Provide basic LTO extension points

[serge-sans-paille]

Summary

There is no extension point for LTO passes, this patch provides two basic extension points. They don't apply to ThinLTO but it's a debatable question.

[serge-sans-paille]

@mehdi_amini up :-)

[mehdi_amini]

(Patch is missing context)

Sorry I missed this when you sent it the first time.

I wonder if the LTO pass pipeline shouldn't honor the existing EP_EarlyAsPossible extension point?

[serge-sans-paille]

Diff updated with context

[serge-sans-paille]

I wonder if the LTO pass pipeline shouldn't honor the existing EP_EarlyAsPossible extension point?

EP_EarlyAsPossible is referenced by populateFunctionPassManager which seems to be called wathever the optimization level, but maybe you're proposing to have it applied twice, once for compilation unit level, and once for link level?
If that's the case, I find it confusing, and EP_LinkTimeOptimizationEarly would play that role.

[serge-sans-paille]

@mehdi_amini up :-)

[serge-sans-paille]

@mehdi_amini up ;-)

[mehdi_amini]

Sorry I missed the previous updates.

llvm/include/llvm/Transforms/IPO/PassManagerBuilder.h

122 ↗

(On Diff #202377)

I think FullLTO should appear in the name to make it clear that it does not apply to thin

[xbolva00]

This seems interesting, maybe you could add more docs/tutorial how to use it? :)
And possibly mention it in release news ?

llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h

enum ExtensionPointTy {
     /// This is the place to add passes that can remove loops, such as target-
     /// specific loop idiom recognition.
     EP_LateLoopOptimizations,
 
     /// EP_CGSCCOptimizerLate - This extension point allows adding CallGraphSCC
     /// passes at the end of the main CallGraphSCC passes and before any
     /// function simplification passes run by CGPassManager.
     EP_CGSCCOptimizerLate,
+
+    /// EP_FullLinkTimeOptimizationEarly - This extensions point allow adding
+    /// passes that
+    /// run at Link Time, before Full Link Time Optimization.
+    EP_FullLinkTimeOptimizationEarly,
+
+    /// EP_FullLinkTimeOptimizationLast - This extensions point allow adding
+    /// passes that
+    /// run at Link Time, after Full Link Time Optimization.
+    EP_FullLinkTimeOptimizationLast,
   };
 
   /// The Optimization Level - Specify the basic optimization level.
   ///    0 = -O0, 1 = -O1, 2 = -O2, 3 = -O3
   unsigned OptLevel;
 
   /// SizeLevel - How much we're optimizing for size.
   ///    0 = none, 1 = -Os, 2 = -Oz

llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp

 
 void PassManagerBuilder::populateLTOPassManager(legacy::PassManagerBase &PM) {
   if (LibraryInfo)
     PM.add(new TargetLibraryInfoWrapperPass(*LibraryInfo));
 
   if (VerifyInput)
     PM.add(createVerifierPass());
 
+  addExtensionsToPM(EP_FullLinkTimeOptimizationEarly, PM);
+
   if (OptLevel != 0)
     addLTOOptimizationPasses(PM);
   else {
     // The whole-program-devirt pass needs to run at -O0 because only it knows
     // about the llvm.type.checked.load intrinsic: it needs to both lower the
     // intrinsic itself and handle it in the summary.
     PM.add(createWholeProgramDevirtPass(ExportSummary, nullptr));
   }
 
   // Create a function that performs CFI checks for cross-DSO calls with targets
   // in the current module.
   PM.add(createCrossDSOCFIPass());
 
   // Lower type metadata and the type.test intrinsic. This pass supports Clang's
   // control flow integrity mechanisms (-fsanitize=cfi*) and needs to run at
   // link time if CFI is enabled. The pass does nothing if CFI is disabled.
   PM.add(createLowerTypeTestsPass(ExportSummary, nullptr));
 
   if (OptLevel != 0)
     addLateLTOOptimizationPasses(PM);
 
+  addExtensionsToPM(EP_FullLinkTimeOptimizationLast, PM);
+
   if (VerifyOutput)
     PM.add(createVerifierPass());
 }
 
 inline PassManagerBuilder *unwrap(LLVMPassManagerBuilderRef P) {
     return reinterpret_cast<PassManagerBuilder*>(P);
 }