[llvm] [LV] Ignore some costs when loop gets fully unrolled (PR #106699)

[Kazu Hirata via llvm-commits]

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@@ -2682,6 +2682,25 @@ static Value *getExpandedStep(const InductionDescriptor &ID,
   return I->second;
 }
 
+/// Knowing that loop \p L executes a single vector iteration, add instructions
+/// that will get simplified and thus should not have any cost to \p
+/// InstsToIgnore.
+static void addFullyUnrolledInstructionsToIgnore(
+    Loop *L, const LoopVectorizationLegality::InductionList &IL,
+    SmallPtrSetImpl<Instruction *> &InstsToIgnore) {
+  auto *Cmp = L->getLatchCmpInst();
+  if (Cmp)
+    InstsToIgnore.insert(Cmp);
+  for (const auto &[IV, IndDesc] : IL) {
+    // Get next iteration value of the induction variable.
+    Instruction *IVInst =
+        cast<Instruction>(IV->getIncomingValueForBlock(L->getLoopLatch()));
+    if (all_of(IVInst->users(),
+               [&](const User *U) { return U == IV || U == Cmp; }))
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kazutakahirata wrote:

I've fixed a warning from this PR with: https://github.com/llvm/llvm-project/commit/9099d694f6f7e84853d6add9c58a6535cdc62b3d

https://github.com/llvm/llvm-project/pull/106699