https://llvm.org/bugs/show_bug.cgi?id=25199
Bug ID: 25199
Summary: [BranchFolding][AArch64] AArch64LoadStoreOpt uses MMOs
which are dropped during tail merge
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: AArch64
Assignee: unassignedb...@nondot.org
Reporter: mcros...@codeaurora.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
In r231799, MMOs were removed during tail merge to preserve dependencies.
>From the commit message:
"A more robust solution would be to add multiple MMOs from the duplicate MIs to
the new MI. Currently ScheduleDAGInstrs.cpp ignores all MMOs on instructions
with multiple MMOs, so this solution is equivalent for the time being."
The final comment isn't quite true. This change doesn't effect
ScheduleDAGInstrs, but it does prevent the load/store optimization pass from
generating load/store pairs. Because the MMOs are dropped the pass
conservatively assumes the memory instructions are volatile.
>From MachineInstr::hasOrderedMemoryRef()
// Otherwise, if the instruction has no memory reference information,
// conservatively assume it wasn't preserved.
if (memoperands_empty())
return true;
This check causes the pass to bailout.
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