NewRHS =
ICmp->getOperand(S == InvariantRHS ? IVOperIdx : (1 - IVOperIdx));
- for (Value *Incoming : cast<PHINode>(IVOperand)->incoming_values()) {
- if (NewLHS && NewRHS)
- break;
+ auto *PN = cast<PHINode>(IVOperand);
+ for (unsigned i = 0, e = PN->getNumIncomingValues();
+ i != e && (!NewLHS || !NewRHS);
+ ++i) {
+
+ // If this is a value incoming from the backedge, then it cannot be a loop
+ // invariant value (since we know that IVOperand is an induction variable).
+ if (L->contains(PN->getIncomingBlock(i)))
+ continue;
+
+ // NB! This following assert does not fundamentally have to be true, but
+ // it is true today given how SCEV analyzes induction variables.
+ // Specifically, today SCEV will *not* recognize %iv as an induction
+ // variable in the following case:
+ //
+ // define void @f(i32 %k) {
+ // entry:
+ // br i1 undef, label %r, label %l
+ //
+ // l:
+ // %k.inc.l = add i32 %k, 1
+ // br label %loop
+ //
+ // r:
+ // %k.inc.r = add i32 %k, 1
+ // br label %loop
+ //
+ // loop:
+ // %iv = phi i32 [ %k.inc.l, %l ], [ %k.inc.r, %r ], [ %iv.inc, %loop ]
+ // %iv.inc = add i32 %iv, 1
+ // br label %loop
+ // }
+ //
+ // but if it starts to, at some point, then the assertion below will have
+ // to be changed to a runtime check.
+
+ Value *Incoming = PN->getIncomingValue(i);
+
+#ifndef NDEBUG
+ if (auto *I = dyn_cast<Instruction>(Incoming))
+ assert(DT->dominates(I, ICmp) && "Should be a unique loop dominating value!");
+#endif
const SCEV *IncomingS = SE->getSCEV(Incoming);