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gimplify: Don't optimize register const vars to static [PR93949]

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The following testcase is rejected, while it was accepted in 3.4 and earlier
(before tree-ssa merge).
The problem is that we decide to promote the const variable to TREE_STATIC,
but TREE_STATIC DECL_REGISTER VAR_DECLs may only be the global register vars
and so assemble_variable/make_decl_rtl diagnoses it.

Either we do what the following patch does, where we could consider
register as a hint the user doesn't want such optimization, because if
something is forced static, it is not "register" anymore and register static
is not valid in C either, or we could clear DECL_REGISTER instead, but would
still need to punt at least on DECL_HARD_REGISTER cases.

2020-02-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/93949
	* gimplify.c (gimplify_init_constructor): Don't promote readonly
	DECL_REGISTER variables to TREE_STATIC.

	* gcc.c-torture/compile/pr93949.c: New test.
This commit is contained in:
Jakub Jelinek 2020-02-27 10:45:30 +01:00
parent 5f9cd512c4
commit 1956773cc6
4 changed files with 15 additions and 0 deletions
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4
gcc/ChangeLog
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@ -1,5 +1,9 @@
2020-02-27 Jakub Jelinek <jakub@redhat.com>
PR c/93949
* gimplify.c (gimplify_init_constructor): Don't promote readonly
DECL_REGISTER variables to TREE_STATIC.
PR tree-optimization/93582
PR tree-optimization/93945
* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle memset with

1
gcc/gimplify.c
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@ -4923,6 +4923,7 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
&& num_nonzero_elements > 1
&& TREE_READONLY (object)
&& VAR_P (object)
&& !DECL_REGISTER (object)
&& (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object))
/* For ctors that have many repeated nonzero elements
represented through RANGE_EXPRs, prefer initializing

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gcc/testsuite/ChangeLog
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@ -1,5 +1,8 @@
2020-02-27 Jakub Jelinek <jakub@redhat.com>
PR c/93949
* gcc.c-torture/compile/pr93949.c: New test.
PR tree-optimization/93582
PR tree-optimization/93945
* gcc.dg/tree-ssa/pr93582-9.c: New test.

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gcc/testsuite/gcc.c-torture/compile/pr93949.c Normal file
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@ -0,0 +1,7 @@
/* PR c/93949 */
void
foo (void)
{
register const double d[3] = { 0., 1., 2. };
}