[BOLT][YAML] Only read first profile per function

[Amir]

Summary

D159460 regressed the bugfix in D156644. Fix that and emit a warning.
Add a test case.

[maksfb]

bolt/lib/Profile/YAMLProfileReader.cpp

307

Unneeded.

[Amir]

bolt/lib/Profile/YAMLProfileReader.cpp

307

It is needed because the attaching happens in lines 341-354. Preliminary exec count assignment is a suitable place where it's easy/cheap to check if the profile was attached already.

[maksfb]

bolt/lib/Profile/YAMLProfileReader.cpp

307

Then you need auto &BF.

[Amir]

bolt/lib/Profile/YAMLProfileReader.cpp

307

As discussed offline, this structured binding expands into reference types so modifying BF here has an effect.

[Amir]

bolt/lib/Profile/YAMLProfileReader.cpp

307

Relevant note from Programmer's Manual:

Note that the elements are provided through a ‘reference wrapper’ proxy type (tuple of references), which combined with the structured bindings declaration makes Letter and Count references to range elements. Any modification to these references will affect the elements of Letters or Counts.

https://llvm.org/docs/ProgrammersManual.html#the-zip-functions

[maksfb]

bolt/lib/Profile/YAMLProfileReader.cpp

307

Cool.

bolt/lib/Profile/YAMLProfileReader.cpp

if (YamlBP.Header.EventNames.find(',') != StringRef::npos)
     return make_error<StringError>(
         Twine("multiple events in profile are not supported"),
         inconvertibleErrorCode());
 
   // Match profile to function based on a function name.
   buildNameMaps(BC);
 
   // Preliminary assign function execution count.
-  for (auto [YamlBF, BF] : llvm::zip_equal(YamlBP.Functions, ProfileBFs))
-    if (BF)
+  for (auto [YamlBF, BF] : llvm::zip_equal(YamlBP.Functions, ProfileBFs)) {
+    if (!BF)
+      continue;
+    if (!BF->hasProfile()) {
       BF->setExecutionCount(YamlBF.ExecCount);
+    } else {
+      if (opts::Verbosity >= 1) {
+        errs() << "BOLT-WARNING: dropping duplicate profile for " << YamlBF.Name
+               << '\n';
+      }
+      BF = nullptr;
+    }
+  }
 
   return Error::success();
 }
 
 bool YAMLProfileReader::mayHaveProfileData(const BinaryFunction &BF) {
   for (StringRef Name : BF.getNames())
     if (ProfileFunctionNames.contains(Name))
       return true;

bolt/test/X86/yaml-multiple-profiles.test

+# This test ensures that a YAML profile with multiple profiles matching the same
+# function is handled gracefully.
+
+# REQUIRES: system-linux
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %t/main.s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -nostdlib
+# RUN: llvm-bolt %t.exe -o /dev/null --data %t/profile.yaml \
+# RUN:   --profile-ignore-hash -v=1 2>&1 | FileCheck %s
+# CHECK: BOLT-WARNING: dropping duplicate profile for main_alias(*2)
+#--- main.s
+  .globl main_alias
+  .type main_alias, %function
+main_alias:
+  .globl main
+  .type main, %function
+main:
+  .cfi_startproc
+  cmpl  $0x0, %eax
+  retq
+  .cfi_endproc
+.size main, .-main
+.size main_alias, .-main_alias
+#--- profile.yaml
+---
+header:
+  profile-version: 1
+  binary-name:     'yaml-multiple-profiles.test.tmp.exe'
+  binary-build-id: '<unknown>'
+  profile-flags:   [ lbr ]
+  profile-origin:  branch profile reader
+  profile-events:  ''
+  dfs-order:       false
+functions:
+  - name:            'main(*2)'
+    fid:             1
+    hash:            0x50BBA3441D436491
+    exec:            1
+    nblocks:         1
+    blocks:
+      - bid:             0
+        insns:           2
+        hash:            0x4D4D8FAF7D4C0000
+  - name:            'main_alias(*2)'
+    fid:             1
+    hash:            0x50BBA3441D436491
+    exec:            1
+    nblocks:         1
+    blocks:
+      - bid:             0
+        insns:           2
+        hash:            0x4D4D8FAF7D4C0000
+...