Conservatively handle multiple MMOs in MIsNeedChainEdge

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

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index 703ae3d9cc5..65075893e5a 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -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: