[PATCH v5] i386: Allow -mlarge-data-threshold with -mcmodel=large

[Fangrui Song <maskray@google.com>]

On 2023-10-16, Uros Bizjak wrote:
>On Tue, Aug 1, 2023 at 9:51 PM Fangrui Song <maskray@google.com> wrote:
>>
>> 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.
>>
>> Changes from v3
>> * Change scan-assembler directives to use \. to match literal .
>> ---
>>  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 eabc70011ea..37e810cc741 100644
>> --- a/gcc/config/i386/i386.cc
>> +++ b/gcc/config/i386/i386.cc
>> @@ -647,7 +647,8 @@ 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)
>
>Please split multi-line expression before the operator, not after it,
>as instructed in GNU Coding Standards [1] ...
>
>[1] https://www.gnu.org/prep/standards/html_node/Formatting.html
>
>>      return false;
>>
>>    if (exp == NULL_TREE)
>> @@ -858,8 +859,9 @@ 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)
>
>... also here ...
>
>>      {
>>        switch_to_section (get_named_section (decl, ".lbss", 0));
>>        fputs (LARGECOMM_SECTION_ASM_OP, file);
>> @@ -879,9 +881,10 @@ 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)
>
>... and here.
>
>OK with these formatting changes.
>
>Thanks,
>Uros.

Thank you for the review!
Posted PATCH v5 https://gcc.gnu.org/pipermail/gcc-patches/2023-October/633153.html
with the formatting.

I don't have write access to the gcc repository:)

(Hmmm... in emacs, C-c . gnu RET C-M-\  doesn't fix the && || formatting errors.)

>> +    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 1cc8563477a..52fad492353 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 104766f446d..bf6fe3e1a20 100644
>> --- a/gcc/doc/invoke.texi
>> +++ b/gcc/doc/invoke.texi
>> @@ -33207,9 +33207,9 @@ 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..bdd4acd30b8
>> --- /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];
>> --
>> 2.41.0.585.gd2178a4bd4-goog
>>

 From da49445a50c57b583201e3fb48fa91781b9ec761 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Thu, 27 Apr 2023 12:29:31 -0700
Subject: [PATCH v5] i386: Allow -mlarge-data-threshold with -mcmodel=large

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.

Changes from v3
* Change scan-assembler directives to use \. to match literal .

Changes from v4 (https://gcc.gnu.org/pipermail/gcc-patches/2023-October/633145.html)
* "When you split an expression into multiple lines, split it before an operator, not after one."
---
  gcc/config/i386/i386.cc                    |  9 ++++++---
  gcc/config/i386/i386.opt                   |  2 +-
  gcc/doc/invoke.texi                        |  6 +++---
  gcc/testsuite/gcc.target/i386/large-data.c | 13 +++++++++++++
  4 files changed, 23 insertions(+), 7 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 8251b67e2d6..641e7680335 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -663,7 +663,8 @@ 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)
@@ -874,7 +875,8 @@ 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)
+  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));
@@ -895,7 +897,8 @@ 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)
+  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
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index b8382c48099..0c3b8f4b621 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 eb714d18511..50745a3a195 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -33390,9 +33390,9 @@ 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..bdd4acd30b8
--- /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];
-- 
2.42.0.655.g421f12c284-goog