[llvm] a1783b5 - [SimpifyCFG] Remove recursion from FoldCondBranchOnPHI. NFCI.
Carl Ritson via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 10 03:33:54 PDT 2021
Author: Carl Ritson
Date: 2021-08-10T19:14:31+09:00
New Revision: a1783b54e8b873c4a668259ae69bfc150f879dca
URL: https://github.com/llvm/llvm-project/commit/a1783b54e8b873c4a668259ae69bfc150f879dca
DIFF: https://github.com/llvm/llvm-project/commit/a1783b54e8b873c4a668259ae69bfc150f879dca.diff
LOG: [SimpifyCFG] Remove recursion from FoldCondBranchOnPHI. NFCI.
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.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D107803
Added:
Modified:
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index a72af2bbe0b88..e581dfd2c3ce1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2606,8 +2606,10 @@ static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
/// 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 +2723,25 @@ static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
DTU->applyUpdates(Updates);
}
- // Recurse, simplifying any other constants.
- return FoldCondBranchOnPHI(BI, DTU, DL, AC) || true;
+ // Signal repeat, simplifying any other constants.
+ return None;
}
return false;
}
+static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
+ const DataLayout &DL, AssumptionCache *AC) {
+ Optional<bool> Result;
+ bool EverChanged = false;
+ do {
+ // Note that None means "we changed things, but recurse further."
+ Result = FoldCondBranchOnPHIImpl(BI, DTU, DL, AC);
+ EverChanged |= Result == None || *Result;
+ } while (Result == None);
+ return EverChanged;
+}
+
/// 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,
More information about the llvm-commits
mailing list