[PATCH] D112626: Convert float to double on __builtin_dump_struct

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:2090-2094
+    // Variadic functions expect the caller to promote float to double.
+    if (CanonicalType == Context.FloatTy) {
+      FieldPtr =
+          CGF.Builder.CreateFPExt(FieldPtr, CGF.ConvertType(Context.DoubleTy));
+    }
----------------
rjmccall wrote:
> aaron.ballman wrote:
> > This change is an improvement as far as it goes, but I think we might be missing other floating-point promotions here. For example, `__fp16` fields also seem to be unusable: https://godbolt.org/z/z3a45f9YE
> > 
> > Also, we don't seem to handle the integer promotions at all (but still get correct results there), so I think we're getting the correct behavior there by chance rather than by design. Oh, yeah, note the differences here: https://godbolt.org/z/f13eq3668
> > 
> > ```
> > foo:
> >   ...
> >   %7 = load i8, i8* %4, align 1, !dbg !217
> >   %8 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @2, i32 0, i32 0), i8 %7), !dbg !217
> >   ...
> > 
> > bar:
> >   ...
> >   %2 = load i8, i8* %1, align 1, !dbg !222
> >   %3 = zext i8 %2 to i32, !dbg !222
> >   %4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %3), !dbg !223
> >   ...
> > ```
> > I think we should probably fix all of the promotion problems at once rather than piecemeal.
> > 
> It's actually really annoying that this logic has to be duplicated in IRGen instead of being able to take advantage of the existing promotion logic in Sema.  Can we just generate a helper function in Sema and somehow link it to the builtin call?
> 
> Um.  Also, the `static` local DenseMap in the code above this is totally unacceptable and should not have been committed.  Clang is supposed to be embeddable as a library and should not be using global mutable variables.
> It's actually really annoying that this logic has to be duplicated in IRGen instead of being able to take advantage of the existing promotion logic in Sema. Can we just generate a helper function in Sema and somehow link it to the builtin call?

That seems worth a shot but I think it is not something that needs to happen for this patch (that could be a rather heavy lift to ask someone who just joined the community) unless the basic fix starts getting out of hand.

> Um. Also, the static local DenseMap in the code above this is totally unacceptable and should not have been committed. Clang is supposed to be embeddable as a library and should not be using global mutable variables.

We do that with some degree of frequency already (command line arguments using `llvm::cl::opt` are all global mutable variables, such as https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CoverageMappingGen.cpp#L34), but yeah, fixing that up would also not be a bad idea, but orthogonal to this patch IMO.


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  https://reviews.llvm.org/D112626/new/

https://reviews.llvm.org/D112626