[SHT_LLVM_BB_ADDR_MAP] Add assertion and clarify docstring

[boomanaiden154]

This patch adds an assertion to readBBAddrMapImpl to confirm that PGOAnalyses and BBAddrMaps are of the same size when PGO information is requested (part of the API contract). This patch also updates the docstring for readBBAddrMap to better clarify what is guaranteed.

[llvmbot]

@llvm/pr-subscribers-llvm-binary-utilities

Author: Aiden Grossman (boomanaiden154)

Changes

This patch adds an assertion to readBBAddrMapImpl to confirm that PGOAnalyses and BBAddrMaps are of the same size when PGO information is requested (part of the API contract). This patch also updates the docstring for readBBAddrMap to better clarify what is guaranteed.

---

Full diff: https://github.com/llvm/llvm-project/pull/77374.diff

2 Files Affected:

• (modified) llvm/include/llvm/Object/ELFObjectFile.h (+6-5)
• (modified) llvm/lib/Object/ELFObjectFile.cpp (+4)

diff --git a/llvm/include/llvm/Object/ELFObjectFile.h b/llvm/include/llvm/Object/ELFObjectFile.h
index 86f42654f8af8d..5182c6cf62c2c5 100644
--- a/llvm/include/llvm/Object/ELFObjectFile.h
+++ b/llvm/include/llvm/Object/ELFObjectFile.h
@@ -110,11 +110,12 @@ class ELFObjectFileBase : public ObjectFile {
   Expected<std::vector<VersionEntry>> readDynsymVersions() const;
 
   /// Returns a vector of all BB address maps in the object file. When
-  // `TextSectionIndex` is specified, only returns the BB address maps
-  // corresponding to the section with that index. When `PGOAnalyses`is
-  // specified, the vector is cleared then filled with extra PGO data.
-  // `PGOAnalyses` will always be the same length as the return value on
-  // success, otherwise it is empty.
+  /// `TextSectionIndex` is specified, only returns the BB address maps
+  /// corresponding to the section with that index. When `PGOAnalyses`is
+  /// specified, the vector is cleared then filled with extra PGO data.
+  /// When PGO information is requested (`PGOAnalyses` is not nullptr),
+  /// `PGOAnalyses` will always be the same length as the return value,
+  /// assuming no error occurs. Upon failure, `PGOAnalyses` will be empty.
   Expected<std::vector<BBAddrMap>>
   readBBAddrMap(std::optional<unsigned> TextSectionIndex = std::nullopt,
                 std::vector<PGOAnalysisMap> *PGOAnalyses = nullptr) const;
diff --git a/llvm/lib/Object/ELFObjectFile.cpp b/llvm/lib/Object/ELFObjectFile.cpp
index 95c4f9f8545db2..f43fdf8be58541 100644
--- a/llvm/lib/Object/ELFObjectFile.cpp
+++ b/llvm/lib/Object/ELFObjectFile.cpp
@@ -830,6 +830,10 @@ Expected<std::vector<BBAddrMap>> static readBBAddrMapImpl(
     std::move(BBAddrMapOrErr->begin(), BBAddrMapOrErr->end(),
               std::back_inserter(BBAddrMaps));
   }
+  if (PGOAnalyses)
+    assert(PGOAnalyses->size() == BBAddrMaps.size() &&
+           "The same number of BBAddrMaps and PGOAnalysisMaps should be "
+           "returned when PGO information is requested");
   return BBAddrMaps;
 }
 

[boomanaiden154]

Bump on this patch when reviewers have a chance. Thanks!

[rlavaee]

LGTM with a minor nit.

[red1bluelost]

LGTM with one nit about the comment

[red1bluelost]

LGTM