[llvm] 1cec6be - [StaticDataLayout] Reconcile data hotness based on PGO counters and data access profiles (#163325)
via llvm-commits
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Wed Oct 15 10:24:14 PDT 2025
Author: Mingming Liu
Date: 2025-10-15T10:24:09-07:00
New Revision: 1cec6be8d6783d94f7e70ea157ecc0563cf11ee8
URL: https://github.com/llvm/llvm-project/commit/1cec6be8d6783d94f7e70ea157ecc0563cf11ee8
DIFF: https://github.com/llvm/llvm-project/commit/1cec6be8d6783d94f7e70ea157ecc0563cf11ee8.diff
LOG: [StaticDataLayout] Reconcile data hotness based on PGO counters and data access profiles (#163325)
This PR enhances the `StaticDataProfileInfo::getConstantSectionPrefix`
pass to reconcile data hotness information from both PGO counters and
data access profiles. When both profiles are available for a global
variable, the pass will now use the "hotter" of the two to determine the
variable's section placement.
This is a follow-up patch of
https://github.com/llvm/llvm-project/pull/162388
Added:
Modified:
llvm/include/llvm/Analysis/StaticDataProfileInfo.h
llvm/lib/Analysis/StaticDataProfileInfo.cpp
llvm/test/CodeGen/X86/global-variable-partition-with-dap.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
index bb7f3be2e8d90..ac03137c93610 100644
--- a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
+++ b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
@@ -60,11 +60,18 @@ class StaticDataProfileInfo {
LLVM_ABI StaticDataHotness getConstantHotnessUsingProfileCount(
const Constant *C, const ProfileSummaryInfo *PSI, uint64_t Count) const;
+ /// Return the hotness based on section prefix \p SectionPrefix.
+ LLVM_ABI StaticDataHotness getSectionHotnessUsingDataAccessProfile(
+ std::optional<StringRef> SectionPrefix) const;
+
/// Return the string representation of the hotness enum \p Hotness.
LLVM_ABI StringRef hotnessToStr(StaticDataHotness Hotness) const;
+ bool EnableDataAccessProf = false;
+
public:
- StaticDataProfileInfo() = default;
+ StaticDataProfileInfo(bool EnableDataAccessProf)
+ : EnableDataAccessProf(EnableDataAccessProf) {}
/// If \p Count is not nullopt, add it to the profile count of the constant \p
/// C in a saturating way, and clamp the count to \p getInstrMaxCountValue if
@@ -73,14 +80,10 @@ class StaticDataProfileInfo {
LLVM_ABI void addConstantProfileCount(const Constant *C,
std::optional<uint64_t> Count);
- /// Return a section prefix for the constant \p C based on its profile count.
- /// - If a constant doesn't have a counter, return an empty string.
- /// - Otherwise,
- /// - If it has a hot count, return "hot".
- /// - If it is seen by unprofiled function, return an empty string.
- /// - If it has a cold count, return "unlikely".
- /// - Otherwise (e.g. it's used by lukewarm functions), return an empty
- /// string.
+ /// Given a constant \p C, returns a section prefix.
+ /// If \p C is a global variable, the section prefix is the bigger one
+ /// between its existing section prefix and its use profile count. Otherwise,
+ /// the section prefix is based on its use profile count.
LLVM_ABI StringRef getConstantSectionPrefix(
const Constant *C, const ProfileSummaryInfo *PSI) const;
};
diff --git a/llvm/lib/Analysis/StaticDataProfileInfo.cpp b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
index e7f0b2c15d604..61d49350c7702 100644
--- a/llvm/lib/Analysis/StaticDataProfileInfo.cpp
+++ b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
@@ -1,10 +1,14 @@
#include "llvm/Analysis/StaticDataProfileInfo.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/ProfileData/InstrProf.h"
+#define DEBUG_TYPE "static-data-profile-info"
+
using namespace llvm;
namespace llvm {
@@ -79,6 +83,17 @@ StaticDataProfileInfo::getConstantHotnessUsingProfileCount(
return StaticDataHotness::LukewarmOrUnknown;
}
+StaticDataProfileInfo::StaticDataHotness
+StaticDataProfileInfo::getSectionHotnessUsingDataAccessProfile(
+ std::optional<StringRef> MaybeSectionPrefix) const {
+ if (!MaybeSectionPrefix)
+ return StaticDataHotness::LukewarmOrUnknown;
+ StringRef Prefix = *MaybeSectionPrefix;
+ assert((Prefix == "hot" || Prefix == "unlikely") &&
+ "Expect section_prefix to be one of hot or unlikely");
+ return Prefix == "hot" ? StaticDataHotness::Hot : StaticDataHotness::Cold;
+}
+
StringRef StaticDataProfileInfo::hotnessToStr(StaticDataHotness Hotness) const {
switch (Hotness) {
case StaticDataHotness::Cold:
@@ -101,13 +116,66 @@ StaticDataProfileInfo::getConstantProfileCount(const Constant *C) const {
StringRef StaticDataProfileInfo::getConstantSectionPrefix(
const Constant *C, const ProfileSummaryInfo *PSI) const {
std::optional<uint64_t> Count = getConstantProfileCount(C);
+
+#ifndef NDEBUG
+ auto DbgPrintPrefix = [](StringRef Prefix) {
+ return Prefix.empty() ? "<empty>" : Prefix;
+ };
+#endif
+
+ if (EnableDataAccessProf) {
+ // Module flag `HasDataAccessProf` is 1 -> empty section prefix means
+ // unknown hotness except for string literals.
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(C);
+ GV && llvm::memprof::IsAnnotationOK(*GV) &&
+ !GV->getName().starts_with(".str")) {
+ auto HotnessFromDataAccessProf =
+ getSectionHotnessUsingDataAccessProfile(GV->getSectionPrefix());
+
+ if (!Count) {
+ StringRef Prefix = hotnessToStr(HotnessFromDataAccessProf);
+ LLVM_DEBUG(dbgs() << GV->getName() << " has section prefix "
+ << DbgPrintPrefix(Prefix)
+ << ", solely from data access profiles\n");
+ return Prefix;
+ }
+
+ // Both data access profiles and PGO counters are available. Use the
+ // hotter one.
+ auto HotnessFromPGO = getConstantHotnessUsingProfileCount(C, PSI, *Count);
+ StaticDataHotness GlobalVarHotness = StaticDataHotness::LukewarmOrUnknown;
+ if (HotnessFromDataAccessProf == StaticDataHotness::Hot ||
+ HotnessFromPGO == StaticDataHotness::Hot) {
+ GlobalVarHotness = StaticDataHotness::Hot;
+ } else if (HotnessFromDataAccessProf ==
+ StaticDataHotness::LukewarmOrUnknown ||
+ HotnessFromPGO == StaticDataHotness::LukewarmOrUnknown) {
+ GlobalVarHotness = StaticDataHotness::LukewarmOrUnknown;
+ } else {
+ GlobalVarHotness = StaticDataHotness::Cold;
+ }
+ StringRef Prefix = hotnessToStr(GlobalVarHotness);
+ LLVM_DEBUG(
+ dbgs() << GV->getName() << " has section prefix "
+ << DbgPrintPrefix(Prefix)
+ << ", the max from data access profiles as "
+ << DbgPrintPrefix(hotnessToStr(HotnessFromDataAccessProf))
+ << " and PGO counters as "
+ << DbgPrintPrefix(hotnessToStr(HotnessFromPGO)) << "\n");
+ return Prefix;
+ }
+ }
if (!Count)
return "";
return hotnessToStr(getConstantHotnessUsingProfileCount(C, PSI, *Count));
}
bool StaticDataProfileInfoWrapperPass::doInitialization(Module &M) {
- Info.reset(new StaticDataProfileInfo());
+ bool EnableDataAccessProf = false;
+ if (auto *MD = mdconst::extract_or_null<ConstantInt>(
+ M.getModuleFlag("EnableDataAccessProf")))
+ EnableDataAccessProf = MD->getZExtValue();
+ Info.reset(new StaticDataProfileInfo(EnableDataAccessProf));
return false;
}
diff --git a/llvm/test/CodeGen/X86/global-variable-partition-with-dap.ll b/llvm/test/CodeGen/X86/global-variable-partition-with-dap.ll
index f3950b75a969f..b2b0a6dab843f 100644
--- a/llvm/test/CodeGen/X86/global-variable-partition-with-dap.ll
+++ b/llvm/test/CodeGen/X86/global-variable-partition-with-dap.ll
@@ -1,17 +1,101 @@
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
-;; A minimal test case. Subsequent PRs will expand on this test case
-;; (e.g., with more functions, variables and profiles) and test the hotness
-;; reconcillation implementation.
+;; Requires asserts for -debug-only.
+; REQUIRES: asserts
+
+; RUN: rm -rf %t && split-file %s %t && cd %t
+
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu -relocation-model=pic \
+; RUN: -partition-static-data-sections=true \
+; RUN: -debug-only=static-data-profile-info \
+; RUN: -data-sections=true -unique-section-names=false \
+; RUN: input-with-data-access-prof-on.ll -o - 2>&1 | FileCheck %s --check-prefixes=LOG,IR
+
; RUN: llc -mtriple=x86_64-unknown-linux-gnu -relocation-model=pic \
; RUN: -partition-static-data-sections=true \
+; RUN: -debug-only=static-data-profile-info \
; RUN: -data-sections=true -unique-section-names=false \
-; RUN: %s -o - 2>&1 | FileCheck %s --check-prefix=IR
+; RUN: input-with-data-access-prof-off.ll -o - 2>&1 | FileCheck %s --check-prefixes=OFF
+
+; LOG: hot_bss has section prefix hot, the max from data access profiles as hot and PGO counters as hot
+; LOG: data_unknown_hotness has section prefix <empty>, the max from data access profiles as <empty> and PGO counters as unlikely
+; LOG: external_relro_array has section prefix unlikely, solely from data access profiles
+
+; IR: .type hot_bss, at object
+; IR-NEXT: .section .bss.hot.,"aw"
+; IR: .type data_unknown_hotness, at object
+; IR-NEXT: .section .data,"aw"
+; IR: .type external_relro_array, at object
+; IR-NEXT: .section .data.rel.ro.unlikely.,"aw"
+
+
+; OFF: .type hot_bss, at object
+; OFF-NEXT: .section .bss.hot.,"aw"
+; OFF: .type data_unknown_hotness, at object
+; OFF-NEXT: .section .data.unlikely.,"aw"
+;; Global variable section prefix metadata is not used when
+;; module flag `EnableDataAccessProf` is 0, and @external_relro_array has
+;; external linkage, so analysis based on PGO counters doesn't apply.
+; OFF: .type external_relro_array, at object # @external_relro_array
+; OFF-NEXT: .section .data.rel.ro,"aw"
+
+;--- input-with-data-access-prof-on.ll
+; Internal vars
+ at hot_bss = internal global i32 0, !section_prefix !17
+ at data_unknown_hotness = internal global i32 1
+; External vars
+ at external_relro_array = constant [2 x ptr] [ptr @hot_bss, ptr @data_unknown_hotness], !section_prefix !18
+
+define void @cold_func() !prof !15 {
+ %9 = load i32, ptr @data_unknown_hotness
+ %11 = call i32 (...) @func_taking_arbitrary_param(i32 %9)
+ ret void
+}
+
+define void @hot_func() !prof !14 {
+ %9 = load i32, ptr @hot_bss
+ %11 = call i32 (...) @func_taking_arbitrary_param(i32 %9)
+ ret void
+}
+
+declare i32 @func_taking_arbitrary_param(...)
-; IR: .section .bss.hot.,"aw"
+!llvm.module.flags = !{!0, !1}
+!0 = !{i32 2, !"EnableDataAccessProf", i32 1}
+!1 = !{i32 1, !"ProfileSummary", !2}
+!2 = !{!3, !4, !5, !6, !7, !8, !9, !10}
+!3 = !{!"ProfileFormat", !"InstrProf"}
+!4 = !{!"TotalCount", i64 1460183}
+!5 = !{!"MaxCount", i64 849024}
+!6 = !{!"MaxInternalCount", i64 32769}
+!7 = !{!"MaxFunctionCount", i64 849024}
+!8 = !{!"NumCounts", i64 23627}
+!9 = !{!"NumFunctions", i64 3271}
+!10 = !{!"DetailedSummary", !11}
+!11 = !{!12, !13}
+!12 = !{i32 990000, i64 166, i32 73}
+!13 = !{i32 999999, i64 3, i32 1443}
+!14 = !{!"function_entry_count", i64 100000}
+!15 = !{!"function_entry_count", i64 1}
+!16 = !{!"branch_weights", i32 1, i32 99999}
+!17 = !{!"section_prefix", !"hot"}
+!18 = !{!"section_prefix", !"unlikely"}
+
+;--- input-with-data-access-prof-off.ll
+; Same as file above except that module flag `EnableDataAccessProf` has value 0.
+; Internal vars
@hot_bss = internal global i32 0, !section_prefix !17
+ at data_unknown_hotness = internal global i32 1
+; External vars
+ at external_relro_array = constant [2 x ptr] [ptr @hot_bss, ptr @data_unknown_hotness], !section_prefix !18
+
+define void @cold_func() !prof !15 {
+ %9 = load i32, ptr @data_unknown_hotness
+ %11 = call i32 (...) @func_taking_arbitrary_param(i32 %9)
+ ret void
+}
define void @hot_func() !prof !14 {
%9 = load i32, ptr @hot_bss
@@ -21,8 +105,9 @@ define void @hot_func() !prof !14 {
declare i32 @func_taking_arbitrary_param(...)
-!llvm.module.flags = !{!1}
+!llvm.module.flags = !{!0, !1}
+!0 = !{i32 2, !"EnableDataAccessProf", i32 0}
!1 = !{i32 1, !"ProfileSummary", !2}
!2 = !{!3, !4, !5, !6, !7, !8, !9, !10}
!3 = !{!"ProfileFormat", !"InstrProf"}
@@ -40,3 +125,4 @@ declare i32 @func_taking_arbitrary_param(...)
!15 = !{!"function_entry_count", i64 1}
!16 = !{!"branch_weights", i32 1, i32 99999}
!17 = !{!"section_prefix", !"hot"}
+!18 = !{!"section_prefix", !"unlikely"}
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