[llvm] [StaticDataLayout][MemProf] Record whether the IR is compiled with data access profiles by module flag. (PR #162333)

Tue Oct 7 10:49:53 PDT 2025

llvmbot wrote:




@llvm/pr-subscribers-pgo

Author: Mingming Liu (mingmingl-llvm)

<details>
<summary>Changes</summary>

The codegen pass in the pipeline can read the module flag to tell whether the IR is compiled with data access profile, to support two use cases when `memprof-annotate-static-data-prefix=true` is enabled

1. The binary is compiled with data access profiles. 
   - The module flag will have value 1, and codegen pass should regard an empty section prefix as 'unknown' and conservatively not placing the data into `.unlikely` data sections.

2. The binary is compiled without data access profiles (e.g., during incremental rollout, etc)
   - The module flag will have value 0, and codegen pass can override an empty section prefix based on PGO counters.

https://github.com/llvm/llvm-project/pull/155337  shows the motivating use case in function `StaticDataProfileInfo::getConstantSectionPrefix` in `llvm/lib/Analysis/StaticDataProfileInfo.cpp` 

---
Full diff: https://github.com/llvm/llvm-project/pull/162333.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Instrumentation/MemProfUse.cpp (+2) 
- (modified) llvm/test/Transforms/PGOProfile/data-access-profile.ll (+46-18) 


``````````diff

diff --git a/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp b/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
index c86092bd51eda..d86fcf268ce4f 100644
--- a/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemProfUse.cpp
@@ -798,6 +798,7 @@ bool MemProfUsePass::annotateGlobalVariables(
     return false;
 
   if (!DataAccessProf) {
+    M.addModuleFlag(Module::Warning, "EnableDataAccessProf", 0U);
     M.getContext().diagnose(DiagnosticInfoPGOProfile(
         MemoryProfileFileName.data(),
         StringRef("Data access profiles not found in memprof. Ignore "
@@ -805,6 +806,7 @@ bool MemProfUsePass::annotateGlobalVariables(
         DS_Warning));
     return false;
   }
+  M.addModuleFlag(Module::Warning, "EnableDataAccessProf", 1U);
 
   bool Changed = false;
   // Iterate all global variables in the module and annotate them based on
diff --git a/llvm/test/Transforms/PGOProfile/data-access-profile.ll b/llvm/test/Transforms/PGOProfile/data-access-profile.ll
index 29198f34ccbba..d9976a9d23755 100644
--- a/llvm/test/Transforms/PGOProfile/data-access-profile.ll
+++ b/llvm/test/Transforms/PGOProfile/data-access-profile.ll
@@ -3,22 +3,28 @@
 
 ; RUN: rm -rf %t && split-file %s %t && cd %t
 
-;; Read a text profile and merge it into indexed profile.
+;; Read text profiles and merge them into indexed profiles.
 ; RUN: llvm-profdata merge --memprof-version=4 memprof.yaml -o memprof.profdata
+; RUN: llvm-profdata merge --memprof-version=4 memprof-no-dap.yaml -o memprof-no-dap.profdata
 
 ;; Run optimizer pass on an IR module without IR functions, and test that global
 ;; variables in the module could be annotated (i.e., no early return),
 ; RUN: opt -passes='memprof-use<profile-filename=memprof.profdata>' -memprof-annotate-static-data-prefix \
-; RUN: -debug-only=memprof -stats -S funcless-module.ll -o - 2>&1 | FileCheck %s --check-prefixes=LOG,PREFIX,STAT
+; RUN: -debug-only=memprof -stats -S funcless-module.ll -o - 2>&1 | FileCheck %s --check-prefixes=LOG,IR,STAT
 
 ;; Run optimizer pass on the IR, and check the section prefix.
 ; RUN: opt -passes='memprof-use<profile-filename=memprof.profdata>' -memprof-annotate-static-data-prefix \
-; RUN: -debug-only=memprof -stats -S input.ll -o - 2>&1 | FileCheck %s --check-prefixes=LOG,PREFIX,STAT
+; RUN: -debug-only=memprof -stats -S input.ll -o - 2>&1 | FileCheck %s --check-prefixes=LOG,IR,STAT
 
-;; Run optimizer pass without explicitly setting -memprof-annotate-static-data-prefix.
-;; The output text IR shouldn't have `section_prefix`
+;; Run memprof without providing memprof data. Test that IR has module flag
+;; `EnableDataAccessProf` as 0.
+; RUN: opt -passes='memprof-use<profile-filename=memprof-no-dap.profdata>' -memprof-annotate-static-data-prefix \
+; RUN: -debug-only=memprof -stats -S input.ll -o - 2>&1 | FileCheck %s --check-prefix=FLAG
+
+;; Run memprof without explicitly setting -memprof-annotate-static-data-prefix.
+;; The output text IR shouldn't have `section_prefix` or EnableDataAccessProf module flag.
 ; RUN: opt -passes='memprof-use<profile-filename=memprof.profdata>' \
-; RUN: -debug-only=memprof -stats -S input.ll -o - | FileCheck %s --implicit-check-not="section_prefix"
+; RUN: -debug-only=memprof -stats -S input.ll -o - | FileCheck %s --check-prefix=FLAGLESS --implicit-check-not="section_prefix"
 
 ; LOG: Skip annotating string literal .str
 ; LOG: Global variable var1 is annotated as hot
@@ -29,29 +35,33 @@
 ; LOG: Global variable var4 has explicit section name. Skip annotating.
 
 ;; String literals are not annotated.
-; PREFIX: @.str = unnamed_addr constant [5 x i8] c"abcde"
-; PREFIX-NOT: section_prefix
-; PREFIX: @var1 = global i32 123, !section_prefix !0
+; IR: @.str = unnamed_addr constant [5 x i8] c"abcde"
+; IR-NOT: section_prefix
+; IR: @var1 = global i32 123, !section_prefix !0
 
 ;; @var.llvm.125 will be canonicalized to @var2 for profile look-up.
-; PREFIX-NEXT: @var2.llvm.125 = global i64 0, !section_prefix !0
+; IR-NEXT: @var2.llvm.125 = global i64 0, !section_prefix !0
 
 ;; @bar is not seen in hot symbol or known symbol set, so it won't get a section
 ;; prefix. Test this by testing that there is no section_prefix between @bar and
 ;; @foo.
-; PREFIX-NEXT: @bar = global i16 3
-; PREFIX-NOT: !section_prefix
+; IR-NEXT: @bar = global i16 3
+; IR-NOT: !section_prefix
 
 ;; @foo is unlikely.
-; PREFIX-NEXT: @foo = global i8 2, !section_prefix !1
+; IR-NEXT: @foo = global i8 2, !section_prefix !1
+
+; IR-NEXT: @var3 = constant [2 x i32] [i32 12345, i32 6789], section "sec1"
+; IR-NEXT: @var4 = constant [1 x i64] [i64 98765] #0
 
-; PREFIX-NEXT: @var3 = constant [2 x i32] [i32 12345, i32 6789], section "sec1"
-; PREFIX-NEXT: @var4 = constant [1 x i64] [i64 98765] #0
+; IR: attributes #0 = { "rodata-section"="sec2" }
 
-; PREFIX: attributes #0 = { "rodata-section"="sec2" }
+; IR: !0 = !{!"section_prefix", !"hot"}
+; IR-NEXT: !1 = !{!"section_prefix", !"unlikely"}
+; IR-NEXT: !2 = !{i32 2, !"EnableDataAccessProf", i32 1}
 
-; PREFIX: !0 = !{!"section_prefix", !"hot"}
-; PREFIX-NEXT: !1 = !{!"section_prefix", !"unlikely"}
+; FLAG: !{i32 2, !"EnableDataAccessProf", i32 0}
+; FLAGLESS-NOT: EnableDataAccessProf
 
 ; STAT: 1 memprof - Number of global vars annotated with 'unlikely' section prefix.
 ; STAT: 2 memprof - Number of global vars with user-specified section (not annotated).
@@ -72,6 +82,24 @@ DataAccessProfiles:
     - foo
   KnownColdStrHashes: [ 999, 1001 ]
 ...
+;--- memprof-no-dap.yaml
+---
+# A memprof file with without data access profiles. The heap records are simplified
+# to pass profile parsing and don't need to match the IR.
+HeapProfileRecords:
+  - GUID:            0xdeadbeef12345678
+    AllocSites:
+      - Callstack:
+          - { Function: 0x1111111111111111, LineOffset: 11, Column: 10, IsInlineFrame: true }
+        MemInfoBlock:
+          AllocCount:      111
+          TotalSize:       222
+          TotalLifetime:   333
+          TotalLifetimeAccessDensity: 444
+    CallSites:
+      - Frames:
+        - { Function: 0x5555555555555555, LineOffset: 55, Column: 50, IsInlineFrame: true }
+...
 ;--- input.ll
 
 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"

``````````

</details>


https://github.com/llvm/llvm-project/pull/162333
