[llvm] r327999 - [XRay] Lazily compute MachineLoopInfo instead of requiring it.

[Michael Zolotukhin via llvm-commits]

Author: mzolotukhin
Date: Tue Mar 20 10:02:29 2018
New Revision: 327999

URL: http://llvm.org/viewvc/llvm-project?rev=327999&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp
    llvm/trunk/test/CodeGen/X86/O0-pipeline.ll

Modified: llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp?rev=327999&r1=327998&r2=327999&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp (original)
+++ llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp Tue Mar 20 10:02:29 2018
@@ -52,7 +52,6 @@ struct XRayInstrumentation : public Mach
 
   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::runOnMachineFu
     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.
   }
 

Modified: llvm/trunk/test/CodeGen/X86/O0-pipeline.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/O0-pipeline.ll?rev=327999&r1=327998&r2=327999&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/O0-pipeline.ll (original)
+++ llvm/trunk/test/CodeGen/X86/O0-pipeline.ll Tue Mar 20 10:02:29 2018
@@ -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