[ARM] Check correct instructions for load/store rescheduling.

    
This code starts from the high end of the sorted vector of offsets, and
works backwards: it tries to find contiguous offsets, process them, then
pops them from the end of the vector. Most of the code agrees with this
order of processing, but one loop doesn't: it instead processes elements
from the low end of the vector (which are nodes with unrelated offsets).
Fix that loop to process the correct elements.
    
This has a few implications. One, we don't incorrectly return early when
processing multiple groups of offsets in the same block (which allows
rescheduling prera-ldst-insertpt.mir). Two, we pick the correct insert
point for loads, so they're correctly sorted (which affects the
scheduling of vldm-liveness.ll). I think it might also impact some of
the heuristics slightly.
    
Differential Revision: https://reviews.llvm.org/D30368

llvm-svn: 296701

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
index 8e51f13..f9eec7d 100644
--- a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -2195,7 +2195,7 @@ bool ARMPreAllocLoadStoreOpt::RescheduleOps(MachineBasicBlock *MBB,
     else {
       SmallPtrSet<MachineInstr*, 4> MemOps;
       SmallSet<unsigned, 4> MemRegs;
-      for (int i = NumMove-1; i >= 0; --i) {
+      for (size_t i = Ops.size() - NumMove, e = Ops.size(); i != e; ++i) {
         MemOps.insert(Ops[i]);
         MemRegs.insert(Ops[i]->getOperand(0).getReg());
       }