[llvm] [SamplePGO] Handle FS discriminators in SampleProfileMatcher (PR #90858)

[Krzysztof Pszeniczny via llvm-commits]

https://github.com/amharc created https://github.com/llvm/llvm-project/pull/90858

Currently the code uses FunctionSamples::getCallSiteIdentifier which will sometimes incorrectly guess that FSAFDO discriminators are probe based and will convert them incorrectly.

This change doesn't affect builds which don't use FSAFDO, it only fixes sample profile matching with FS discriminators.

The test for this is manually updated to use discriminator value 15, which is a perfectly valid base discriminator in the FS world, but satisfies `isPseudoProbeDiscriminator`, so
`getBaseDiscriminatorFromDiscriminator` will incorrectly extract the probe index from it.

Note: this change only affects how the base discriminators will be extracted when doing stale profile matching in the IR-level sample profile loader. It doesn't add stale profile matching to the MIR-level FS profile loader pass.

>From 7ade1c9682ba896fe829dfa8bd5d7a85748e267c Mon Sep 17 00:00:00 2001
From: Krzysztof Pszeniczny <kpszeniczny at google.com>
Date: Thu, 25 Apr 2024 11:41:28 +0200
Subject: [PATCH] [SamplePGO] Handle FS discriminators in SampleProfileMatcher

Currently the code uses FunctionSamples::getCallSiteIdentifier which
will sometimes incorrectly guess that FSAFDO discriminators are probe
based and will convert them incorrectly.

This change doesn't affect builds which don't use FSAFDO, it only fixes
sample profile matching with FS discriminators.

The test for this is manually updated to use discriminator value 15,
which is a perfectly valid base discriminator in the FS world, but
satisfies `isPseudoProbeDiscriminator`, so
`getBaseDiscriminatorFromDiscriminator` will incorrectly extract the
probe index from it.

Note: this change only affects how the base discriminators will be
extracted when doing stale profile matching in the IR-level sample
profile loader. It doesn't add stale profile matching to the MIR-level
FS profile loader pass.
---
 llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp          | 6 ++++--
 .../Inputs/non-probe-stale-profile-matching.prof          | 4 ++--
 .../SampleProfile/non-probe-stale-profile-matching.ll     | 8 ++++----
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
index 1ca89e0091daff..142660bcc58e34 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
@@ -37,7 +37,8 @@ void SampleProfileMatcher::findIRAnchors(
       DIL = DIL->getInlinedAt();
     } while (DIL->getInlinedAt());
 
-    LineLocation Callsite = FunctionSamples::getCallSiteIdentifier(DIL);
+    LineLocation Callsite = FunctionSamples::getCallSiteIdentifier(
+        DIL, FunctionSamples::ProfileIsFS);
     StringRef CalleeName = PrevDIL->getSubprogramLinkageName();
     return std::make_pair(Callsite, CalleeName);
   };
@@ -82,7 +83,8 @@ void SampleProfileMatcher::findIRAnchors(
         if (DIL->getInlinedAt()) {
           IRAnchors.emplace(FindTopLevelInlinedCallsite(DIL));
         } else {
-          LineLocation Callsite = FunctionSamples::getCallSiteIdentifier(DIL);
+          LineLocation Callsite = FunctionSamples::getCallSiteIdentifier(
+              DIL, FunctionSamples::ProfileIsFS);
           StringRef CalleeName = GetCanonicalCalleeName(dyn_cast<CallBase>(&I));
           IRAnchors.emplace(Callsite, CalleeName);
         }
diff --git a/llvm/test/Transforms/SampleProfile/Inputs/non-probe-stale-profile-matching.prof b/llvm/test/Transforms/SampleProfile/Inputs/non-probe-stale-profile-matching.prof
index 8e988515be8ed5..418f2c4af26460 100644
--- a/llvm/test/Transforms/SampleProfile/Inputs/non-probe-stale-profile-matching.prof
+++ b/llvm/test/Transforms/SampleProfile/Inputs/non-probe-stale-profile-matching.prof
@@ -10,12 +10,12 @@ main:9229397:0
  7: 0
  2: foo:1479916
   1: 47663
-  1.1: 46683 bar:43238
+  1.15: 46683 bar:43238
   2: 4519 bar:4932
   3: 48723
  4: foo:1505537
   1: 48604
-  1.1: 46965 bar:44479
+  1.15: 46965 bar:44479
   2: 4613 bar:4967
   3: 49087
 bar:2333388:196222
diff --git a/llvm/test/Transforms/SampleProfile/non-probe-stale-profile-matching.ll b/llvm/test/Transforms/SampleProfile/non-probe-stale-profile-matching.ll
index eb69c18add01b8..5394a00ced86ad 100644
--- a/llvm/test/Transforms/SampleProfile/non-probe-stale-profile-matching.ll
+++ b/llvm/test/Transforms/SampleProfile/non-probe-stale-profile-matching.ll
@@ -1,6 +1,6 @@
 ; REQUIRES: x86_64-linux
 ; REQUIRES: asserts
-; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/non-probe-stale-profile-matching.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl 2>&1 | FileCheck %s
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/non-probe-stale-profile-matching.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl -profile-isfs 2>&1 | FileCheck %s
 
 ; The profiled source code:
 
@@ -51,7 +51,7 @@
 ; CHECK: Run stale profile matching for bar
 
 ; CHECK: Run stale profile matching for foo
-; CHECK: Callsite with callee:bar is matched from 1.1 to 1.1
+; CHECK: Callsite with callee:bar is matched from 1.15 to 1.15
 ; CHECK: Callsite with callee:bar is matched from 2 to 2
 
 ; CHECK: Run stale profile matching for main
@@ -183,7 +183,7 @@ attributes #3 = { mustprogress nocallback nofree nosync nounwind willreturn memo
 !15 = !DILocation(line: 7, column: 9, scope: !14)
 !16 = !DILocation(line: 7, column: 7, scope: !14)
 !17 = !DILocation(line: 7, column: 23, scope: !18)
-!18 = !DILexicalBlockFile(scope: !14, file: !10, discriminator: 2)
+!18 = !DILexicalBlockFile(scope: !14, file: !10, discriminator: 15)
 !19 = !DILocation(line: 7, column: 15, scope: !18)
 !20 = !DILocation(line: 8, column: 21, scope: !14)
 !21 = !DILocation(line: 8, column: 15, scope: !14)
@@ -201,7 +201,7 @@ attributes #3 = { mustprogress nocallback nofree nosync nounwind willreturn memo
 !33 = !DILocation(line: 14, column: 8, scope: !25)
 !34 = !DILocation(line: 14, scope: !25)
 !35 = !DILocation(line: 14, column: 21, scope: !36)
-!36 = !DILexicalBlockFile(scope: !25, file: !10, discriminator: 2)
+!36 = !DILexicalBlockFile(scope: !25, file: !10, discriminator: 15)
 !37 = !DILocation(line: 14, column: 3, scope: !36)
 !38 = !DILocation(line: 14, column: 3, scope: !39)
 !39 = !DILexicalBlockFile(scope: !25, file: !10, discriminator: 4)