[NFC][StaticDataProfileInfo] Refactor StaticDataProfileInfo::getConstantSectionPrefix and extract analysis based on PGO-counter to be a helper function #162388

mingmingl-llvm · 2025-10-07T22:26:52Z

StaticDataProfileInfo::getConstantSectionPrefix is used twice in codegen ([1] and [2]) to emit section prefix for constants.

Before this patch, its implementation does analysis using PGO-counters, and PGO-counters are only available on module-internal constants.

After this patch, the PGO-counter analysis are extracted to a helper function, and returns enum rather than StringPrefix. This way, the follow up patch #163325 can extend this function to use global variable section prefix and compute a max (the hotter one).

[1]

llvm-project/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

Lines 3014 to 3019 in 975fba1

    
           StringRef AsmPrinter::getConstantSectionSuffix(const Constant *C) const { 
        
             if (TM.Options.EnableStaticDataPartitioning && C && SDPI && PSI) 
        
               return SDPI->getConstantSectionPrefix(C, PSI); 
        
             return ""; 
        
           }

[2]

llvm-project/llvm/lib/CodeGen/StaticDataAnnotator.cpp

Lines 77 to 84 in 975fba1

    
           for (auto &GV : M.globals()) { 
        
             if (!llvm::memprof::IsAnnotationOK(GV)) 
        
               continue; 
        
             StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI); 
        
             // setSectionPrefix returns true if the section prefix is updated. 
        
             Changed |= GV.setSectionPrefix(SectionPrefix); 
        
           }

llvmbot · 2025-10-14T19:01:06Z

@llvm/pr-subscribers-llvm-analysis

Author: Mingming Liu (mingmingl-llvm)

Changes

StaticDataProfileInfo::getConstantSectionPrefix is used twice in codegen ([1] and [2]) to emit section prefix for constants.

Before this patch, its implementation does analysis using PGO-counters, and PGO-counters are only available on module-internal constants.

After this patch, the PGO-counter analysis are extracted to a helper function, and returns enum rather than StringPrefix. This way, the follow up patch #163325 can extend this function to use global variable section prefix and compute a max (the hotter one).

[1]

llvm-project/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

Lines 3014 to 3019 in 975fba1

    
           StringRef AsmPrinter::getConstantSectionSuffix(const Constant *C) const { 
        
             if (TM.Options.EnableStaticDataPartitioning && C && SDPI && PSI) 
        
               return SDPI->getConstantSectionPrefix(C, PSI); 
        
             return ""; 
        
           }

[2]

llvm-project/llvm/lib/CodeGen/StaticDataAnnotator.cpp

Lines 77 to 84 in 975fba1

    
           for (auto &GV : M.globals()) { 
        
             if (!llvm::memprof::IsAnnotationOK(GV)) 
        
               continue; 
        
             StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI); 
        
             // setSectionPrefix returns true if the section prefix is updated. 
        
             Changed |= GV.setSectionPrefix(SectionPrefix); 
        
           }

Full diff: https://github.com/llvm/llvm-project/pull/162388.diff

2 Files Affected:

(modified) llvm/include/llvm/Analysis/StaticDataProfileInfo.h (+19-2)
(modified) llvm/lib/Analysis/StaticDataProfileInfo.cpp (+33-15)

diff --git a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
index f06e7ceaa74ce..70199a904f320 100644
--- a/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
+++ b/llvm/include/llvm/Analysis/StaticDataProfileInfo.h
@@ -32,8 +32,11 @@ bool IsAnnotationOK(const GlobalVariable &GV);
 /// profile information and provides methods to operate on them.
 class StaticDataProfileInfo {
 public:
-  /// Accummulate the profile count of a constant that will be lowered to static
-  /// data sections.
+  /// A constant is tracked only if the following conditions are met.
+  ///   1) It has local (i.e., private or internal) linkage.
+  //    2) Its data kind is one of {.rodata, .data, .bss, .data.rel.ro}.
+  //    3) It's eligible for section prefix annotation. See `AnnotationKind`
+  //       above for ineligible reasons.
   DenseMap<const Constant *, uint64_t> ConstantProfileCounts;
 
   /// Keeps track of the constants that are seen at least once without profile
@@ -44,6 +47,20 @@ class StaticDataProfileInfo {
   LLVM_ABI std::optional<uint64_t>
   getConstantProfileCount(const Constant *C) const;
 
+  enum class StaticDataHotness : uint8_t {
+    Cold = 0,
+    LukewarmOrUnknown = 1,
+    Hot = 2,
+  };
+
+  /// Return the hotness of the constant \p C based on its profile count \p
+  /// Count.
+  LLVM_ABI StaticDataHotness getSectionHotnessUsingProfileCount(
+      const Constant *C, const ProfileSummaryInfo *PSI, uint64_t Count) const;
+
+  /// Return the string representation of the hotness enum \p Hotness.
+  LLVM_ABI StringRef hotnessToStr(StaticDataHotness Hotness) const;
+
 public:
   StaticDataProfileInfo() = default;
 
diff --git a/llvm/lib/Analysis/StaticDataProfileInfo.cpp b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
index 1f751ee5e09d9..27f8d216454aa 100644
--- a/llvm/lib/Analysis/StaticDataProfileInfo.cpp
+++ b/llvm/lib/Analysis/StaticDataProfileInfo.cpp
@@ -60,6 +60,37 @@ void StaticDataProfileInfo::addConstantProfileCount(
     OriginalCount = getInstrMaxCountValue();
 }
 
+StaticDataProfileInfo::StaticDataHotness
+StaticDataProfileInfo::getSectionHotnessUsingProfileCount(
+    const Constant *C, const ProfileSummaryInfo *PSI, uint64_t Count) const {
+  // The accummulated counter shows the constant is hot. Return 'hot' whether
+  // this variable is seen by unprofiled functions or not.
+  if (PSI->isHotCount(Count))
+    return StaticDataHotness::Hot;
+  // The constant is not hot, and seen by unprofiled functions. We don't want to
+  // assign it to unlikely sections, even if the counter says 'cold'. So return
+  // an empty prefix before checking whether the counter is cold.
+  if (ConstantWithoutCounts.count(C))
+    return StaticDataHotness::LukewarmOrUnknown;
+  // The accummulated counter shows the constant is cold. Return 'unlikely'.
+  if (PSI->isColdCount(Count))
+    return StaticDataHotness::Cold;
+
+  return StaticDataHotness::LukewarmOrUnknown;
+}
+
+StringRef StaticDataProfileInfo::hotnessToStr(
+    StaticDataProfileInfo::StaticDataHotness Hotness) const {
+  switch (Hotness) {
+  case StaticDataProfileInfo::StaticDataHotness::Cold:
+    return "unlikely";
+  case StaticDataProfileInfo::StaticDataHotness::Hot:
+    return "hot";
+  default:
+    return "";
+  }
+}
+
 std::optional<uint64_t>
 StaticDataProfileInfo::getConstantProfileCount(const Constant *C) const {
   auto I = ConstantProfileCounts.find(C);
@@ -70,23 +101,10 @@ StaticDataProfileInfo::getConstantProfileCount(const Constant *C) const {
 
 StringRef StaticDataProfileInfo::getConstantSectionPrefix(
     const Constant *C, const ProfileSummaryInfo *PSI) const {
-  auto Count = getConstantProfileCount(C);
+  std::optional<uint64_t> Count = getConstantProfileCount(C);
   if (!Count)
     return "";
-  // The accummulated counter shows the constant is hot. Return 'hot' whether
-  // this variable is seen by unprofiled functions or not.
-  if (PSI->isHotCount(*Count))
-    return "hot";
-  // The constant is not hot, and seen by unprofiled functions. We don't want to
-  // assign it to unlikely sections, even if the counter says 'cold'. So return
-  // an empty prefix before checking whether the counter is cold.
-  if (ConstantWithoutCounts.count(C))
-    return "";
-  // The accummulated counter shows the constant is cold. Return 'unlikely'.
-  if (PSI->isColdCount(*Count))
-    return "unlikely";
-  // The counter says lukewarm. Return an empty prefix.
-  return "";
+  return hotnessToStr(getSectionHotnessUsingProfileCount(C, PSI, *Count));
 }
 
 bool StaticDataProfileInfoWrapperPass::doInitialization(Module &M) {

snehasish

lgtm with some minor nits.

snehasish · 2025-10-14T21:03:09Z

llvm/include/llvm/Analysis/StaticDataProfileInfo.h


+  enum class StaticDataHotness : uint8_t {
+    Cold = 0,
+    LukewarmOrUnknown = 1,


Prefer unknown as 0 so that any accidentally uninitialized value will default to unknown.

Meanwhile updated the enum class def to be signed enums.

snehasish · 2025-10-14T21:06:48Z

llvm/include/llvm/Analysis/StaticDataProfileInfo.h

+
+  /// Return the hotness of the constant \p C based on its profile count \p
+  /// Count.
+  LLVM_ABI StaticDataHotness getSectionHotnessUsingProfileCount(


Can we name this getConstantHotnessUsingProfileCount? I wasn't sure what is implied by the word section in the name.

snehasish · 2025-10-14T21:07:37Z

llvm/lib/Analysis/StaticDataProfileInfo.cpp

+    return StaticDataHotness::Hot;
+  // The constant is not hot, and seen by unprofiled functions. We don't want to
+  // assign it to unlikely sections, even if the counter says 'cold'. So return
+  // an empty prefix before checking whether the counter is cold.


nit: this returns an enum now, same for the comment below.

snehasish · 2025-10-14T21:09:31Z

llvm/lib/Analysis/StaticDataProfileInfo.cpp

+StringRef StaticDataProfileInfo::hotnessToStr(
+    StaticDataProfileInfo::StaticDataHotness Hotness) const {
+  switch (Hotness) {
+  case StaticDataProfileInfo::StaticDataHotness::Cold:


Is the StaticDataProfileInfo qualifier needed here?

Oh good catch! I removed the qualifier to make code simpler.

mingmingl-llvm · 2025-10-15T04:15:23Z

Error from both linux and windows are around clang/test/CodeGenHLSL/resources/StructuredBuffers-methods-lib.hlsl:29 and clang/test/CodeGenHLSL/resources/StructuredBuffers-methods-ps.hlsl:26, and are not related with this codegen change.

Will merge this change.

…ata 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 #162388

…nters 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 llvm/llvm-project#162388

Base automatically changed from users/mingmingl-llvm/setsectionprefix to main October 13, 2025 19:02

squash commits

3d70a00

mingmingl-llvm force-pushed the users/mingmingl-llvm/prepatch branch from 8c64a53 to 3d70a00 Compare October 13, 2025 23:44

Merge branch 'main' into users/mingmingl-llvm/prepatch

9a177c2

mingmingl-llvm changed the title ~~Refactor getConstantSectionPrefix to prepare for the next change~~ [NFC][StaticDataProfileInfo] Refactor StaticDataProfileInfo::getConstantSectionPrefix and extract analysis based on PGO-counter to be a helper function Oct 14, 2025

mingmingl-llvm requested review from snehasish and teresajohnson October 14, 2025 19:00

mingmingl-llvm marked this pull request as ready for review October 14, 2025 19:00

llvmbot added the llvm:analysis Includes value tracking, cost tables and constant folding label Oct 14, 2025

mingmingl-llvm mentioned this pull request Oct 14, 2025

[StaticDataLayout] Reconcile data hotness based on PGO counters and data access profiles #163325

Merged

snehasish approved these changes Oct 14, 2025

View reviewed changes

resolve comments

433f716

mingmingl-llvm merged commit c63002e into main Oct 15, 2025
8 of 10 checks passed

mingmingl-llvm deleted the users/mingmingl-llvm/prepatch branch October 15, 2025 04:15

mingmingl-llvm restored the users/mingmingl-llvm/prepatch branch October 15, 2025 04:29

mingmingl-llvm deleted the users/mingmingl-llvm/prepatch branch October 15, 2025 04:42

	StringRef AsmPrinter::getConstantSectionSuffix(const Constant *C) const {
	if (TM.Options.EnableStaticDataPartitioning && C && SDPI && PSI)
	return SDPI->getConstantSectionPrefix(C, PSI);

	return "";
	}

	for (auto &GV : M.globals()) {
	if (!llvm::memprof::IsAnnotationOK(GV))
	continue;

	StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI);
	// setSectionPrefix returns true if the section prefix is updated.
	Changed \|= GV.setSectionPrefix(SectionPrefix);
	}

[NFC][StaticDataProfileInfo] Refactor StaticDataProfileInfo::getConstantSectionPrefix and extract analysis based on PGO-counter to be a helper function #162388

[NFC][StaticDataProfileInfo] Refactor StaticDataProfileInfo::getConstantSectionPrefix and extract analysis based on PGO-counter to be a helper function #162388

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