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[Analysis] Print out unreachable loops

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Summary:
When writing a loop pass I made a mistake and hit the assertion
"Unreachable block in loop". Later, I hit an assertion when I called
`BasicBlock::eraseFromParent()` incorrectly: "Use still stuck around
after Def is destroyed". This latter assertion, however, printed out
exactly which value is being deleted and what uses remain, which helped
me debug the issue.

To help people debugging their loop passes in the future, print out
exactly which basic block is unreachable in a loop.

Reviewers: sanjoy, hfinkel, mehdi_amini

Reviewed By: mehdi_amini

Subscribers: mzolotukhin

Differential Revision: https://reviews.llvm.org/D32878

llvm-svn: 302354
This commit is contained in:
Brian Gesiak 2017-05-06 16:22:53 +00:00
parent 12866b2f4e
commit cac3cd7be1
1 changed files with 12 additions and 4 deletions
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16
include/llvm/Analysis/LoopInfoImpl.h
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@ -220,8 +220,8 @@ void LoopBase<BlockT, LoopT>::verifyLoop() const {
BI = df_ext_begin(getHeader(), VisitSet),
BE = df_ext_end(getHeader(), VisitSet);
// Keep track of the number of BBs visited.
unsigned NumVisited = 0;
// Keep track of the BBs visited.
SmallPtrSet<BlockT*, 8> VisitedBBs;
// Check the individual blocks.
for ( ; BI != BE; ++BI) {
@ -259,10 +259,18 @@ void LoopBase<BlockT, LoopT>::verifyLoop() const {
assert(BB != &getHeader()->getParent()->front() &&
"Loop contains function entry block!");
NumVisited++;
VisitedBBs.insert(BB);
}
assert(NumVisited == getNumBlocks() && "Unreachable block in loop");
if (VisitedBBs.size() != getNumBlocks()) {
dbgs() << "The following blocks are unreachable in the loop: ";
for (auto BB : Blocks) {
if (!VisitedBBs.count(BB)) {
dbgs() << *BB << "\n";
}
}
assert(false && "Unreachable block in loop");
}
// Check the subloops.
for (iterator I = begin(), E = end(); I != E; ++I)