Always check the function attribute to determine checksum mismatch for available_externally functions

[wlei-llvm]

This is to fix an assertion error. Apparently, pseudo_probe_desc could still be available for import functions, and its checksum mismatch state can be different from import function's profile-checksum-mismatch attr. This happens when unstable IR or ODR violation issue occurs, the definitions of the same function across different translation units could be different and result in different checksums. During link time deduplication, the internal function definition (the checksum in desc is computed based on) is substituted by the available_externally definition, which cause the inconsistency. Hence, we fix it to by always checking the state for the new available_externally definition, which is saved in the function attribute.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Lei Wang (wlei-llvm)

Changes

pseudo_probe_desc could still be available for import functions, this happens when an internal function(the desc is computed based on) is substituted by the available_externally function, e.g. the template function, their mismatch state could be different and we should use state from the new one. Hence, changed it to always check the function attribute to determine checksum mismatch for available_externally functions.

---

Full diff: https://github.com/llvm/llvm-project/pull/87279.diff

2 Files Affected:

• (modified) llvm/include/llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h (+16-7)
• (modified) llvm/test/Transforms/SampleProfile/pseudo-probe-callee-profile-mismatch.ll (+6-3)

diff --git a/llvm/include/llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h b/llvm/include/llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h
index d898ee58307ead..3098bba115c328 100644
--- a/llvm/include/llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h
+++ b/llvm/include/llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h
@@ -129,16 +129,25 @@ class PseudoProbeManager {
 
   bool profileIsValid(const Function &F, const FunctionSamples &Samples) const {
     const auto *Desc = getDesc(F);
-    assert((LTOPhase != ThinOrFullLTOPhase::ThinLTOPostLink || !Desc ||
+    bool IsAvailableExternallyLinkage =
+        GlobalValue::isAvailableExternallyLinkage(F.getLinkage());
+    // Always check the function attribute to determine checksum mismatch for
+    // `available_externally` functions even their desc is available. This is
+    // because the desc is computed based on the original internal function
+    // which is substituted by the `available_externally` function, their
+    // mismatch state could be different and we should use state from the new
+    // one.
+    assert((LTOPhase != ThinOrFullLTOPhase::ThinLTOPostLink ||
+            IsAvailableExternallyLinkage || !Desc ||
             profileIsHashMismatched(*Desc, Samples) ==
                 F.hasFnAttribute("profile-checksum-mismatch")) &&
-           "In post-link, profile checksum matching state doesn't match "
-           "function 'profile-checksum-mismatch' attribute.");
+           "In post-link, profile checksum matching state doesn't match the "
+           "internal function's 'profile-checksum-mismatch' attribute.");
     (void)LTOPhase;
-    // The desc for import function is unavailable. Check the function attribute
-    // for mismatch.
-    return (!Desc && !F.hasFnAttribute("profile-checksum-mismatch")) ||
-           (Desc && !profileIsHashMismatched(*Desc, Samples));
+    if (IsAvailableExternallyLinkage || !Desc)
+      return !F.hasFnAttribute("profile-checksum-mismatch");
+
+    return Desc && !profileIsHashMismatched(*Desc, Samples);
   }
 };
 
diff --git a/llvm/test/Transforms/SampleProfile/pseudo-probe-callee-profile-mismatch.ll b/llvm/test/Transforms/SampleProfile/pseudo-probe-callee-profile-mismatch.ll
index 4881937df101ac..43be142e7cf98f 100644
--- a/llvm/test/Transforms/SampleProfile/pseudo-probe-callee-profile-mismatch.ll
+++ b/llvm/test/Transforms/SampleProfile/pseudo-probe-callee-profile-mismatch.ll
@@ -1,7 +1,9 @@
 ; REQUIRES: x86_64-linux
 ; REQUIRES: asserts
-; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-callee-profile-mismatch.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl  -pass-remarks=inline 2>&1 | FileCheck %s
+; RUN: opt < %s -passes='thinlto<O2>' -pgo-kind=pgo-sample-use-pipeline  -sample-profile-file=%S/Inputs/pseudo-probe-callee-profile-mismatch.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl  -pass-remarks=inline 2>&1 | FileCheck %s
 
+; There is no profile-checksum-mismatch attr, even the checksum is mismatched in the pseudo_probe_desc, it doesn't run the matching.
+; CHECK-NOT: Run stale profile matching for main
 
 ; CHECK: Run stale profile matching for bar
 ; CHECK: Callsite with callee:baz is matched from 4 to 2
@@ -14,7 +16,7 @@
 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"
 
-define i32 @main() #0 {
+define available_externally i32 @main() #0 {
   %1 = call i32 @bar(), !dbg !13
   ret i32 0
 }
@@ -47,7 +49,8 @@ attributes #1 = { "profile-checksum-mismatch" "use-sample-profile" }
 !9 = distinct !DICompileUnit(language: DW_LANG_C11, file: !10, producer: "clang version 19.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
 !10 = !DIFile(filename: "test2.c", directory: "/home/test", checksumkind: CSK_MD5, checksum: "553093afc026f9c73562eb3b0c5b7532")
 !11 = !{i32 2, !"Debug Info Version", i32 3}
-!12 = !{i64 -2624081020897602054, i64 281582081721716, !"main"}
+; Make a checksum mismatch in the pseudo_probe_desc
+!12 = !{i64 -2624081020897602054, i64 123456, !"main"}
 !13 = !DILocation(line: 8, column: 10, scope: !14)
 !14 = !DILexicalBlockFile(scope: !15, file: !1, discriminator: 186646591)
 !15 = distinct !DILexicalBlock(scope: !16, file: !1, line: 7, column: 40)

[WenleiHe]

e.g. the template function, their mismatch state could be different and we should use state from the new one.

Worth calling out why this happens and whether this is actually expected.

[WenleiHe]

LGTM with nit, thanks.