From: Fangrui Song <maskray@google.com>
To: gcc-patches@gcc.gnu.org, Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jan Beulich <jbeulich@suse.com>,
Jan Hubicka <hubicka@ucw.cz>, Michael Matz <matz@suse.de>,
Uros Bizjak <ubizjak@gmail.com>
Cc: Fangrui Song <maskray@google.com>
Subject: [PATCH v3] i386: Allow -mlarge-data-threshold with -mcmodel=large
Date: Mon, 12 Jun 2023 20:28:23 -0700 [thread overview]
Message-ID: <20230613032823.264347-1-maskray@google.com> (raw)
When using -mcmodel=medium, large data objects larger than the
-mlarge-data-threshold threshold are placed into large data sections
(.lrodata, .ldata, .lbss and some variants). GNU ld and ld.lld 17 place
.l* sections into separate output sections. If small and medium code
model object files are mixed, the .l* sections won't exert relocation
overflow pressure on sections in object files built with -mcmodel=small.
However, when using -mcmodel=large, -mlarge-data-threshold doesn't
apply. This means that the .rodata/.data/.bss sections may exert
relocation overflow pressure on sections in -mcmodel=small object files.
This patch allows -mcmodel=large to generate .l* sections and drops an
unneeded documentation restriction that the value must be the same.
Link: https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU
("Large data sections for the large code model")
Signed-off-by: Fangrui Song <maskray@google.com>
---
Changes from v1 (https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616947.html):
* Clarify commit message. Add link to https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU
Changes from v2
* Drop an uneeded limitation in the documentation.
---
gcc/config/i386/i386.cc | 15 +++++++++------
gcc/config/i386/i386.opt | 2 +-
gcc/doc/invoke.texi | 6 +++---
gcc/testsuite/gcc.target/i386/large-data.c | 13 +++++++++++++
4 files changed, 26 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index d4ff56ee8dd..ca92a5b65ce 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -637,7 +637,8 @@ ix86_can_inline_p (tree caller, tree callee)
static bool
ix86_in_large_data_p (tree exp)
{
- if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC)
+ if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC &&
+ ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC)
return false;
if (exp == NULL_TREE)
@@ -848,8 +849,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl,
const char *name, unsigned HOST_WIDE_INT size,
unsigned align)
{
- if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
- && size > (unsigned int)ix86_section_threshold)
+ if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
+ ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
+ size > (unsigned int)ix86_section_threshold)
{
switch_to_section (get_named_section (decl, ".lbss", 0));
fputs (LARGECOMM_SECTION_ASM_OP, file);
@@ -869,9 +871,10 @@ void
x86_output_aligned_bss (FILE *file, tree decl, const char *name,
unsigned HOST_WIDE_INT size, unsigned align)
{
- if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
- && size > (unsigned int)ix86_section_threshold)
- switch_to_section (get_named_section (decl, ".lbss", 0));
+ if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
+ ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
+ size > (unsigned int)ix86_section_threshold)
+ switch_to_section(get_named_section(decl, ".lbss", 0));
else
switch_to_section (bss_section);
ASM_OUTPUT_ALIGN (file, floor_log2 (align / BITS_PER_UNIT));
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index d74f6b1f8fc..de8e722cd62 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -282,7 +282,7 @@ Branches are this expensive (arbitrary units).
mlarge-data-threshold=
Target RejectNegative Joined UInteger Var(ix86_section_threshold) Init(DEFAULT_LARGE_SECTION_THRESHOLD)
--mlarge-data-threshold=<number> Data greater than given threshold will go into .ldata section in x86-64 medium model.
+-mlarge-data-threshold=<number> Data greater than given threshold will go into a large data section in x86-64 medium and large code models.
mcmodel=
Target RejectNegative Joined Enum(cmodel) Var(ix86_cmodel) Init(CM_32)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 9130104af22..a31f33e7193 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -33006,9 +33006,9 @@ the cache line size. @samp{compat} is the default.
@opindex mlarge-data-threshold
@item -mlarge-data-threshold=@var{threshold}
-When @option{-mcmodel=medium} is specified, data objects larger than
-@var{threshold} are placed in the large data section. This value must be the
-same across all objects linked into the binary, and defaults to 65535.
+When @option{-mcmodel=medium} or @option{-mcmodel=large} is specified, data
+objects larger than @var{threshold} are placed in large data sections. The
+default is 65535.
@opindex mrtd
@item -mrtd
diff --git a/gcc/testsuite/gcc.target/i386/large-data.c b/gcc/testsuite/gcc.target/i386/large-data.c
new file mode 100644
index 00000000000..09a917431d4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/large-data.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-O2 -mcmodel=large -mlarge-data-threshold=4" } */
+/* { dg-final { scan-assembler ".lbss" } } */
+/* { dg-final { scan-assembler ".bss" } } */
+/* { dg-final { scan-assembler ".ldata" } } */
+/* { dg-final { scan-assembler ".data" } } */
+/* { dg-final { scan-assembler ".lrodata" } } */
+/* { dg-final { scan-assembler ".rodata" } } */
+
+const char rodata_a[] = "abc", rodata_b[] = "abcd";
+char data_a[4] = {1}, data_b[5] = {1};
+char bss_a[4], bss_b[5];
--
2.41.0.162.gfafddb0af9-goog
next reply other threads:[~2023-06-13 3:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-13 3:28 Fangrui Song [this message]
2023-06-13 6:16 ` Jan Beulich
2023-06-13 21:49 ` Fangrui Song
2023-06-24 2:29 ` Fangrui Song
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