[PATCH] D107803: [SimpifyCFG] Remove recursion from FoldCondBranchOnPHI. NFCI.
Carl Ritson via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 10 01:16:05 PDT 2021
critson created this revision.
critson added reviewers: lebedev.ri, fhahn, nikic, spatel.
Herald added a subscriber: hiraditya.
critson requested review of this revision.
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Herald added a subscriber: llvm-commits.
Avoid stack overflow errors on systems with small stack sizes
by removing recursion in FoldCondBranchOnPHI.
This is a simple change as the recursion was only iteratively
calling the function again on the same arguments.
Ideally this would be compiled to a tail call, but there is
no guarantee.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D107803
Files:
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2606,8 +2606,10 @@
/// If we have a conditional branch on a PHI node value that is defined in the
/// same block as the branch and if any PHI entries are constants, thread edges
/// corresponding to that entry to be branches to their ultimate destination.
-static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
- const DataLayout &DL, AssumptionCache *AC) {
+static Optional<bool> FoldCondBranchOnPHIImpl(BranchInst *BI,
+ DomTreeUpdater *DTU,
+ const DataLayout &DL,
+ AssumptionCache *AC) {
BasicBlock *BB = BI->getParent();
PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
// NOTE: we currently cannot transform this case if the PHI node is used
@@ -2721,13 +2723,24 @@
DTU->applyUpdates(Updates);
}
- // Recurse, simplifying any other constants.
- return FoldCondBranchOnPHI(BI, DTU, DL, AC) || true;
+ // Signal repeat, simplifying any other constants.
+ return Optional<bool>();
}
return false;
}
+static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
+ const DataLayout &DL, AssumptionCache *AC) {
+ Optional<bool> Result;
+ unsigned Iterations = 0;
+ do {
+ Result = FoldCondBranchOnPHIImpl(BI, DTU, DL, AC);
+ Iterations++;
+ } while (!Result);
+ return *Result || Iterations > 1;
+}
+
/// Given a BB that starts with the specified two-entry PHI node,
/// see if we can eliminate it.
static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
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