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[LoopInfo] Factor use-scan of isBlockInLCSSAForm [NFC] (#211087)

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[Factored out of llvm/llvm-project#151062 by review request; AI
Disclosure: Done by Claude]

Split the per-use logic of isBlockInLCSSAForm into a separate helper
that answers whether a single use of a value defined in a loop is
contained within the loop for LCSSA purposes.
This commit is contained in:
Keno Fischer 2026-07-22 01:08:03 -04:00 committed by GitHub
parent 6793bb48ac
commit a67429f21b
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1 changed files with 25 additions and 15 deletions
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40
llvm/lib/Analysis/LoopInfo.cpp
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@ -449,6 +449,30 @@ bool Loop::isCanonical(ScalarEvolution &SE) const {
return true;
}
// Check whether the use \p U of a value defined in block \p BB (which is part
// of loop \p L) does not require a live-out phi, i.e. whether it is contained
// in the loop for LCSSA purposes.
static bool loopContainsUser(const Loop &L, const BasicBlock &BB, const Use &U,
const DominatorTree &DT) {
const Instruction *UI = cast<Instruction>(U.getUser());
const BasicBlock *UserBB = UI->getParent();
// For practical purposes, we consider that the use in a PHI
// occurs in the respective predecessor block. For more info,
// see the `phi` doc in LangRef and the LCSSA doc.
if (const PHINode *P = dyn_cast<PHINode>(UI))
UserBB = P->getIncomingBlock(U);
// Check the current block, as a fast-path, before checking whether
// the use is anywhere in the loop. Most values are used in the same
// block they are defined in. Also, blocks not reachable from the
// entry are special; uses in them don't need to go through PHIs.
if (UserBB != &BB && !L.contains(UserBB) && DT.isReachableFromEntry(UserBB))
return false;
return true;
}
// Check that 'BB' doesn't have any uses outside of the 'L'
static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
const DominatorTree &DT, bool IgnoreTokens) {
@ -460,21 +484,7 @@ static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
continue;
for (const Use &U : I.uses()) {
const Instruction *UI = cast<Instruction>(U.getUser());
const BasicBlock *UserBB = UI->getParent();
// For practical purposes, we consider that the use in a PHI
// occurs in the respective predecessor block. For more info,
// see the `phi` doc in LangRef and the LCSSA doc.
if (const PHINode *P = dyn_cast<PHINode>(UI))
UserBB = P->getIncomingBlock(U);
// Check the current block, as a fast-path, before checking whether
// the use is anywhere in the loop. Most values are used in the same
// block they are defined in. Also, blocks not reachable from the
// entry are special; uses in them don't need to go through PHIs.
if (UserBB != &BB && !L.contains(UserBB) &&
DT.isReachableFromEntry(UserBB))
if (!loopContainsUser(L, BB, U, DT))
return false;
}
}