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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).

llvm-svn: 198795
This commit is contained in:
Hal Finkel 2014-01-08 21:52:02 +00:00
parent a64ee177a0
commit 2150e3a743
2 changed files with 41 additions and 4 deletions
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8
llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
View File

@ -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:

37
llvm/test/CodeGen/X86/misched-aa-mmos.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: llc -enable-misched -enable-aa-sched-mi < %s
; This generates a decw instruction, which has two MMOs, and an alias SU edge
; query involving that instruction. Make sure this does not crash.
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
%s1 = type { i16, i16, i32 }
%c1 = type { %s1*, %u1, i16, i8 }
%u1 = type { i64 }
declare zeroext i1 @bar(i64*, i32) #5
define i32 @foo() #0 align 2 {
entry:
%temp_rhs = alloca %c1, align 8
br i1 undef, label %if.else56, label %cond.end.i
cond.end.i:
%significand.i18.i = getelementptr inbounds %c1* %temp_rhs, i64 0, i32 1
%exponent.i = getelementptr inbounds %c1* %temp_rhs, i64 0, i32 2
%0 = load i16* %exponent.i, align 8
%sub.i = add i16 %0, -1
store i16 %sub.i, i16* %exponent.i, align 8
%parts.i.i = bitcast %u1* %significand.i18.i to i64**
%1 = load i64** %parts.i.i, align 8
%call5.i = call zeroext i1 @bar(i64* %1, i32 undef) #1
unreachable
if.else56:
unreachable
}
attributes #0 = { nounwind uwtable }
attributes #1 = { nounwind }