
+      case ISD::SETUGT: {
+        // The maxmimum possible number, -1, is a legal cmp immediate, so no
+        // need to check for it.
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davemgreen wrote:

Same here for the assert and the }.

https://github.com/llvm/llvm-project/pull/151024