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Revert "[IfConversion] Keep the CFG updated incrementally in IfConvertTriangle"

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The reverted change introdued assertions ala:

"MachineBasicBlock::succ_iterator
llvm::MachineBasicBlock::removeSuccessor(succ_iterator, bool): Assertion
`I != Successors.end() && "Not a current successor!"'

Mikael, the original committer, wrote me that he is working on a fix, but that
it likely will take some time to get this resolved. As this bug is one of the
last two issues that keep the AOSP buildbot from turning green, I revert the
original commit r302876.

I am looking forward to see this recommitted after the assertion has been
resolved.

llvm-svn: 304128
This commit is contained in:
Tobias Grosser 2017-05-29 06:12:18 +00:00
parent 86f4730576
commit 5d54610f39
2 changed files with 6 additions and 45 deletions
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27
lib/CodeGen/IfConversion.cpp
View File

@ -1588,32 +1588,22 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
BBCvt = MBPI->getEdgeProbability(BBI.BB, &CvtMBB);
}
// To be able to insert code freely at the end of BBI we sometimes remove
// the branch from BBI to NextMBB temporarily. Remember if this happened.
bool RemovedBranchToNextMBB = false;
if (CvtMBB.pred_size() > 1) {
BBI.NonPredSize -= TII->removeBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
// the entry block.
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
// Keep the CFG updated.
// RemoveExtraEdges won't work if the block has an unanalyzable branch, so
// explicitly remove CvtBBI as a successor.
BBI.BB->removeSuccessor(&CvtMBB, true);
} else {
// Predicate the 'true' block after removing its branch.
CvtBBI->NonPredSize -= TII->removeBranch(CvtMBB);
PredicateBlock(*CvtBBI, CvtMBB.end(), Cond);
// Remove the branch from the entry of the triangle to NextBB to be able to
// do the merge below. Keep the CFG updated, but remember we removed the
// branch since we do want to execute NextMBB, either by introducing a
// branch to it again, or merging it into the entry block.
// How it's handled is decided further down.
BBI.NonPredSize -= TII->removeBranch(*BBI.BB);
BBI.BB->removeSuccessor(&NextMBB, true);
RemovedBranchToNextMBB = true;
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->removeBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI, false);
}
@ -1651,19 +1641,12 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
if (!HasEarlyExit &&
// We might have removed BBI from NextMBB's predecessor list above but
// we want it to be there, so consider that too.
(NextMBB.pred_size() == (RemovedBranchToNextMBB ? 0 : 1)) &&
!NextBBI->HasFallThrough &&
NextMBB.pred_size() == 1 && !NextBBI->HasFallThrough &&
!NextMBB.hasAddressTaken()) {
// We will merge NextBBI into BBI, and thus remove the current
// fallthrough from BBI into CvtBBI.
BBI.BB->removeSuccessor(&CvtMBB, true);
MergeBlocks(BBI, *NextBBI);
FalseBBDead = true;
} else {
InsertUncondBranch(*BBI.BB, NextMBB, TII);
BBI.BB->addSuccessor(&NextMBB);
BBI.HasFallThrough = false;
}
// Mixed predicated and unpredicated code. This cannot be iteratively
@ -1671,6 +1654,8 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (!IterIfcvt)
BBI.IsDone = true;

24
test/CodeGen/MIR/ARM/PR32721_ifcvt_triangle_unanalyzable.mir
View File

@ -1,24 +0,0 @@
# RUN: llc -mtriple=arm-apple-ios -run-pass=if-converter %s -o - | FileCheck %s
---
name: foo
body: |
bb.0:
B %bb.2
bb.1:
BX_RET 14, 0
bb.2:
Bcc %bb.1, 1, %cpsr
bb.3:
B %bb.1
...
# We should get a single block containing the BX_RET, with no successors at all
# CHECK: body:
# CHECK-NEXT: bb.0:
# CHECK-NEXT: BX_RET