[llvm] [SimplifyIndVar] ICMP predicate conversion to EQ/NE (PR #144945)

[Philip Reames via llvm-commits]

================
@@ -244,6 +245,128 @@ bool SimplifyIndvar::makeIVComparisonInvariant(ICmpInst *ICmp,
   return true;
 }
 
+/// Try to change predicate of ICmp to EQ/NE to facilitate better work of OSR.
+/// This can be done only if all possible IV values but one lead to the same
+/// produced comparison result, while the 'chosen one' value gives the opposite
+/// result.
+bool SimplifyIndvar::forceEqualityForICmp(ICmpInst *ICmp,
+                                          Instruction *IVOperand) {
+  if (ICmp->isEquality()) {
+    // nothing to do
+    return false;
+  }
+
+  unsigned BoundOperandIdx = IVOperand == ICmp->getOperand(0) ? 1 : 0;
+  const SCEV *BoundSCEV = SE->getSCEV(ICmp->getOperand(BoundOperandIdx));
+  const SCEVConstant *BoundC = dyn_cast<SCEVConstant>(BoundSCEV);
+  CmpInst::Predicate OrigPredicate = ICmp->getPredicate();
+  CmpInst::Predicate NewPredicate = CmpInst::BAD_ICMP_PREDICATE;
+  Type *Ty = IVOperand->getType();
+  APInt NewBoundA;
+
+  if (BoundC) {
+    // Try to find the 'chosen one' value basing on predicate type and bound
+    const APInt &BoundA = BoundC->getAPInt();
+    ConstantRange ExactCR =
+        ConstantRange::makeExactICmpRegion(OrigPredicate, BoundA);
+    if (!ExactCR.getEquivalentICmp(NewPredicate, NewBoundA)) {
+      NewPredicate = CmpInst::BAD_ICMP_PREDICATE;
+    }
+  }
+
+  if (!ICmpInst::isEquality(NewPredicate)) {
+    const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IVOperand));
+    if (!AR) {
----------------
preames wrote:

AddRec could be in a different loop than ICmp.  Either a parent, or a sibling.

https://github.com/llvm/llvm-project/pull/144945