c: Better fix for speed up compilation of large char array initializers when...

c: Better fix for speed up compilation of large char array initializers when not using #embed [PR117190]

On Wed, Oct 16, 2024 at 11:09:32PM +0200, Jakub Jelinek wrote:
> Apparently my
> c: Speed up compilation of large char array initializers when not using #embed
> patch broke building glibc.
>
> The issue is that when using CPP_EMBED, we are guaranteed by the
> preprocessor that there is CPP_NUMBER CPP_COMMA before it and
> CPP_COMMA CPP_NUMBER after it (or CPP_COMMA CPP_EMBED), so RAW_DATA_CST
> never ends up at the end of arrays of unknown length.
> Now, the c_parser_initval optimization attempted to preserve that property
> rather than changing everything that e.g. inferes array number of elements
> from the initializer etc. to deal with RAW_DATA_CST at the end, but
> it didn't take into account the possibility that there could be
> CPP_COMMA followed by CPP_CLOSE_BRACE (where the CPP_COMMA is redundant).
>
> As we are peaking already at 4 tokens in that code, peeking more would
> require using raw tokens and that seems to be expensive doing it for
> every pair of tokens due to vec_free done when we are out of raw tokens.

Sorry for rushing the previous patch too much, turns out I was wrong,
given that the c_parser_peek_nth_token numbering is 1 based, we can peek
also with c_parser_peek_nth_token (parser, 4) and the loop actually peeked
just at 3 tokens, not 4.

So, I think it is better to revert the previous patch (but keep the new
test) and instead peek the 4th non-raw token, which is what the following
patch does.

Additionally, PR117190 shows one further spot which missed the peek of
the token after CPP_COMMA, in case it is incomplete array with exactly 65
elements with redundant comma after it, which this patch handles too.

2024-10-22  Jakub Jelinek  <jakub@redhat.com>

	PR c/117190
gcc/c/
	* c-parser.cc (c_parser_initval): Revert 2024-10-17 changes.
	Instead peek the 4th token and if it is not CPP_NUMBER,
	handle it like 3rd token CPP_CLOSE_BRACE for orig_len == INT_MAX.
	Also, check (2 + 2 * i)th raw token for the orig_len == INT_MAX
	case and punt if it is not CPP_NUMBER.
gcc/testsuite/
	* c-c++-common/init-5.c: New test.