Re: [PATCH] rs6000: Don't ICE when we disassemble an MMA variable [PR101322]

[Peter Bergner <bergner@linux.ibm.com>]

On 8/31/22 3:51 PM, Segher Boessenkool wrote:
> On Wed, Aug 31, 2022 at 01:53:48PM -0500, Peter Bergner wrote:
>> Question for my own education, when would you use VIEW_CONVERT_EXPR over NOP_EXPR?
> 
> VIEW_CONVERT_EXPR is essentially a bit_cast.  Only use it when you need
> that, it is sub-optimal if you don't.

Ok.  I believe I added a couple of other similar uses of VIEW_CONVERT_EXPR for
pointer casts on the __builtin_vsx_lxvp/stxvp built-ins.  I'll try converting
those to use NOP_EXPR too in a separate cleanup patch.  Thanks!



>> -      tree src_type = TREE_TYPE (src_ptr);
>> +      tree src_type = (fncode == RS6000_BIF_DISASSEMBLE_ACC)
>> +                     ? ptr_vector_quad_type_node : ptr_vector_pair_type_node;
> 
> If you split a?b:c over multiple lines, please make it three lines.

Can do, however...


>> ...and of course, now I can't recreate that issue at all and the
>> ptr_vector_*_type use work fine now.  Strange! ...so ok, changed.
>> Maybe the behavior changed since my PR106017 fix went in???
> 
> That is my best guess as well.  But, how did that help this test?

It didn't. :-)   During my bootstrap, I hit the gimple verification issue
I mentioned seeing earlier.  My problem was I thought I hit it with the
test case, but it was exposed on a different test case in the testsuite.
Here's what I'm seeing, which only happens when using -O0 -flto:

rain6p1% gcc -O0 -mcpu=power10 -flto pr102347.c 
lto1: internal compiler error: in gimple_canonical_types_compatible_p, at tree.cc:13677
0x11930a97 gimple_canonical_types_compatible_p(tree_node const*, tree_node const*, bool)
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/tree.cc:13677
0x1192f1ab verify_type_variant
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/tree.cc:13377
0x11930beb verify_type(tree_node const*)
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/tree.cc:13700
0x106bbd37 lto_fixup_state
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/lto/lto-common.cc:2629
0x106bbff3 lto_fixup_decls
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/lto/lto-common.cc:2660
0x106bce13 read_cgraph_and_symbols(unsigned int, char const**)
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/lto/lto-common.cc:2901
0x1067bcbf lto_main()
	/home/bergner/gcc/gcc-fsf-mainline-pr101322/gcc/lto/lto.cc:656
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
lto-wrapper: fatal error: /home/bergner/gcc/build/gcc-fsf-mainline-pr101322-debug/gcc/xgcc returned 1 exit status
compilation terminated.
/home/bergner/binutils/install/binutils-power10/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status

The problem goes away if I use use -O1 or above, I drop -flto or I use
the code I originally posted without the ptr_vector_*_type

The assert in gimple_canonical_types_compatible_p() we're hitting is:
13673	    default:
13674	      /* Consider all types with language specific trees in them mutually
13675		 compatible.  This is executed only from verify_type and false
13676	         positives can be tolerated.  */
13677	      gcc_assert (!in_lto_p);
13678	      return true;

I have no idea why ptr_vector_*_type would behave differently here than
build_pointer_type (vector_*_type_node).  Using the build_pointer_type()
fixed it for me, so that's why I went with it. :-)  Maybe this is a bug
in lto???

Peter