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[XRay] Lazily compute MachineLoopInfo instead of requiring it. 

Summary:
Currently X-Ray Instrumentation pass has a dependency on MachineLoopInfo
(and thus on MachineDominatorTree as well) and we have to compute them
even if X-Ray is not used. This patch changes it to a lazy computation
to save compile time by avoiding these redundant computations.

Reviewers: dberris, kubamracek

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D44666

llvm-svn: 327999
This commit is contained in:
Michael Zolotukhin 2018-03-20 17:02:29 +00:00
parent 54b161e47f
commit fb3f509e01
2 changed files with 17 additions and 5 deletions
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20
llvm/lib/CodeGen/XRayInstrumentation.cpp
View File

@ -52,7 +52,6 @@ struct XRayInstrumentation : public MachineFunctionPass {
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
@ -160,11 +159,26 @@ bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
for (const auto &MBB : MF)
MICount += MBB.size();
// Get MachineDominatorTree or compute it on the fly if it's unavailable
auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
MachineDominatorTree ComputedMDT;
if (!MDT) {
ComputedMDT.getBase().recalculate(MF);
MDT = &ComputedMDT;
}
// Get MachineLoopInfo or compute it on the fly if it's unavailable
auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
MachineLoopInfo ComputedMLI;
if (!MLI) {
ComputedMLI.getBase().analyze(MDT->getBase());
MLI = &ComputedMLI;
}
// Check if we have a loop.
// FIXME: Maybe make this smarter, and see whether the loops are dependent
// on inputs or side-effects?
MachineLoopInfo &MLI = getAnalysis<MachineLoopInfo>();
if (MLI.empty() && MICount < XRayThreshold)
if (MLI->empty() && MICount < XRayThreshold)
return false; // Function is too small and has no loops.
}

2
llvm/test/CodeGen/X86/O0-pipeline.ll
View File

@ -55,8 +55,6 @@
; CHECK-NEXT: StackMap Liveness Analysis
; CHECK-NEXT: Live DEBUG_VALUE analysis
; CHECK-NEXT: Insert fentry calls
; CHECK-NEXT: MachineDominator Tree Construction
; CHECK-NEXT: Machine Natural Loop Construction
; CHECK-NEXT: Insert XRay ops
; CHECK-NEXT: Implement the 'patchable-function' attribute
; CHECK-NEXT: X86 Retpoline Thunks