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SimplifyCFG: fix an infinite jump-threading loop. #35614

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Merged
merged 1 commit into from
Jan 27, 2021
Merged

SimplifyCFG: fix an infinite jump-threading loop. #35614

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8 changes: 8 additions & 0 deletions lib/SILOptimizer/Transforms/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -302,6 +302,8 @@ bool SimplifyCFG::threadEdge(const ThreadInfo &ti) {
return false;

Cloner.cloneBranchTarget(SrcTerm);
JumpThreadingCost[Cloner.getNewBB()] = JumpThreadingCost[SrcTerm->getDestBB()];


// We have copied the threaded block into the edge.
auto *clonedSrc = Cloner.getNewBB();
Expand Down Expand Up @@ -1112,6 +1114,10 @@ bool SimplifyCFG::tryJumpThreading(BranchInst *BI) {
Cloner.cloneBranchTarget(BI);
Cloner.updateSSAAfterCloning();

// Also account the costs to the cloned DestBB, so the jump threading cannot
// loop by cloning the cloned block again.
JumpThreadingCost[Cloner.getNewBB()] += copyCosts;

// Once all the instructions are copied, we can nuke BI itself. We also add
// the threaded and edge block to the worklist now that they (likely) can be
// simplified.
Expand Down Expand Up @@ -2852,6 +2858,8 @@ bool SimplifyCFG::tailDuplicateObjCMethodCallSuccessorBlocks() {
Cloner.cloneBranchTarget(Branch);
Cloner.updateSSAAfterCloning();

JumpThreadingCost[Cloner.getNewBB()] = JumpThreadingCost[DestBB];

Changed = true;
// Simplify the cloned block and continue tail duplicating through its new
// successors edges.
Expand Down