[llvm] change contents of ScalarEvolution from private to protected (PR #83052)

[Eli Friedman via llvm-commits]

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@@ -9204,16 +9270,33 @@ ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromICmp(
   }
   case ICmpInst::ICMP_SGE:
   case ICmpInst::ICMP_UGE:
-    // Since the loop is finite, an invariant RHS cannot include the boundary
-    // value, otherwise it would loop forever.
-    if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
-        !isLoopInvariant(RHS, L))
-      break;
-    RHS = getAddExpr(getMinusOne(RHS->getType()), RHS);
+    if (!AssumeLoopFinite) {
+      // Since the loop is finite, an invariant RHS cannot include the boundary
+      // value, otherwise it would loop forever.
+      if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
+          !isLoopInvariant(RHS, L))
+        break;
+      RHS = getAddExpr(getMinusOne(RHS->getType()), RHS);
+    }
     [[fallthrough]];
   case ICmpInst::ICMP_SGT:
   case ICmpInst::ICMP_UGT: { // while (X > Y)
     bool IsSigned = ICmpInst::isSigned(Pred);
+    if (AssumeLoopFinite) {
+      if (Pred == ICmpInst::ICMP_SGE || Pred == ICmpInst::ICMP_UGE) {
+        if (!isa<IntegerType>(RHS->getType()))
+          break;
+        SmallVector<const SCEV *, 2> sv = {
+            RHS, getConstant(
+                     ConstantInt::get(cast<IntegerType>(RHS->getType()), -1))};
+        // Since this is not an infinite loop by induction, RHS cannot be
+        // int_min/uint_min Therefore subtracting 1 does not wrap.
+        if (IsSigned)
+          RHS = getAddExpr(sv, SCEV::FlagNSW);
+        else
+          RHS = getAddExpr(sv, SCEV::FlagNUW);
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efriedma-quic wrote:

This looks like duplicated code from above (the EnableFiniteLoopControl bit).

https://github.com/llvm/llvm-project/pull/83052