[PATCH] D133361: [BPF] Attribute preserve_static_offset for structs

[Erich Keane via Phabricator via cfe-commits]

erichkeane added inline comments.


================
Comment at: clang/lib/CodeGen/CGExpr.cpp:3700
+    return false;
+  if (auto *BaseDecl = E->getType()->getPointeeType()->getAsRecordDecl())
+    return hasBPFPreserveStaticOffset(BaseDecl);
----------------
eddyz87 wrote:
> erichkeane wrote:
> > getPointeeType can also return nullptr, so unless you have a test elsewhere to ensure it isn't, you likely have to do a little more work here (and if so, I'd need an assert).
> Is it? I actually double-checked this before pushing an update, clangd jumps to the following definition:
> 
> ```
> lang=cpp
> QualType Type::getPointeeType() const {
>   if (const auto *PT = getAs<PointerType>())
>     return PT->getPointeeType();
>   ...
>   return {};
> }
> ```
> 
> The `getAsRecordDecl()` can return null indeed, but that null is checked.
More correctly, it returns an empty `QualType`.  The `operator->` on that will cause a `nullptr`, causing the call to `Type::getAsRecordDecl` to have a `nullptr` `this`.


================
Comment at: llvm/test/CodeGen/BPF/preserve-static-offset/load-align.ll:61
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"clang version 18.0.0 (/home/eddy/work/llvm-project/clang c899a1ca75d0f1b559204eff79a2578d2cafc7ab)"}
+!2 = !{!3, !4, i64 128}
----------------
eddyz87 wrote:
> erichkeane wrote:
> > Are we sure we want to do something like this?  It seems this both depends on YOUR computer AND us never releasing Clang 18.
> Are you sure this would be an issue?
> The specific line is not a part of a CHECK and I tried the following command using my system's llvm 16 opt:
> 
> ```
> opt -O2 -mtriple=bpf-pc-linux -S -o - load-align.ll
> ```
> 
> And module was loaded / processed w/o any issues.
> In general grepping shows that people don't usually mask these in tests:
> 
> ```
> $ cd llvm/test/CodeGen/
> $ ag '{!"clang version' | wc -l
> 452
> ```
I don't write LLVM tests ever, so I'm not sure.  It just seems odd to provide that much irrelevant info, perhaps one of hte LLVM reviewers can comment.  Also, look at those ~450 and see what they contain?


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D133361/new/

https://reviews.llvm.org/D133361