[PATCH] D112129: [FuncSpec] Enable it only with -O3

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer created this revision.
SjoerdMeijer added reviewers: ChuanqiXu, snehasish, aeubanks, nikic.
Herald added subscribers: ormris, hiraditya.
SjoerdMeijer requested review of this revision.
Herald added a project: LLVM.

Looks like function specialisation was running at all optimisation levels (if enabled on the command line, it is not on by default). I think that was an oversight and not something we want to do. Function specialisation duplicates functions when it triggers, so the backend is processing more functions/instructions resulting in compile-time increases, which seems more appropriate with -O3 and inline with GCC.

Please note that since function specialisation is not enabled by default, this didn't require updating any pass manager tests.


https://reviews.llvm.org/D112129

Files:
  llvm/lib/Passes/PassBuilderPipelines.cpp
  llvm/lib/Transforms/IPO/PassManagerBuilder.cpp


Index: llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -1017,7 +1017,7 @@
         createPGOIndirectCallPromotionLegacyPass(true, !PGOSampleUse.empty()));
 
     // Propage constant function arguments by specializing the functions.
-    if (EnableFunctionSpecialization)
+    if (EnableFunctionSpecialization && OptLevel > 2)
       PM.add(createFunctionSpecializationPass());
 
     // Propagate constants at call sites into the functions they call.  This
Index: llvm/lib/Passes/PassBuilderPipelines.cpp
===================================================================
--- llvm/lib/Passes/PassBuilderPipelines.cpp
+++ llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -832,7 +832,7 @@
     C(MPM, Level);
 
   // Specialize functions with IPSCCP.
-  if (EnableFunctionSpecialization)
+  if (EnableFunctionSpecialization && Level == OptimizationLevel::O3)
     MPM.addPass(FunctionSpecializationPass());
 
   // Interprocedural constant propagation now that basic cleanup has occurred
@@ -1399,7 +1399,7 @@
     MPM.addPass(PGOIndirectCallPromotion(
         true /* InLTO */, PGOOpt && PGOOpt->Action == PGOOptions::SampleUse));
 
-    if (EnableFunctionSpecialization)
+    if (EnableFunctionSpecialization && Level.getSpeedupLevel() > 2)
       MPM.addPass(FunctionSpecializationPass());
     // Propagate constants at call sites into the functions they call.  This
     // opens opportunities for globalopt (and inlining) by substituting function


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