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Merged
merged 3 commits into from
Feb 27, 2025
Merged

[JumpThreading] Remove deleted BB from Unreachable #126984

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73ce961
[JumpThreading] Remove deleted BB from Unreachable
weiguozhi Feb 12, 2025
30a97d4
[JumpThreading] Bail out maybeMergeBasicBlockIntoOnlyPred if SinglePr…
weiguozhi Feb 14, 2025
6df69dc
Regenerate the test result so the whole IR is included.
weiguozhi Feb 26, 2025
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4 changes: 4 additions & 0 deletions llvm/include/llvm/Transforms/Scalar/JumpThreading.h
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Original file line number Diff line number Diff line change
Expand Up @@ -94,6 +94,10 @@ class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> {
SmallPtrSet<const BasicBlock *, 16> LoopHeaders;
#endif

// JumpThreading must not processes blocks unreachable from entry. It's a
// waste of compute time and can potentially lead to hangs.
SmallPtrSet<BasicBlock *, 16> Unreachable;

unsigned BBDupThreshold;
unsigned DefaultBBDupThreshold;

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10 changes: 7 additions & 3 deletions llvm/lib/Transforms/Scalar/JumpThreading.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -307,12 +307,11 @@ bool JumpThreadingPass::runImpl(Function &F_, FunctionAnalysisManager *FAM_,
else
BBDupThreshold = DefaultBBDupThreshold;

// JumpThreading must not processes blocks unreachable from entry. It's a
// waste of compute time and can potentially lead to hangs.
SmallPtrSet<BasicBlock *, 16> Unreachable;
assert(DTU && "DTU isn't passed into JumpThreading before using it.");
assert(DTU->hasDomTree() && "JumpThreading relies on DomTree to proceed.");
DominatorTree &DT = DTU->getDomTree();

Unreachable.clear();
for (auto &BB : *F)
if (!DT.isReachableFromEntry(&BB))
Unreachable.insert(&BB);
Expand Down Expand Up @@ -1895,6 +1894,11 @@ bool JumpThreadingPass::maybeMergeBasicBlockIntoOnlyPred(BasicBlock *BB) {
SinglePred == BB || hasAddressTakenAndUsed(BB))
return false;

// MergeBasicBlockIntoOnlyPred may delete SinglePred, we need to avoid
// deleting a BB pointer from Unreachable.
if (Unreachable.count(SinglePred))
return false;

// If SinglePred was a loop header, BB becomes one.
if (LoopHeaders.erase(SinglePred))
LoopHeaders.insert(BB);
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13 changes: 12 additions & 1 deletion llvm/test/Transforms/JumpThreading/pr62908.ll
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Can you please regenerate the test so the whole IR is visible?

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done.

Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,18 @@

define i32 @test() {
; CHECK-LABEL: define i32 @test() {
; CHECK-NEXT: end:
; CHECK-NEXT: join.thread:
; CHECK-NEXT: br label [[END:%.*]]
; CHECK: unreachable:
; CHECK-NEXT: [[SH_PROM:%.*]] = zext i32 -1 to i64
; CHECK-NEXT: [[SHL:%.*]] = shl nsw i64 -1, [[SH_PROM]]
; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[SHL]] to i32
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: join:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[CONV]], [[UNREACHABLE:%.*]] ]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[PHI]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[END]], label [[END]]
; CHECK: end:
; CHECK-NEXT: ret i32 0
;
entry:
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