RE: [PATCH] Add IEEE FLOAT128 support to test gdb.base/whatis-ptype-typedefs.exp

[Carl Love <cel@us.ibm.com>]

On Mon, 2022-07-18 at 16:22 +0100, Pedro Alves wrote:
> On 2022-07-13 8:38 p.m., Carl Love via Gdb-patches wrote:
> 
> > GCC enabled IEEE FLOAT 128-bit support starting with GCC 12 by
> > default.
> > Previously long double was the default for 128-bit floating point
> > support.
> > This patch updates the expected result for the "long doube" tests
> > to
> > _Float128 if GCC 12 is used.  The previous "long double" result is
> > expected for GCC 11 and older versions.
> 
> This whole paragraph reads as if all archs were changed, but it was
> just Power, right?

Yes, it should say the default on PowerPC changed to IEEE.  

Per comments from Ulrich, I need to investigate further to figure out
where the _Float128 is coming from as the string doesn't occur in the
source code.  From my initial look, I don't see the string in the gdb
code or the test case source code, the source DWARF or objdump output. 
In function check_typedef (gdb/gdbtpyes.c) there is a while loop that
iterates thru the type removing the typedefs.  Initially the type->name 
= long_double_typedef but then changes to _Float128.  I don't know
where the typedef all gets setup but I would think it comes from
reading the source code DWARF.  Anyway, I am working on figuring out
where and how the _Float128 gets setup.  
> 
> And isn't it the case that after the change, for GCC, "long double"
> _IS_ IEEE FLOAT 128-bit?
> 
> Doesn't that mean that GCC and GDB now have a mismatch of what they
> think "long double" is?
> Like for example, if the user copies an expression from their program
> and evaluates in gdb,
> and that expression uses "long double", then GDB will evaluate it
> differently from how GCC would?
> 
> Shouldn't GDB instead adjust its "long double" type depending on the
> ABI, mapping "long double"
> to the right format?  And then, the testcase (probably) wouldn't
> change?
> 
> BTW, I was expecting to see GCC's default change mentioned at:
> 
>   
> https://gcc.gnu.org/gcc-12/changes.html
>  
> 
> but I can't seem to find it there, other than a Fortran reference
> which seems related.  I did find:
> 
>   
> https://gcc.gnu.org/wiki/Ieee128PowerPC#Transition
>  
> 
> > The patch has been run on Power 7 (gcc version 4.8.5), Power 10
> > (gcc
> > version 12.1) and Intel x86_64 (gcc version 11.2.0) to verify the
> > patch
> > fixes the 74 test failures on Power 10 with GCC 12 and does not
> > introduce
> > any regression failures on older versions of GCC.
> 
> Seems like x86 with gcc 12 would better be tested as well.
> 
> > ---
> >  .../gdb.base/whatis-ptype-typedefs.exp        | 26 ++++++++++++++-
> > ----
> >  1 file changed, 20 insertions(+), 6 deletions(-)
> > 
> > diff --git a/gdb/testsuite/gdb.base/whatis-ptype-typedefs.exp
> > b/gdb/testsuite/gdb.base/whatis-ptype-typedefs.exp
> > index be76183ca79..a17084a19ec 100644
> > --- a/gdb/testsuite/gdb.base/whatis-ptype-typedefs.exp
> > +++ b/gdb/testsuite/gdb.base/whatis-ptype-typedefs.exp
> > @@ -77,6 +77,12 @@ proc prepare {lang} {
> >  #
> >  # This can be "c" or "c++".
> >  #
> > +
> > +# GCC 12 uses IEEE 128-bit floating point as the default starting
> > with GCC 12.
> 
> On all archs?
> 
> > +# The table below consists of the compiler independent tests.  The
> > GCC version
> > +# specific tests are appended to the end of the table based on the
> > compiler
> > +# version.
> > +
> >  # Columns in the table represent:
> >       # EXP                # whatis           # ptype           #
> > language
> >  set table {
> > @@ -97,12 +103,6 @@ set table {
> >      {"double_typedef2"    "double_typedef"   "double"}
> >      {"v_double_typedef"   "double_typedef"   "double"}
> >      {"v_double_typedef2"  "double_typedef2"  "double"}
> > -
> > -    {"long_double_typedef"    "long double"           "long
> > double"}
> > -    {"long_double_typedef2"   "long_double_typedef"   "long
> > double"}
> > -    {"v_long_double_typedef"  "long_double_typedef"   "long
> > double"}
> > -    {"v_long_double_typedef2" "long_double_typedef2"  "long
> > double"}
> > -
> >      {"colors_typedef"     "(enum )?colors"   "enum colors( :
> > unsigned int)? {red, green, blue}"}
> >      {"colors_typedef2"    "colors_typedef"   "enum colors( :
> > unsigned int)? {red, green, blue}"}
> >      {"v_colors_typedef"   "colors_typedef"   "enum colors( :
> > unsigned int)? {red, green, blue}"}
> > @@ -151,6 +151,20 @@ set table {
> >  	"c++"}
> >  }
> >  
> > +# Add the long double tests on the version of GCC
> > +if { [test_compiler_info gcc-*] && [gcc_major_version] >= 12 } {
> 
> What about x86 + gcc 12 ?
> 
> > +    lappend table {"long_double_typedef"    "long
> > double"           "_Float128"}
> > +    lappend table
> > {"long_double_typedef2"   "long_double_typedef"   "_Float128"}
> > +    lappend table
> > {"v_long_double_typedef"  "long_double_typedef"   "_Float128"}
> > +    lappend table {"v_long_double_typedef2"
> > "long_double_typedef2"  "_Float128"}
> > +
> > +} else {
> > +    lappend table {"long_double_typedef"    "long
> > double"           "long double"}
> > +    lappend table
> > {"long_double_typedef2"   "long_double_typedef"   "long double"}
> > +    lappend table
> > {"v_long_double_typedef"  "long_double_typedef"   "long double"}
> > +    lappend table {"v_long_double_typedef2"
> > "long_double_typedef2"  "long double"}
> > +}
> 
>