Add IR Profile-Guided Optimization (IR PGO) support to the Flang compiler (#136098)

This patch implements IR-based Profile-Guided Optimization support in
Flang through the following flags:

- `-fprofile-generate` for instrumentation-based profile generation

- `-fprofile-use=<dir>/file` for profile-guided optimization

Resolves #74216 (implements IR PGO support phase)

**Key changes:**

- Frontend flag handling aligned with Clang/GCC semantics

- Instrumentation hooks into LLVM PGO infrastructure

- LIT tests verifying:

    - Instrumentation metadata generation

    - Profile loading from specified path

    - Branch weight attribution (IR checks)

**Tests:**

- Added gcc-flag-compatibility.f90 test module verifying:

    -  Flag parsing boundary conditions

    -  IR-level profile annotation consistency

    -  Profile input path normalization rules

- SPEC2006 benchmark results will be shared in comments

For details on LLVM's PGO framework, refer to [Clang PGO
Documentation](https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization).

This implementation was developed by [XSCC Compiler
Team](https://github.com/orgs/OpenXiangShan/teams/xscc).

---------

Co-authored-by: ict-ql <168183727+ict-ql@users.noreply.github.com>
Co-authored-by: Tom Eccles <t@freedommail.info>

1 files changed, 18 insertions, 24 deletions

diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index cd5fc48..03e10b1 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -123,17 +123,10 @@ namespace clang {
 extern llvm::cl::opt<bool> ClSanitizeGuardChecks;
 }
 
-// Default filename used for profile generation.
-static std::string getDefaultProfileGenName() {
-  return DebugInfoCorrelate || ProfileCorrelate != InstrProfCorrelator::NONE
-             ? "default_%m.proflite"
-             : "default_%m.profraw";
-}
-
 // Path and name of file used for profile generation
 static std::string getProfileGenName(const CodeGenOptions &CodeGenOpts) {
   std::string FileName = CodeGenOpts.InstrProfileOutput.empty()
-                             ? getDefaultProfileGenName()
+                             ? llvm::driver::getDefaultProfileGenName()
                              : CodeGenOpts.InstrProfileOutput;
   if (CodeGenOpts.ContinuousProfileSync)
     FileName = "%c" + FileName;
@@ -835,12 +828,12 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
 
   if (CodeGenOpts.hasProfileIRInstr())
     // -fprofile-generate.
-    PGOOpt = PGOOptions(getProfileGenName(CodeGenOpts), "", "",
-                        CodeGenOpts.MemoryProfileUsePath, nullptr,
-                        PGOOptions::IRInstr, PGOOptions::NoCSAction,
-                        ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling,
-                        /*PseudoProbeForProfiling=*/false,
-                        CodeGenOpts.AtomicProfileUpdate);
+    PGOOpt = PGOOptions(
+        getProfileGenName(CodeGenOpts), "", "",
+        CodeGenOpts.MemoryProfileUsePath, nullptr, PGOOptions::IRInstr,
+        PGOOptions::NoCSAction, llvm::ClPGOColdFuncAttr,
+        CodeGenOpts.DebugInfoForProfiling,
+        /*PseudoProbeForProfiling=*/false, CodeGenOpts.AtomicProfileUpdate);
   else if (CodeGenOpts.hasProfileIRUse()) {
     // -fprofile-use.
     auto CSAction = CodeGenOpts.hasProfileCSIRUse() ? PGOOptions::CSIRUse
@@ -848,31 +841,32 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
     PGOOpt = PGOOptions(CodeGenOpts.ProfileInstrumentUsePath, "",
                         CodeGenOpts.ProfileRemappingFile,
                         CodeGenOpts.MemoryProfileUsePath, VFS,
-                        PGOOptions::IRUse, CSAction, ClPGOColdFuncAttr,
+                        PGOOptions::IRUse, CSAction, llvm::ClPGOColdFuncAttr,
                         CodeGenOpts.DebugInfoForProfiling);
   } else if (!CodeGenOpts.SampleProfileFile.empty())
     // -fprofile-sample-use
     PGOOpt = PGOOptions(
         CodeGenOpts.SampleProfileFile, "", CodeGenOpts.ProfileRemappingFile,
         CodeGenOpts.MemoryProfileUsePath, VFS, PGOOptions::SampleUse,
-        PGOOptions::NoCSAction, ClPGOColdFuncAttr,
+        PGOOptions::NoCSAction, llvm::ClPGOColdFuncAttr,
         CodeGenOpts.DebugInfoForProfiling, CodeGenOpts.PseudoProbeForProfiling);
   else if (!CodeGenOpts.MemoryProfileUsePath.empty())
     // -fmemory-profile-use (without any of the above options)
-    PGOOpt = PGOOptions("", "", "", CodeGenOpts.MemoryProfileUsePath, VFS,
-                        PGOOptions::NoAction, PGOOptions::NoCSAction,
-                        ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling);
-  else if (CodeGenOpts.PseudoProbeForProfiling)
-    // -fpseudo-probe-for-profiling
     PGOOpt =
-        PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
+        PGOOptions("", "", "", CodeGenOpts.MemoryProfileUsePath, VFS,
                    PGOOptions::NoAction, PGOOptions::NoCSAction,
-                   ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling, true);
+                   llvm::ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling);
+  else if (CodeGenOpts.PseudoProbeForProfiling)
+    // -fpseudo-probe-for-profiling
+    PGOOpt = PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
+                        PGOOptions::NoAction, PGOOptions::NoCSAction,
+                        llvm::ClPGOColdFuncAttr,
+                        CodeGenOpts.DebugInfoForProfiling, true);
   else if (CodeGenOpts.DebugInfoForProfiling)
     // -fdebug-info-for-profiling
     PGOOpt = PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
                         PGOOptions::NoAction, PGOOptions::NoCSAction,
-                        ClPGOColdFuncAttr, true);
+                        llvm::ClPGOColdFuncAttr, true);
 
   // Check to see if we want to generate a CS profile.
   if (CodeGenOpts.hasProfileCSIRInstr()) {