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

Message ID 20231016182138.1304513-1-maskray@google.com
State New
Headers show
Series [v5] i386: Allow -mlarge-data-threshold with -mcmodel=large | expand

Commit Message

Fangrui Song Oct. 16, 2023, 6:21 p.m. UTC 
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 mbox series

Patch

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];