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[SimpleLoopUnswitch] remove a chain of dead blocks at once

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Recent change to deleteDeadBlocksFromLoop was not enough to
fix all the problems related to dead blocks after nontrivial
unswitching of switches.

We need to delete all the dead blocks that were created during
unswitching, otherwise we will keep having problems with phi's
or dead blocks.

This change removes all the dead blocks that are reachable from the loop,
not trying to track whether these blocks are newly created by unswitching
or not. While not completely correct, we are unlikely to get loose but
reachable dead blocks that do not belong to our loop nest.

It does fix all the failures currently known, in particular PR38778.

Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D51519

llvm-svn: 341398
This commit is contained in:
Fedor Sergeev 2018-09-04 20:19:41 +00:00
parent 97dfb8a76f
commit 293faf6963
2 changed files with 75 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
View File

@ -1378,25 +1378,25 @@ static void
deleteDeadBlocksFromLoop(Loop &L,
SmallVectorImpl<BasicBlock *> &ExitBlocks,
DominatorTree &DT, LoopInfo &LI) {
// Find all the dead blocks, and remove them from their successors.
SmallVector<BasicBlock *, 16> DeadBlocks;
for (BasicBlock *BB : ExitBlocks)
if (!DT.isReachableFromEntry(BB)) {
for (BasicBlock *SuccBB : successors(BB))
// Find all the dead blocks tied to this loop, and remove them from their
// successors.
SmallPtrSet<BasicBlock *, 16> DeadBlockSet;
// Start with loop/exit blocks and get a transitive closure of reachable dead
// blocks.
SmallVector<BasicBlock *, 16> DeathCandidates(ExitBlocks.begin(),
ExitBlocks.end());
DeathCandidates.append(L.blocks().begin(), L.blocks().end());
while (!DeathCandidates.empty()) {
auto *BB = DeathCandidates.pop_back_val();
if (!DeadBlockSet.count(BB) && !DT.isReachableFromEntry(BB)) {
for (BasicBlock *SuccBB : successors(BB)) {
SuccBB->removePredecessor(BB);
DeadBlocks.push_back(BB);
}
for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop())
for (BasicBlock *BB : ParentL->blocks())
if (!DT.isReachableFromEntry(BB)) {
for (BasicBlock *SuccBB : successors(BB))
SuccBB->removePredecessor(BB);
DeadBlocks.push_back(BB);
DeathCandidates.push_back(SuccBB);
}
SmallPtrSet<BasicBlock *, 16> DeadBlockSet(DeadBlocks.begin(),
DeadBlocks.end());
DeadBlockSet.insert(BB);
}
}
// Filter out the dead blocks from the exit blocks list so that it can be
// used in the caller.
@ -1405,7 +1405,7 @@ deleteDeadBlocksFromLoop(Loop &L,
// Walk from this loop up through its parents removing all of the dead blocks.
for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) {
for (auto *BB : DeadBlocks)
for (auto *BB : DeadBlockSet)
ParentL->getBlocksSet().erase(BB);
llvm::erase_if(ParentL->getBlocksVector(),
[&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
@ -1430,7 +1430,7 @@ deleteDeadBlocksFromLoop(Loop &L,
// Remove the loop mappings for the dead blocks and drop all the references
// from these blocks to others to handle cyclic references as we start
// deleting the blocks themselves.
for (auto *BB : DeadBlocks) {
for (auto *BB : DeadBlockSet) {
// Check that the dominator tree has already been updated.
assert(!DT.getNode(BB) && "Should already have cleared domtree!");
LI.changeLoopFor(BB, nullptr);

56
test/Transforms/SimpleLoopUnswitch/delete-dead-blocks.ll
View File

@ -43,3 +43,59 @@ get_out:
get_out2:
unreachable
}
;
; This comes from PR38778
; CHECK-LABEL: @Test2
define void @Test2(i32) {
header:
br label %loop
loop:
switch i32 %0, label %continue [
i32 -2147483648, label %check
i32 98, label %guarded1
i32 99, label %guarded2
]
; CHECK-NOT: {{^}}guarded1:
guarded1:
br i1 undef, label %continue, label %leave
guarded2:
br label %continue
check:
%val = add i32 0, 1
br i1 undef, label %continue, label %leave
continue:
br label %loop
leave:
%local = phi i32 [ 0, %guarded1 ], [ %val, %check ]
ret void
}
;
; Yet another test from PR38778
;
; CHECK-LABEL: @Test3
define void @Test3(i32) {
header:
br label %outer
outer:
%bad_input.i = icmp eq i32 %0, -2147483648
br label %inner
inner:
br i1 %bad_input.i, label %overflow, label %switchme
overflow:
br label %continue
switchme:
switch i32 %0, label %continue [
i32 88, label %go_out
i32 99, label %case2
]
; CHECK-NOT: {{^}}case2:
case2:
br label %continue
continue:
%local_11_92 = phi i32 [ 0, %switchme ], [ 18, %case2 ], [ 0, %overflow ]
br i1 undef, label %outer, label %inner
go_out:
unreachable
}