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Conservatively handle multiple MMOs in MIsNeedChainEdge

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MIsNeedChainEdge, which is used by -enable-aa-sched-mi (AA in misched), had an
llvm_unreachable when -enable-aa-sched-mi is enabled and we reach an
instruction with multiple MMOs. Instead, return a conservative answer. This
allows testing -enable-aa-sched-mi on x86.

Also, this moves the check above the isUnsafeMemoryObject checks.
isUnsafeMemoryObject is currently correct only for instructions with one MMO
(as noted in the comment in isUnsafeMemoryObject):

  // We purposefully do no check for hasOneMemOperand() here
  // in hope to trigger an assert downstream in order to
  // finish implementation.

The problem with this is that, had the candidate edge passed the
"!MIa->mayStore() && !MIb->mayStore()" check, the hoped-for assert would never
happen (which could, in theory, lead to incorrect behavior if one of these
secondary MMOs was volatile, for example).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198795 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-01-08 21:52:02 +00:00
parent b9271b0ec5
commit 5bbbb37ff2
2 changed files with 41 additions and 4 deletions
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8
lib/CodeGen/ScheduleDAGInstrs.cpp
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@@ -512,6 +512,10 @@ static bool MIsNeedChainEdge(AliasAnalysis *AA, const MachineFrameInfo *MFI,
if (MIa == MIb)
return false;
// FIXME: Need to handle multiple memory operands to support all targets.
if (!MIa->hasOneMemOperand() || !MIb->hasOneMemOperand())
return true;
if (isUnsafeMemoryObject(MIa, MFI) || isUnsafeMemoryObject(MIb, MFI))
return true;
@@ -527,10 +531,6 @@ static bool MIsNeedChainEdge(AliasAnalysis *AA, const MachineFrameInfo *MFI,
MachineMemOperand *MMOa = *MIa->memoperands_begin();
MachineMemOperand *MMOb = *MIb->memoperands_begin();
// FIXME: Need to handle multiple memory operands to support all targets.
if (!MIa->hasOneMemOperand() || !MIb->hasOneMemOperand())
llvm_unreachable("Multiple memory operands.");
// The following interface to AA is fashioned after DAGCombiner::isAlias
// and operates with MachineMemOperand offset with some important
// assumptions: