[llvm] [SampleProfileMatcher] Fix inconsistent anchor matching in stale profile matching (PR #206657)

Mon Jun 29 23:51:14 PDT 2026

https://github.com/HighW4y2H3ll created https://github.com/llvm/llvm-project/pull/206657

Stale profile matching updates matched anchors inconsistently during the LCS matching -- when multiple profile is matched to one IR function during one LCS matching run, `FuncToProfileNameMap` will be overwritten with the last match, while `MatchedAnchors` only keeps the very first match (using `try_emplace`). This creates mismatched IR function to  Profile function mapping in `FuncToProfileNameMap` and `MatchedAnchors`.

This patch unifies the behavior by mirroring the use of `try_emplace` to update `FuncToProfileNameMap`.

>From c1c1d8414120661e67a1f99d12fca9898e0649c5 Mon Sep 17 00:00:00 2001
From: h2h <h2h at meta.com>
Date: Mon, 29 Jun 2026 23:37:06 -0700
Subject: [PATCH] Fix inconsistent anchor matching in stale profile matching

---
 .../Transforms/IPO/SampleProfileMatcher.cpp   |   2 +-
 .../stale-profile-lcs-anchor-overwrite.prof   |   7 ++
 .../stale-profile-lcs-anchor-overwrite.ll     | 118 ++++++++++++++++++
 3 files changed, 126 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/SampleProfile/Inputs/stale-profile-lcs-anchor-overwrite.prof
 create mode 100644 llvm/test/Transforms/SampleProfile/stale-profile-lcs-anchor-overwrite.ll

diff --git a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
index 6621684232812..79ffc333d530c 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
@@ -1036,7 +1036,7 @@ bool SampleProfileMatcher::functionMatchesProfile(Function &IRFunc,
   bool Matched = functionMatchesProfileHelper(IRFunc, ProfFunc);
   FuncProfileMatchCache[{&IRFunc, ProfFunc}] = Matched;
   if (Matched) {
-    FuncToProfileNameMap[&IRFunc] = ProfFunc;
+    FuncToProfileNameMap.try_emplace(&IRFunc, ProfFunc);
     LLVM_DEBUG(dbgs() << "Function:" << IRFunc.getName()
                       << " matches profile:" << ProfFunc << "\n");
   }
diff --git a/llvm/test/Transforms/SampleProfile/Inputs/stale-profile-lcs-anchor-overwrite.prof b/llvm/test/Transforms/SampleProfile/Inputs/stale-profile-lcs-anchor-overwrite.prof
new file mode 100644
index 0000000000000..5f9bc7be80d51
--- /dev/null
+++ b/llvm/test/Transforms/SampleProfile/Inputs/stale-profile-lcs-anchor-overwrite.prof
@@ -0,0 +1,7 @@
+_Z3fooi:29916:31
+ 349: 2 A:1 B:1
+ 350: 1 C:1
+ 6: _Z3bari:1843
+ 380: _Z3barl:323
+  3: _Z6calleei:306
+ !CFGChecksum: 1
diff --git a/llvm/test/Transforms/SampleProfile/stale-profile-lcs-anchor-overwrite.ll b/llvm/test/Transforms/SampleProfile/stale-profile-lcs-anchor-overwrite.ll
new file mode 100644
index 0000000000000..e01447c29e3de
--- /dev/null
+++ b/llvm/test/Transforms/SampleProfile/stale-profile-lcs-anchor-overwrite.ll
@@ -0,0 +1,118 @@
+; REQUIRES: x86_64-linux
+; REQUIRES: asserts
+; RUN: llvm-profdata merge --sample --extbinary %S/Inputs/stale-profile-lcs-anchor-overwrite.prof -o %t.prof
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%t.prof --salvage-stale-profile --salvage-unused-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl 2>&1 | FileCheck %s
+
+; CHECK: Function:_Z3barv matches profile:_Z3bari
+; CHECK: The functions _Z3barv(IR) and _Z3barl(Profile) share the same base name: bar.
+; CHECK: Function:_Z3barv matches profile:_Z3barl
+; CHECK: The functions _Z3barPv(IR) and _Z3barl(Profile) share the same base name: bar.
+; CHECK: Function:_Z3barPv matches profile:_Z3barl
+
+; CHECK: Run stale profile matching for _Z3barPv
+; CHECK: The functions _Z6calleePv(IR) and _Z6calleei(Profile) share the same base name: callee.
+; CHECK: Function:_Z6calleePv matches profile:_Z6calleei
+; CHECK: Location is matched from 1 to 1
+; CHECK: Callsite with callee:_Z6calleePv is matched from 2 to 3
+; CHECK: Run stale profile matching for _Z3barv
+; CHECK: Run stale profile matching for _Z6calleePv
+; CHECK: Function processing order:
+; CHECK: _Z3foov
+; CHECK: _Z3barPv
+; CHECK: _Z6calleePv
+; CHECK: _Z3barv
+
+
+target triple = "x86_64-linux-gnu"
+
+define dso_local noundef ptr @_Z6calleePv(ptr noundef %ptr) #0 !dbg !15 {
+entry:
+  %ptr.addr = alloca ptr, align 8
+  store ptr %ptr, ptr %ptr.addr, align 8
+    #dbg_declare(ptr %ptr.addr, !20, !DIExpression(), !21)
+  call void @llvm.pseudoprobe(i64 7108221232740920931, i64 1, i32 0, i64 -1), !dbg !22
+  ret ptr null, !dbg !22
+}
+
+define dso_local void @_Z3barv() #0 !dbg !23 {
+entry:
+  call void @llvm.pseudoprobe(i64 -1069303473483922844, i64 1, i32 0, i64 -1), !dbg !24
+  ret void, !dbg !24
+}
+
+define dso_local noundef ptr @_Z3barPv(ptr noundef %ptr) #0 !dbg !25 {
+entry:
+  %ptr.addr = alloca ptr, align 8
+  store ptr %ptr, ptr %ptr.addr, align 8
+    #dbg_declare(ptr %ptr.addr, !26, !DIExpression(), !27)
+  call void @llvm.pseudoprobe(i64 5678655469166311522, i64 1, i32 0, i64 -1), !dbg !28
+  %call = call noundef ptr @_Z6calleePv(ptr noundef null), !dbg !29
+  ret ptr %call, !dbg !31
+}
+
+define dso_local noundef ptr @_Z3foov() #0 !dbg !32 {
+entry:
+  call void @llvm.pseudoprobe(i64 9191153033785521275, i64 1, i32 0, i64 -1), !dbg !35
+  call void null(), !dbg !36
+  call void @_Z3barv(), !dbg !38
+  call void null(), !dbg !40
+  %call = call noundef ptr @_Z3barPv(ptr noundef null), !dbg !42
+  ret ptr %call, !dbg !44
+}
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite)
+declare void @llvm.pseudoprobe(i64, i64, i32, i64) #1
+
+attributes #0 = { "use-sample-profile" }
+attributes #1 = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!6, !7, !8, !9}
+!llvm.ident = !{!10}
+!llvm.pseudo_probe_desc = !{!11, !12, !13, !14}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2, splitDebugInlining: false, debugInfoForProfiling: true, nameTableKind: None)
+!1 = !DIFile(filename: "test.cc", directory: "/tmp", checksumkind: CSK_MD5, checksum: "e16862f6a655f30cd332532a91f867b6")
+!2 = !{!3}
+!3 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !4, size: 64)
+!4 = !DISubroutineType(types: !5)
+!5 = !{null}
+!6 = !{i32 7, !"Dwarf Version", i32 5}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 7, !"uwtable", i32 2}
+!9 = !{i32 7, !"frame-pointer", i32 2}
+!10 = !{!"clang"}
+!11 = !{i64 7108221232740920931, i64 4294967295, !"_Z6calleePv"}
+!12 = !{i64 -1069303473483922844, i64 4294967295, !"_Z3barv"}
+!13 = !{i64 5678655469166311522, i64 281479271677951, !"_Z3barPv"}
+!14 = !{i64 9191153033785521275, i64 1125904201809919, !"_Z3foov"}
+!15 = distinct !DISubprogram(name: "callee", linkageName: "_Z6calleePv", scope: !1, file: !1, line: 1, type: !16, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !19)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!18, !18}
+!18 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!19 = !{}
+!20 = !DILocalVariable(name: "ptr", arg: 1, scope: !15, file: !1, line: 1, type: !18)
+!21 = !DILocation(line: 1, column: 20, scope: !15)
+!22 = !DILocation(line: 2, column: 5, scope: !15)
+!23 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !4, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!24 = !DILocation(line: 5, column: 13, scope: !23)
+!25 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barPv", scope: !1, file: !1, line: 7, type: !16, scopeLine: 7, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !19)
+!26 = !DILocalVariable(name: "ptr", arg: 1, scope: !25, file: !1, line: 7, type: !18)
+!27 = !DILocation(line: 7, column: 17, scope: !25)
+!28 = !DILocation(line: 8, column: 12, scope: !25)
+!29 = !DILocation(line: 8, column: 12, scope: !30)
+!30 = !DILexicalBlockFile(scope: !25, file: !1, discriminator: 455082007)
+!31 = !DILocation(line: 8, column: 5, scope: !25)
+!32 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !1, file: !1, line: 11, type: !33, scopeLine: 11, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!33 = !DISubroutineType(types: !34)
+!34 = !{!18}
+!35 = !DILocation(line: 12, column: 5, scope: !32)
+!36 = !DILocation(line: 12, column: 5, scope: !37)
+!37 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 387973143)
+!38 = !DILocation(line: 13, column: 5, scope: !39)
+!39 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 455082015)
+!40 = !DILocation(line: 14, column: 5, scope: !41)
+!41 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 387973159)
+!42 = !DILocation(line: 15, column: 12, scope: !43)
+!43 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 455082031)
+!44 = !DILocation(line: 15, column: 5, scope: !32)

