[MachineCombiner] Fix initialisation of LastUpdate for incremental update.
Summary:
Fixes a bogus iterator resulting from the removal of a block's first instruction at the point that incremental update is enabled.
Patch by Paul Walker.
Reviewers: fhahn, Gerolf, efriedma, MatzeB
Reviewed By: fhahn
Subscribers: aemerson, javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D38734
llvm-svn: 315502
diff --git a/llvm/lib/CodeGen/MachineCombiner.cpp b/llvm/lib/CodeGen/MachineCombiner.cpp
index d563370..3ffef68 100644
--- a/llvm/lib/CodeGen/MachineCombiner.cpp
+++ b/llvm/lib/CodeGen/MachineCombiner.cpp
@@ -415,7 +415,7 @@
bool IncrementalUpdate = false;
auto BlockIter = MBB->begin();
- auto LastUpdate = BlockIter;
+ decltype(BlockIter) LastUpdate;
// Check if the block is in a loop.
const MachineLoop *ML = MLI->getLoopFor(MBB);
if (!MinInstr)
@@ -503,9 +503,11 @@
InstrIdxForVirtReg, P,
!IncrementalUpdate) &&
preservesResourceLen(MBB, BlockTrace, InsInstrs, DelInstrs)) {
- if (MBB->size() > inc_threshold)
+ if (MBB->size() > inc_threshold) {
// Use incremental depth updates for basic blocks above treshold
IncrementalUpdate = true;
+ LastUpdate = BlockIter;
+ }
insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, MinInstr,
RegUnits, IncrementalUpdate);