[FuncSpec] Enable it only with -O3

Function specialisation was running at all optimisation levels (if enabled on
the command line, it is not on by default). 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.

Differential Revision: https://reviews.llvm.org/D112129

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f0f7803..8274aee 100644 (file)
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -832,7 +832,7 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
     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
@@ -1406,7 +1406,7 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
     MPM.addPass(PGOIndirectCallPromotion(
         true /* InLTO */, PGOOpt && PGOOpt->Action == PGOOptions::SampleUse));
 
-    if (EnableFunctionSpecialization)
+    if (EnableFunctionSpecialization && Level == OptimizationLevel::O3)
       MPM.addPass(FunctionSpecializationPass());
     // Propagate constants at call sites into the functions they call.  This
     // opens opportunities for globalopt (and inlining) by substituting function

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index f0b5589..74f6853 100644 (file)
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -1017,7 +1017,7 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
         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