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[JumpThreading] Stop searching predecessor when the current bb is in a 

unreachable loop.

updatePredecessorProfileMetadata in jumpthreading tries to find the
first dominating predecessor block for a PHI value by searching upwards
the predecessor block chain.

But jumpthreading may see some temporary IR state which contains
unreachable bb not being cleaned up. If an unreachable loop happens to
be on the predecessor block chain, keeping chasing the predecessor
block will run into an infinite loop.

The patch fixes it.

Differential Revision: https://reviews.llvm.org/D65310

llvm-svn: 367154
This commit is contained in:
Wei Mi 2019-07-26 20:59:22 +00:00
parent fe4b12b4de
commit 55a68a2400
2 changed files with 74 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
llvm/lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -224,13 +224,21 @@ static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) {
BasicBlock *PhiBB) -> std::pair<BasicBlock *, BasicBlock *> {
auto *PredBB = IncomingBB;
auto *SuccBB = PhiBB;
SmallPtrSet<BasicBlock *, 16> Visited;
while (true) {
BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
if (PredBr && PredBr->isConditional())
return {PredBB, SuccBB};
Visited.insert(PredBB);
auto *SinglePredBB = PredBB->getSinglePredecessor();
if (!SinglePredBB)
return {nullptr, nullptr};
// Stop searching when SinglePredBB has been visited. It means we see
// an unreachable loop.
if (Visited.count(SinglePredBB))
return {nullptr, nullptr};
SuccBB = PredBB;
PredBB = SinglePredBB;
}
@ -253,7 +261,9 @@ static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) {
return;
BasicBlock *PredBB = PredOutEdge.first;
BranchInst *PredBr = cast<BranchInst>(PredBB->getTerminator());
BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
if (!PredBr)
return;
uint64_t PredTrueWeight, PredFalseWeight;
// FIXME: We currently only set the profile data when it is missing.

63
llvm/test/Transforms/JumpThreading/unreachable-loops.ll Normal file
View File

@ -0,0 +1,63 @@
; RUN: opt -jump-threading -S < %s | FileCheck %s
; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
; Check the unreachable loop won't cause infinite loop
; in jump-threading when it tries to update the predecessors'
; profile metadata from a phi node.
define void @unreachable_single_bb_loop() {
; CHECK-LABEL: @unreachable_single_bb_loop()
bb:
%tmp = call i32 @a()
%tmp1 = icmp eq i32 %tmp, 1
br i1 %tmp1, label %bb5, label %bb8
; unreachable single bb loop.
bb2: ; preds = %bb2
%tmp4 = icmp ne i32 %tmp, 1
switch i1 %tmp4, label %bb2 [
i1 0, label %bb5
i1 1, label %bb8
]
bb5: ; preds = %bb2, %bb
%tmp6 = phi i1 [ %tmp1, %bb ], [ false, %bb2 ]
br i1 %tmp6, label %bb8, label %bb7, !prof !0
bb7: ; preds = %bb5
br label %bb8
bb8: ; preds = %bb8, %bb7, %bb5, %bb2
ret void
}
define void @unreachable_multi_bbs_loop() {
; CHECK-LABEL: @unreachable_multi_bbs_loop()
bb:
%tmp = call i32 @a()
%tmp1 = icmp eq i32 %tmp, 1
br i1 %tmp1, label %bb5, label %bb8
; unreachable two bbs loop.
bb3: ; preds = %bb2
br label %bb2
bb2: ; preds = %bb3
%tmp4 = icmp ne i32 %tmp, 1
switch i1 %tmp4, label %bb3 [
i1 0, label %bb5
i1 1, label %bb8
]
bb5: ; preds = %bb2, %bb
%tmp6 = phi i1 [ %tmp1, %bb ], [ false, %bb2 ]
br i1 %tmp6, label %bb8, label %bb7, !prof !0
bb7: ; preds = %bb5
br label %bb8
bb8: ; preds = %bb8, %bb7, %bb5, %bb2
ret void
}
declare i32 @a()
!0 = !{!"branch_weights", i32 2146410443, i32 1073205}