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dead code elimination: Fixed a crash when trying to get the immediate post-dominating block in an infinite loop. #16912

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Merged
merged 2 commits into from
May 30, 2018
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dead code elimination: Fixed a crash when trying to get the immediate post-dominating block in an infinite loop. #16912

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8c47ee4
tests: re-enable dead_code_elimination test.
eeckstein May 30, 2018
649c2d0
dead code elimination: Fixed a crash when trying to get the immediate…
eeckstein May 30, 2018
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13 changes: 9 additions & 4 deletions lib/SILOptimizer/Transforms/DeadCodeElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -419,10 +419,12 @@ void DCE::propagateLiveness(SILInstruction *I) {
SILBasicBlock *DCE::nearestUsefulPostDominator(SILBasicBlock *Block) {
// Find the nearest post-dominator that has useful instructions.
auto *PostDomNode = PDT->getNode(Block)->getIDom();
while (!LiveBlocks.count(PostDomNode->getBlock()))
while (PostDomNode && !LiveBlocks.count(PostDomNode->getBlock()))
PostDomNode = PostDomNode->getIDom();

return PostDomNode->getBlock();
if (PostDomNode)
return PostDomNode->getBlock();
return nullptr;
}

// Replace the given conditional branching instruction with a plain
Expand Down Expand Up @@ -485,8 +487,11 @@ bool DCE::removeDead(SILFunction &F) {
// We want to replace dead terminators with unconditional branches to
// the nearest post-dominator that has useful instructions.
if (isa<TermInst>(Inst)) {
replaceBranchWithJump(Inst,
nearestUsefulPostDominator(Inst->getParent()));
SILBasicBlock *postDom = nearestUsefulPostDominator(Inst->getParent());
if (!postDom)
continue;

replaceBranchWithJump(Inst, postDom);
Inst->eraseFromParent();
BranchesChanged = true;
Changed = true;
Expand Down
24 changes: 18 additions & 6 deletions test/SILOptimizer/dead_code_elimination.sil
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
// RUN: %target-sil-opt -assume-parsing-unqualified-ownership-sil -enable-sil-verify-all -dce %s | %FileCheck %s

// REQUIRES: rdar34013900

sil_stage canonical

import Builtin
Expand Down Expand Up @@ -59,17 +57,15 @@ bb3:
return %18 : $()
}

// We currently bail out on functions that have structurally infinite
// loops.
// CHECK-LABEL: sil @dead3
sil @dead3 : $@convention(thin) () -> () {
bb0:
// CHECK: bb0
br bb1
// CHECK: bb1
bb1:
// CHECK: integer_literal $Builtin.Int32, 0
// CHECK: br bb1
// CHECK: bb1:
// CHECK-NEXT: br bb1
%0 = integer_literal $Builtin.Int32, 0
br bb1
}
Expand Down Expand Up @@ -247,3 +243,19 @@ bb0(%0 : $*Container):
return %90 : $()
}

// Check that DCE does not crash with an infinite loop through a cond_br.
// CHECK-LABEL: sil @deal_with_infinite_loop
// CHECK: cond_br
sil @deal_with_infinite_loop : $@convention(thin) () -> () {
bb0:
br bb1

bb1:
cond_br undef, bb2, bb3

bb2:
br bb1

bb3:
br bb1
}