asavonic added inline comments.
================
Comment at: clang/test/Sema/x86-no-x87.c:48-61
+void assign2() {
+ struct st_long_double st;
+#ifndef NOERROR
+ // expected-error@+2{{long double is not supported on this target}}
+#endif
+ st.ld = 0.42;
+}
----------------
pengfei wrote:
> asavonic wrote:
> > pengfei wrote:
> > > These seems pass with GCC. https://godbolt.org/z/qM4nWhThx
> > Right. Assignment of a literal is compiled to just `mov` without any x87
> > instructions, so it is not diagnosed by GCC. On the other hand, assignment
> > of a variable does trigger the error:
> >
> > void assign4(double d) {
> > struct st_long_double st;
> > st.ld = d; // error: long double is not supported on this target
> > }
> >
> > We can update the patch to do the same for some cases, but it does not look
> > very consistent, and makes assumptions on how the code is optimized and
> > compiled.
> >
> > GCC has an advantage here, because it emits the diagnostic at a lower level
> > after at lease some optimizations are done. For example, the following code
> > does not trigger an error for GCC because of inlining:
> >
> > double get_const() {
> > return 0.42;
> > }
> > void assign5(struct st_long_double *st) {
> > st->ld = get_const();
> > }
> >
> I see. Another concern is about the 32 bits. @LiuChen3 had tested in D100091
> that GCC doesn't error for 32 bits. Do we need to consider it here?
Yes, it should be considered. Both x86 and x86_64 SysV ABI targets require x87
to be used for long double. Other targets have different requirements for long
double: double precision for Windows, double and quad precision for Android x86
and x86_64 respectively.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D98895/new/
https://reviews.llvm.org/D98895
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