[PATCH] D123872: Force GHashCell to be 8-byte-aligned.

[Eli Friedman via Phabricator via llvm-commits]

efriedma created this revision.
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Otherwise, with recent versions of libstdc++, clang can't tell that the atomic operations are properly aligned, and generates calls to libatomic.

Fixes https://github.com/llvm/llvm-project/issues/54790 , at least for that specific case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123872

Files:
  lld/COFF/DebugTypes.cpp


Index: lld/COFF/DebugTypes.cpp
===================================================================
--- lld/COFF/DebugTypes.cpp
+++ lld/COFF/DebugTypes.cpp
@@ -902,7 +902,11 @@
 
 /// A ghash table cell for deduplicating types from TpiSources.
 class GHashCell {
-  uint64_t data = 0;
+  // Force "data" to be 64-bit aligned; otherwise, some versions of clang
+  // will generate calls to libatomic when using some versions of libstdc++
+  // on 32-bit targets.  (Also, in theory, there could be a target where
+  // new[] doesn't always return an 8-byte-aligned allocation.)
+  alignas(sizeof(uint64_t)) uint64_t data = 0;
 
 public:
   GHashCell() = default;


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