[llvm] 3fd1902 - [FuncSpec] Enable it only with -O3

[Sjoerd Meijer via llvm-commits]

Author: Sjoerd Meijer
Date: 2021-11-04T13:59:00Z
New Revision: 3fd1902ad8ebfaecc57e68aaa6620332dda8d5f9

URL: https://github.com/llvm/llvm-project/commit/3fd1902ad8ebfaecc57e68aaa6620332dda8d5f9
DIFF: https://github.com/llvm/llvm-project/commit/3fd1902ad8ebfaecc57e68aaa6620332dda8d5f9.diff

LOG: [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

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f0f7803ed3ae5..8274aeeaab011 100644
--- 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 f0b5589347e2e..74f68531b89a7 100644
--- 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