Excerpts from Andrew Pinski's message of März 3, 2024 11:49 pm: > On Sat, Mar 2, 2024 at 5:51 PM Iain Buclaw <ibuc...@gdcproject.org> wrote: >> >> Hi, >> >> This patch fixes a wrong code issue in the D front-end where lowered >> struct comparisons would reinterpret fields with a different (usually >> bigger) alignment than the original. Use `build_aligned_type' to >> preserve the alignment when casting away for such comparisons. >> >> Bootstrapped and regression tested on x86_64-linux-gnu/-m32, committed >> to mainline, and backported to releases/gcc-13, releases/gcc-12, and >> releases/gcc-11. >> >> Regards, >> Iain. >> --- >> PR d/114171 >> >> gcc/d/ChangeLog: >> >> * d-codegen.cc (lower_struct_comparison): Keep alignment of original >> type in reinterpret cast for comparison. >> >> gcc/testsuite/ChangeLog: >> >> * gdc.dg/torture/pr114171.d: New test. >> --- >> gcc/d/d-codegen.cc | 1 + >> gcc/testsuite/gdc.dg/torture/pr114171.d | 29 +++++++++++++++++++++++++ >> 2 files changed, 30 insertions(+) >> create mode 100644 gcc/testsuite/gdc.dg/torture/pr114171.d >> >> diff --git a/gcc/d/d-codegen.cc b/gcc/d/d-codegen.cc >> index 5bc233928aa..43d7739f8fc 100644 >> --- a/gcc/d/d-codegen.cc >> +++ b/gcc/d/d-codegen.cc >> @@ -1006,6 +1006,7 @@ lower_struct_comparison (tree_code code, >> StructDeclaration *sd, >> if (tmode == NULL_TREE) >> tmode = make_unsigned_type (GET_MODE_BITSIZE (mode.require >> ())); >> >> + tmode = build_aligned_type (tmode, TYPE_ALIGN (stype)); > > You might also need to build a may_alias variant too. Or make sure the > access is using the correct aliasing set. > I have not checked if the D front-end does anything special for > aliasing sets so I am not sure if that is needed or not but I suspect > it is. >
There are no alias sets defined in the D front-end - the reference compiler doesn't enforce it, which has allowed enough code out there to expect modifying bits (eg: of a float) through a reinterpret cast (such as an int*) to just work. Thanks for the reminder though. Iain.
