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sched: fix latency of memory dependence chain edges for consistency.
For store->load dependencies that may alias, we should always use TrueMemOrderLatency, which may eventually become a subtarget hook. In effect, we should guarantee at least TrueMemOrderLatency on at least one DAG path from a store to a may-alias load. This should fix the standard mode as well as -enable-aa-sched-mi". git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158380 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick
parent
9df55eed04
commit
1c2d3c538c
@ -639,7 +639,8 @@ iterateChainSucc(AliasAnalysis *AA, const MachineFrameInfo *MFI,
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/// checks whether SU can be aliasing any node dominated
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/// by it.
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static void adjustChainDeps(AliasAnalysis *AA, const MachineFrameInfo *MFI,
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SUnit *SU, SUnit *ExitSU, std::set<SUnit *> &CheckList) {
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SUnit *SU, SUnit *ExitSU, std::set<SUnit *> &CheckList,
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unsigned LatencyToLoad) {
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if (!SU)
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return;
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@ -650,9 +651,11 @@ static void adjustChainDeps(AliasAnalysis *AA, const MachineFrameInfo *MFI,
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I != IE; ++I) {
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if (SU == *I)
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continue;
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if (MIsNeedChainEdge(AA, MFI, SU->getInstr(), (*I)->getInstr()))
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(*I)->addPred(SDep(SU, SDep::Order, /*Latency=*/0, /*Reg=*/0,
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if (MIsNeedChainEdge(AA, MFI, SU->getInstr(), (*I)->getInstr())) {
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unsigned Latency = ((*I)->getInstr()->mayLoad()) ? LatencyToLoad : 0;
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(*I)->addPred(SDep(SU, SDep::Order, Latency, /*Reg=*/0,
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/*isNormalMemory=*/true));
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}
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// Now go through all the chain successors and iterate from them.
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// Keep track of visited nodes.
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for (SUnit::const_succ_iterator J = (*I)->Succs.begin(),
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@ -815,8 +818,7 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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// after stack slots are lowered to actual addresses.
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// TODO: Use an AliasAnalysis and do real alias-analysis queries, and
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// produce more precise dependence information.
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#define STORE_LOAD_LATENCY 1
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unsigned TrueMemOrderLatency = 0;
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unsigned TrueMemOrderLatency = MI->mayStore() ? 1 : 0;
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if (isGlobalMemoryObject(AA, MI)) {
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// Be conservative with these and add dependencies on all memory
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// references, even those that are known to not alias.
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@ -835,7 +837,8 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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BarrierChain = SU;
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// This is a barrier event that acts as a pivotal node in the DAG,
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// so it is safe to clear list of exposed nodes.
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes);
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes,
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TrueMemOrderLatency);
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RejectMemNodes.clear();
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NonAliasMemDefs.clear();
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NonAliasMemUses.clear();
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@ -843,8 +846,13 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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// fall-through
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new_alias_chain:
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// Chain all possibly aliasing memory references though SU.
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if (AliasChain)
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addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes);
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if (AliasChain) {
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unsigned ChainLatency = 0;
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if (AliasChain->getInstr()->mayLoad())
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ChainLatency = TrueMemOrderLatency;
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addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes,
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ChainLatency);
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}
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AliasChain = SU;
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for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
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addChainDependency(AA, MFI, SU, PendingLoads[k], RejectMemNodes,
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@ -858,13 +866,13 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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addChainDependency(AA, MFI, SU, I->second[i], RejectMemNodes,
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TrueMemOrderLatency);
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}
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes);
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes,
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TrueMemOrderLatency);
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PendingLoads.clear();
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AliasMemDefs.clear();
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AliasMemUses.clear();
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} else if (MI->mayStore()) {
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bool MayAlias = true;
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TrueMemOrderLatency = STORE_LOAD_LATENCY;
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if (const Value *V = getUnderlyingObjectForInstr(MI, MFI, MayAlias)) {
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// A store to a specific PseudoSourceValue. Add precise dependencies.
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// Record the def in MemDefs, first adding a dep if there is
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@ -905,7 +913,8 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes);
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// But we also should check dependent instructions for the
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// SU in question.
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes);
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes,
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TrueMemOrderLatency);
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}
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// Add dependence on barrier chain, if needed.
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// There is no point to check aliasing on barrier event. Even if
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@ -927,7 +936,6 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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/*isArtificial=*/true));
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} else if (MI->mayLoad()) {
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bool MayAlias = true;
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TrueMemOrderLatency = 0;
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if (MI->isInvariantLoad(AA)) {
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// Invariant load, no chain dependencies needed!
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} else {
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@ -955,7 +963,7 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
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MayAlias = true;
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}
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if (MayAlias)
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes);
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adjustChainDeps(AA, MFI, SU, &ExitSU, RejectMemNodes, /*Latency=*/0);
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// Add dependencies on alias and barrier chains, if needed.
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if (MayAlias && AliasChain)
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addChainDependency(AA, MFI, SU, AliasChain, RejectMemNodes);
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41
test/CodeGen/ARM/2012-06-12-SchedMemLatency.ll
Normal file
41
test/CodeGen/ARM/2012-06-12-SchedMemLatency.ll
Normal file
@ -0,0 +1,41 @@
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; RUN: llc < %s -o /dev/null "-mtriple=thumbv7-apple-ios" -debug-only=post-RA-sched 2> %t
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; RUN: FileCheck %s < %t
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; REQUIRES: asserts
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; Make sure that mayalias store-load dependencies have one cycle
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; latency regardless of whether they are barriers or not.
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; CHECK: ** List Scheduling
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; CHECK: SU(2){{.*}}STR{{.*}}Volatile
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; CHECK-NOT: ch SU
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; CHECK: ch SU(3): Latency=1
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; CHECK-NOT: ch SU
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; CHECK: SU(3){{.*}}LDR{{.*}}Volatile
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; CHECK-NOT: ch SU
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; CHECK: ch SU(2): Latency=1
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; CHECK-NOT: ch SU
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; CHECK: ** List Scheduling
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; CHECK: SU(2){{.*}}STR{{.*}}
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; CHECK-NOT: ch SU
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; CHECK: ch SU(3): Latency=1
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; CHECK-NOT: ch SU
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; CHECK: SU(3){{.*}}LDR{{.*}}
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; CHECK-NOT: ch SU
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; CHECK: ch SU(2): Latency=1
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; CHECK-NOT: ch SU
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define i32 @f1(i32* nocapture %p1, i32* nocapture %p2) nounwind {
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entry:
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store volatile i32 65540, i32* %p1, align 4, !tbaa !0
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%0 = load volatile i32* %p2, align 4, !tbaa !0
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ret i32 %0
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}
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define i32 @f2(i32* nocapture %p1, i32* nocapture %p2) nounwind {
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entry:
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store i32 65540, i32* %p1, align 4, !tbaa !0
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%0 = load i32* %p2, align 4, !tbaa !0
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ret i32 %0
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}
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!0 = metadata !{metadata !"int", metadata !1}
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!1 = metadata !{metadata !"omnipotent char", metadata !2}
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!2 = metadata !{metadata !"Simple C/C++ TBAA"}
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