https://gcc.gnu.org/g:14ad799ae1545569be158b00865f6f2f951657bd
commit r16-3117-g14ad799ae1545569be158b00865f6f2f951657bd
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date: Thu Aug 7 12:18:38 2025 -0700
varasm: Redo mergeable section support [PR121438]
We increased the switch conversion array decl alignment
for better mergeability but it turns out that we increase
the alignment on targets which don't support mergeable sections
(e.g. NVPTX). Also after the fix for PR 121394, it becomes
obvious that we can place any sized into the mergeable section
instead of increasing the alignment.
This implements that and now also fixes PR 121438 as we don't
need to increase the alignment for the mergeable decls that
were being created by the C++ front-end.
Bootstrapped and tested on x86_64-linux-gnu.
PR middle-end/121438
PR middle-end/121444
gcc/ChangeLog:
* output.h (MAX_ALIGN_MERGABLE): Rename to ...
(MAX_MERGEABLE_BITSIZE): This.
* tree-switch-conversion.cc (switch_conversion::build_one_array):
Don't
increase the alignment.
* varasm.cc (mergeable_string_section): Use MAX_MERGEABLE_BITSIZE
instead of MAX_ALIGN_MERGABLE. Also replace `/ 8` with `/
BITS_PER_UNIT`.
(mergeable_constant_section): Select the mergeable section based on
the bitsize rather than the alignment. Make sure the align is less
than the entity size.
Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
Diff:
---
gcc/output.h | 4 ++--
gcc/tree-switch-conversion.cc | 12 +-----------
gcc/varasm.cc | 18 ++++++++++--------
3 files changed, 13 insertions(+), 21 deletions(-)
diff --git a/gcc/output.h b/gcc/output.h
index 51c2d36f8f66..835a259f71bc 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -545,8 +545,8 @@ extern GTY(()) section *bss_noswitch_section;
extern GTY(()) section *in_section;
extern GTY(()) bool in_cold_section_p;
-/* MAX bit alignment for mergable sections. */
-#define MAX_ALIGN_MERGABLE 256
+/* MAX size for mergeable sections in bits. */
+#define MAX_MERGEABLE_BITSIZE 256
extern section *get_unnamed_section (unsigned int, void (*) (const char *),
const char *);
diff --git a/gcc/tree-switch-conversion.cc b/gcc/tree-switch-conversion.cc
index 04b357fca4c4..62eddcd95d31 100644
--- a/gcc/tree-switch-conversion.cc
+++ b/gcc/tree-switch-conversion.cc
@@ -55,7 +55,6 @@ Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
MA
#include "hwint.h"
#include "internal-fn.h"
#include "diagnostic-core.h"
-#include "output.h"
/* ??? For lang_hooks.types.type_for_mode, but is there a word_mode
type in the GIMPLE type system that is language-independent? */
@@ -1031,19 +1030,10 @@ switch_conversion::build_one_array (int num, tree
arr_index_type,
TREE_CONSTANT (decl) = 1;
TREE_READONLY (decl) = 1;
DECL_IGNORED_P (decl) = 1;
- /* The decl is mergable since we don't take the address ever and
+ /* The decl is mergeable since we don't take the address ever and
just reading from it. */
DECL_MERGEABLE (decl) = 1;
- /* Increase the alignments as needed. */
- if (tree_to_uhwi (DECL_SIZE (decl)) > DECL_ALIGN (decl))
- {
- unsigned HOST_WIDE_INT s = tree_to_uhwi (DECL_SIZE (decl));
- /* Only support up to the max supported for merging. */
- if (s <= MAX_ALIGN_MERGABLE)
- SET_DECL_ALIGN (decl, HOST_WIDE_INT_1U << ceil_log2 (s));
- }
-
if (offloading_function_p (cfun->decl))
DECL_ATTRIBUTES (decl)
= tree_cons (get_identifier ("omp declare target"), NULL_TREE,
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index ee32cf1d7f69..0d78f5b384fb 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -871,7 +871,7 @@ mergeable_string_section (tree decl ATTRIBUTE_UNUSED,
if (HAVE_GAS_SHF_MERGE && flag_merge_constants
&& TREE_CODE (decl) == STRING_CST
&& TREE_CODE (TREE_TYPE (decl)) == ARRAY_TYPE
- && align <= MAX_ALIGN_MERGABLE
+ && align <= MAX_MERGEABLE_BITSIZE
&& (len = int_size_in_bytes (TREE_TYPE (decl))) > 0
&& TREE_STRING_LENGTH (decl) == len)
{
@@ -885,7 +885,7 @@ mergeable_string_section (tree decl ATTRIBUTE_UNUSED,
mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (TREE_TYPE (decl)));
modesize = GET_MODE_BITSIZE (mode);
- if (modesize >= 8 && modesize <= MAX_ALIGN_MERGABLE
+ if (modesize >= 8 && modesize <= MAX_MERGEABLE_BITSIZE
&& (modesize & (modesize - 1)) == 0)
{
if (align < modesize)
@@ -906,8 +906,8 @@ mergeable_string_section (tree decl ATTRIBUTE_UNUSED,
if (i == len - unit || (unit == 1 && i == len))
{
sprintf (name, "%s.str%d.%d", prefix,
- modesize / 8, (int) (align / 8));
- flags |= (modesize / 8) | SECTION_MERGE | SECTION_STRINGS;
+ modesize / BITS_PER_UNIT, (int) (align / BITS_PER_UNIT));
+ flags |= (modesize / BITS_PER_UNIT) | SECTION_MERGE |
SECTION_STRINGS;
return get_section (name, flags, NULL);
}
}
@@ -923,17 +923,19 @@ mergeable_constant_section (unsigned HOST_WIDE_INT
size_bits,
unsigned HOST_WIDE_INT align,
unsigned int flags)
{
+ unsigned HOST_WIDE_INT newsize;
+ newsize = HOST_WIDE_INT_1U << ceil_log2 (size_bits);
if (HAVE_GAS_SHF_MERGE && flag_merge_constants
- && size_bits <= align
+ && newsize <= MAX_MERGEABLE_BITSIZE
&& align >= 8
- && align <= MAX_ALIGN_MERGABLE
+ && align <= newsize
&& (align & (align - 1)) == 0)
{
const char *prefix = function_mergeable_rodata_prefix ();
char *name = (char *) alloca (strlen (prefix) + 30);
- sprintf (name, "%s.cst%d", prefix, (int) (align / 8));
- flags |= (align / 8) | SECTION_MERGE;
+ sprintf (name, "%s.cst%d", prefix, (int) (newsize / BITS_PER_UNIT));
+ flags |= (newsize / BITS_PER_UNIT) | SECTION_MERGE;
return get_section (name, flags, NULL);
}
return readonly_data_section;
