[llvm-branch-commits] [llvm] [StaticDataLayout] Factor out a helper function for section prefix eligibility and use it in both optimizer and codegen (PR #162348)
Mingming Liu via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Tue Oct 7 14:45:24 PDT 2025
https://github.com/mingmingl-llvm updated https://github.com/llvm/llvm-project/pull/162348
>From f68b06f65609078d7e1c788e95d78fab397e4966 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 7 Oct 2025 11:59:13 -0700
Subject: [PATCH 1/3] [nfc][StaticDataLayout]Add helper functions to tell the
eligibility status of a global variable for section prefix annotation
---
.../llvm/Analysis/StaticDataProfileInfo.h | 18 +++++++++
llvm/lib/Analysis/StaticDataProfileInfo.cpp | 37 +++++++++++++++++++
llvm/lib/CodeGen/StaticDataAnnotator.cpp | 15 +-------
.../Transforms/Instrumentation/MemProfUse.cpp | 30 ++++-----------
4 files changed, 65 insertions(+), 35 deletions(-)
diff --git a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
index fa21eba1377df..f06e7ceaa74ce 100644
--- a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
+++ b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
@@ -10,6 +10,24 @@
namespace llvm {
+namespace memprof {
+// Represents the eligibility status of a global variable for section prefix
+// annotation. Other than AnnotationOk, each enum value indicates a specific
+// reason for ineligibility.
+enum class AnnotationKind : uint8_t {
+ AnnotationOK,
+ DeclForLinker,
+ ExplicitSection,
+ ReservedName,
+};
+/// Returns the annotation kind of the global variable \p GV.
+AnnotationKind getAnnotationKind(const GlobalVariable &GV);
+
+/// Returns true if the annotation kind of the global variable \p GV is
+/// AnnotationOK.
+bool IsAnnotationOK(const GlobalVariable &GV);
+} // namespace memprof
+
/// A class that holds the constants that represent static data and their
/// profile information and provides methods to operate on them.
class StaticDataProfileInfo {
diff --git a/llvm/lib/Analysis/StaticDataProfileInfo.cpp b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
index b036b2dde770e..ff4582ca7eeb1 100644
--- a/llvm/lib/Analysis/StaticDataProfileInfo.cpp
+++ b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
@@ -6,6 +6,43 @@
#include "llvm/ProfileData/InstrProf.h"
using namespace llvm;
+
+namespace llvm {
+namespace memprof {
+// Returns true iff the global variable has custom section either by
+// __attribute__((section("name")))
+// (https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate)
+// or #pragma clang section directives
+// (https://clang.llvm.org/docs/LanguageExtensions.html#specifying-section-names-for-global-objects-pragma-clang-section).
+static bool hasExplicitSectionName(const GlobalVariable &GVar) {
+ if (GVar.hasSection())
+ return true;
+
+ auto Attrs = GVar.getAttributes();
+ if (Attrs.hasAttribute("bss-section") || Attrs.hasAttribute("data-section") ||
+ Attrs.hasAttribute("relro-section") ||
+ Attrs.hasAttribute("rodata-section"))
+ return true;
+ return false;
+}
+
+AnnotationKind getAnnotationKind(const GlobalVariable &GV) {
+ if (GV.isDeclarationForLinker())
+ return AnnotationKind::DeclForLinker;
+ StringRef Name = GV.getName();
+ if (Name.starts_with("llvm."))
+ return AnnotationKind::ReservedName;
+ if (hasExplicitSectionName(GV))
+ return AnnotationKind::ExplicitSection;
+ return AnnotationKind::AnnotationOK;
+}
+
+bool IsAnnotationOK(const GlobalVariable &GV) {
+ return getAnnotationKind(GV) == AnnotationKind::AnnotationOK;
+}
+} // namespace memprof
+} // namespace llvm
+
void StaticDataProfileInfo::addConstantProfileCount(
const Constant *C, std::optional<uint64_t> Count) {
if (!Count) {
diff --git a/llvm/lib/CodeGen/StaticDataAnnotator.cpp b/llvm/lib/CodeGen/StaticDataAnnotator.cpp
index 53a9ab4dbda02..9a68ee96ab056 100644
--- a/llvm/lib/CodeGen/StaticDataAnnotator.cpp
+++ b/llvm/lib/CodeGen/StaticDataAnnotator.cpp
@@ -75,22 +75,11 @@ bool StaticDataAnnotator::runOnModule(Module &M) {
bool Changed = false;
for (auto &GV : M.globals()) {
- if (GV.isDeclarationForLinker())
+ if (!llvm::memprof::IsAnnotationOK(GV))
continue;
- // The implementation below assumes prior passes don't set section prefixes,
- // and specifically do 'assign' rather than 'update'. So report error if a
- // section prefix is already set.
- if (auto maybeSectionPrefix = GV.getSectionPrefix();
- maybeSectionPrefix && !maybeSectionPrefix->empty())
- llvm::report_fatal_error("Global variable " + GV.getName() +
- " already has a section prefix " +
- *maybeSectionPrefix);
-
StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI);
- if (SectionPrefix.empty())
- continue;
-
+ // setSectionPrefix returns true if the section prefix is changed.
Changed |= GV.setSectionPrefix(SectionPrefix);
}
diff --git a/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp b/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
index d86fcf268ce4f..ca2af1a9534d3 100644
--- a/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
@@ -17,6 +17,7 @@
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/MemoryProfileInfo.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/Analysis/StaticDataProfileInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Function.h"
@@ -775,23 +776,6 @@ PreservedAnalyses MemProfUsePass::run(Module &M, ModuleAnalysisManager &AM) {
return PreservedAnalyses::none();
}
-// Returns true iff the global variable has custom section either by
-// __attribute__((section("name")))
-// (https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate)
-// or #pragma clang section directives
-// (https://clang.llvm.org/docs/LanguageExtensions.html#specifying-section-names-for-global-objects-pragma-clang-section).
-static bool hasExplicitSectionName(const GlobalVariable &GVar) {
- if (GVar.hasSection())
- return true;
-
- auto Attrs = GVar.getAttributes();
- if (Attrs.hasAttribute("bss-section") || Attrs.hasAttribute("data-section") ||
- Attrs.hasAttribute("relro-section") ||
- Attrs.hasAttribute("rodata-section"))
- return true;
- return false;
-}
-
bool MemProfUsePass::annotateGlobalVariables(
Module &M, const memprof::DataAccessProfData *DataAccessProf) {
if (!AnnotateStaticDataSectionPrefix || M.globals().empty())
@@ -817,13 +801,16 @@ bool MemProfUsePass::annotateGlobalVariables(
for (GlobalVariable &GVar : M.globals()) {
assert(!GVar.getSectionPrefix().has_value() &&
"GVar shouldn't have section prefix yet");
- if (GVar.isDeclarationForLinker())
- continue;
-
- if (hasExplicitSectionName(GVar)) {
+ auto Kind = llvm::memprof::getAnnotationKind(GVar);
+ switch (Kind) {
+ case llvm::memprof::AnnotationKind::AnnotationOK:
+ break;
+ case llvm::memprof::AnnotationKind::ExplicitSection:
++NumOfMemProfExplicitSectionGlobalVars;
LLVM_DEBUG(dbgs() << "Global variable " << GVar.getName()
<< " has explicit section name. Skip annotating.\n");
+ [[fallthrough]];
+ default:
continue;
}
@@ -833,7 +820,6 @@ bool MemProfUsePass::annotateGlobalVariables(
// TODO: Track string content hash in the profiles and compute it inside the
// compiler to categeorize the hotness string literals.
if (Name.starts_with(".str")) {
-
LLVM_DEBUG(dbgs() << "Skip annotating string literal " << Name << "\n");
continue;
}
>From 331888be493563f8446e17ce670af7ceebffb025 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 7 Oct 2025 12:20:49 -0700
Subject: [PATCH 2/3] save irrelevant change for the next PR to make this one
focused
---
llvm/lib/CodeGen/StaticDataAnnotator.cpp | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/llvm/lib/CodeGen/StaticDataAnnotator.cpp b/llvm/lib/CodeGen/StaticDataAnnotator.cpp
index 9a68ee96ab056..9b737751c4a98 100644
--- a/llvm/lib/CodeGen/StaticDataAnnotator.cpp
+++ b/llvm/lib/CodeGen/StaticDataAnnotator.cpp
@@ -78,8 +78,19 @@ bool StaticDataAnnotator::runOnModule(Module &M) {
if (!llvm::memprof::IsAnnotationOK(GV))
continue;
+ // The implementation below assumes prior passes don't set section prefixes,
+ // and specifically do 'assign' rather than 'update'. So report error if a
+ // section prefix is already set.
+ if (auto maybeSectionPrefix = GV.getSectionPrefix();
+ maybeSectionPrefix && !maybeSectionPrefix->empty())
+ llvm::report_fatal_error("Global variable " + GV.getName() +
+ " already has a section prefix " +
+ *maybeSectionPrefix);
+
StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI);
- // setSectionPrefix returns true if the section prefix is changed.
+ if (SectionPrefix.empty())
+ continue;
+
Changed |= GV.setSectionPrefix(SectionPrefix);
}
>From dcb9f001398ebffb2b829092f07c6c8cbc33941a Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 7 Oct 2025 14:38:57 -0700
Subject: [PATCH 3/3] resolve comments
---
llvm/lib/Analysis/StaticDataProfileInfo.cpp | 3 +++
llvm/lib/CodeGen/StaticDataSplitter.cpp | 6 ++----
2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Analysis/StaticDataProfileInfo.cpp b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
index ff4582ca7eeb1..1f751ee5e09d9 100644
--- a/llvm/lib/Analysis/StaticDataProfileInfo.cpp
+++ b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
@@ -29,9 +29,12 @@ static bool hasExplicitSectionName(const GlobalVariable &GVar) {
AnnotationKind getAnnotationKind(const GlobalVariable &GV) {
if (GV.isDeclarationForLinker())
return AnnotationKind::DeclForLinker;
+ // Skip 'llvm.'-prefixed global variables conservatively because they are
+ // often handled specially,
StringRef Name = GV.getName();
if (Name.starts_with("llvm."))
return AnnotationKind::ReservedName;
+ // Respect user-specified custom data sections.
if (hasExplicitSectionName(GV))
return AnnotationKind::ExplicitSection;
return AnnotationKind::AnnotationOK;
diff --git a/llvm/lib/CodeGen/StaticDataSplitter.cpp b/llvm/lib/CodeGen/StaticDataSplitter.cpp
index e22dc2507d548..1593a401bcb24 100644
--- a/llvm/lib/CodeGen/StaticDataSplitter.cpp
+++ b/llvm/lib/CodeGen/StaticDataSplitter.cpp
@@ -130,10 +130,8 @@ StaticDataSplitter::getConstant(const MachineOperand &Op,
if (Op.isGlobal()) {
// Find global variables with local linkage.
const GlobalVariable *GV = getLocalLinkageGlobalVariable(Op.getGlobal());
- // Skip 'llvm.'-prefixed global variables conservatively because they are
- // often handled specially, and skip those not in static data
- // sections.
- if (!GV || GV->getName().starts_with("llvm.") ||
+ // Skip those not eligible for annotation or not in static data sections.
+ if (!GV || !llvm::memprof::IsAnnotationOK(*GV) ||
!inStaticDataSection(*GV, TM))
return nullptr;
return GV;
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