[PATCH #2/4] c++: mark short-enums as packed

[Alexandre Oliva <oliva@adacore.com>]

Unlike C, C++ doesn't mark enums shortened by -fshort-enums as packed.
This makes for undesirable warning differences between C and C++,
e.g. c-c++-common/analyzer/null-deref-pr108251-smp_fetch_ssl_fc_has_early*.c
triggers a warning about a type cast from a pointer to enum that, when
packed, might not be sufficiently aligned.

This change is not enough for that warning to trigger.  The tree
expression generated by the C++ front-end is also a little too
complicated for us get to the base pointer.  A separate patch takes
care of that.

Regstrapped on x86_64-linux-gnu, also tested on arm-eabi with default
cpu on trunk, and with tms570 on gcc-13.  Ok to install?


for  gcc/cp/ChangeLog

	* decl.cc (finish_enum_value_list): Set TYPE_PACKED if
	use_short_enum, and propagate it to variants.
---
 gcc/cp/decl.cc |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 038c5ab71f201..f6d5645d5080f 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -16881,6 +16881,12 @@ finish_enum_value_list (tree enumtype)
       /* If -fstrict-enums, still constrain TYPE_MIN/MAX_VALUE.  */
       if (flag_strict_enums)
 	set_min_and_max_values_for_integral_type (enumtype, precision, sgn);
+
+      if (use_short_enum)
+	{
+	  TYPE_PACKED (enumtype) = use_short_enum;
+	  fixup_attribute_variants (enumtype);
+	}
     }
   else
     underlying_type = ENUM_UNDERLYING_TYPE (enumtype);


-- 
Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
   Free Software Activist                   GNU Toolchain Engineer
More tolerance and less prejudice are key for inclusion and diversity
Excluding neuro-others for not behaving ""normal"" is *not* inclusive