[ctx_prof] Insert the ctx prof flattener after the module inliner (#107499)

This patch enables experimenting with the contextual profile. ICP is currently disabled in this case - will reenable it subsequently. Also subsequently the inline cost model / decision making would be updated to be context-aware. Right now, this just achieves "complete use" of the profile, in that it's ingested, maintained, and sunk to a flat profile when not needed anymore.

Issue [#89287](#89287)

Author: mtrofin

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -25,6 +25,7 @@
 #include "llvm/Analysis/ScopedNoAliasAA.h"
 #include "llvm/Analysis/TypeBasedAliasAnalysis.h"
 #include "llvm/IR/PassManager.h"
+#include "llvm/Pass.h"
 #include "llvm/Passes/OptimizationLevel.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/CommandLine.h"
@@ -1014,6 +1015,11 @@ PassBuilder::buildModuleInlinerPipeline(OptimizationLevel Level,
   IP.EnableDeferral = false;
 
   MPM.addPass(ModuleInlinerPass(IP, UseInlineAdvisor, Phase));
+  if (!UseCtxProfile.empty() && Phase == ThinOrFullLTOPhase::ThinLTOPostLink) {
+    MPM.addPass(GlobalOptPass());
+    MPM.addPass(GlobalDCEPass());
+    MPM.addPass(PGOCtxProfFlatteningPass());
+  }
 
   MPM.addPass(createModuleToFunctionPassAdaptor(
       buildFunctionSimplificationPipeline(Level, Phase),
@@ -1740,11 +1746,14 @@ ModulePassManager PassBuilder::buildThinLTODefaultPipeline(
     MPM.addPass(GlobalDCEPass());
     return MPM;
   }
-
-  // Add the core simplification pipeline.
-  MPM.addPass(buildModuleSimplificationPipeline(
-      Level, ThinOrFullLTOPhase::ThinLTOPostLink));
-
+  if (!UseCtxProfile.empty()) {
+    MPM.addPass(
+        buildModuleInlinerPipeline(Level, ThinOrFullLTOPhase::ThinLTOPostLink));
+  } else {
+    // Add the core simplification pipeline.
+    MPM.addPass(buildModuleSimplificationPipeline(
+        Level, ThinOrFullLTOPhase::ThinLTOPostLink));
+  }
   // Now add the optimization pipeline.
   MPM.addPass(buildModuleOptimizationPipeline(
       Level, ThinOrFullLTOPhase::ThinLTOPostLink));

llvm/lib/Transforms/IPO/ModuleInliner.cpp

@@ -241,8 +241,10 @@ PreservedAnalyses ModuleInlinerPass::run(Module &M,
           // the post-inline cleanup and the next DevirtSCCRepeatedPass
           // iteration because the next iteration may not happen and we may
           // miss inlining it.
-          if (tryPromoteCall(*ICB))
-            NewCallee = ICB->getCalledFunction();
+          // FIXME: enable for ctxprof.
+          if (!CtxProf)
+            if (tryPromoteCall(*ICB))
+              NewCallee = ICB->getCalledFunction();
         }
         if (NewCallee)
           if (!NewCallee->isDeclaration())

llvm/test/Analysis/CtxProfAnalysis/inline.ll

@@ -31,6 +31,23 @@
 ; CHECK-NEXT:    %call2 = call i32 @a(i32 %x) #1
 ; CHECK-NEXT:    br label %exit
 
+; Make sure the postlink thinlto pipeline is aware of ctxprof
+; RUN: opt -passes='thinlto<O2>' -use-ctx-profile=%t/profile.ctxprofdata \
+; RUN:   %t/module.ll -S -o - | FileCheck %s --check-prefix=PIPELINE
+
+; PIPELINE-LABEL: define i32 @entrypoint
+; PIPELINE-SAME: !prof ![[ENTRYPOINT_COUNT:[0-9]+]]
+; PIPELINE-LABEL: loop.i:
+; PIPELINE:         br i1 %cond.i, label %loop.i, label %exit, !prof ![[LOOP_BW_INL:[0-9]+]]
+; PIPELINE-LABEL: define i32 @a
+; PIPELINE-LABEL: loop:
+; PIPELINE:         br i1 %cond, label %loop, label %exit, !prof ![[LOOP_BW_ORIG:[0-9]+]]
+
+; PIPELINE: ![[ENTRYPOINT_COUNT]] = !{!"function_entry_count", i64 10}
+; These are the weights of the inlined @a, where the counters were 2, 100 (2 for entry, 100 for loop)
+; PIPELINE: ![[LOOP_BW_INL]] = !{!"branch_weights", i32 98, i32 2}
+; These are the weights of the un-inlined @a, where the counters were 8, 500 (8 for entry, 500 for loop)
+; PIPELINE: ![[LOOP_BW_ORIG]] = !{!"branch_weights", i32 492, i32 8}
 
 ;--- module.ll
 define i32 @entrypoint(i32 %x) !guid !0 {

llvm/test/Other/opt-hot-cold-split.ll

@@ -2,7 +2,7 @@
 ; RUN: opt -mtriple=x86_64-- -hot-cold-split=true -passes='lto-pre-link<Os>' -debug-pass-manager < %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=LTO-PRELINK-Os
 ; RUN: opt -mtriple=x86_64-- -hot-cold-split=true -passes='thinlto-pre-link<Os>' -debug-pass-manager < %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=THINLTO-PRELINK-Os
 ; RUN: opt -mtriple=x86_64-- -hot-cold-split=true -passes='lto<Os>' -debug-pass-manager < %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=LTO-POSTLINK-Os
-; RUN: opt -mtriple=x86_64-- -hot-cold-split=true -passes='thinlto<Os>' -debug-pass-manager < %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=THINLTO-POSTLINK-Os
+; RUN: opt -mtriple=x86_64-- -hot-cold-split=true -LINK-Os
 
 ; REQUIRES: asserts
 

llvm/test/ThinLTO/X86/ctxprof.ll

@@ -9,13 +9,23 @@
 ; RUN: mkdir -p %t
 ; RUN: split-file %s %t
 ;
-; RUN: opt -module-summary %t/m1.ll -o %t/m1.bc
-; RUN: opt -module-summary %t/m2.ll -o %t/m2.bc
+; RUN: opt -module-summary -passes=assign-guid %t/m1.ll -o %t/m1.bc
+; RUN: opt -module-summary -passes=assign-guid %t/m2.ll -o %t/m2.bc
 ; RUN: llvm-dis %t/m1.bc -o - | FileCheck %s --check-prefix=GUIDS-1
 ; RUN: llvm-dis %t/m2.bc -o - | FileCheck %s --check-prefix=GUIDS-2
 ;
+; GUIDS-1-LABEL: @m1_f1
+; GUIDS-1-SAME: !guid ![[GUID1:[0-9]+]]
+; GUIDS-1:  ![[GUID1]] = !{i64 6019442868614718803}
+; GUIDS-1: ^0 = module:
 ; GUIDS-1: name: "m1_f1"
 ; GUIDS-1-SAME: guid = 6019442868614718803
+
+; note: -2853647799038631862 is 15593096274670919754
+; GUIDS-2-LABEL: @m2_f1
+; GUIDS-2-SAME: !guid ![[GUID2:[0-9]+]]
+; GUIDS-2: ![[GUID2]] = !{i64 -2853647799038631862}
+; GUIDS-2: ^0 = module:
 ; GUIDS-2: name: "m2_f1"
 ; GUIDS-2-SAME: guid = 15593096274670919754
 ;