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* [PATCH v3] i386: Allow -mlarge-data-threshold with -mcmodel=large
@ 2023-06-13  3:28 Fangrui Song
  2023-06-13  6:16 ` Jan Beulich
  0 siblings, 1 reply; 4+ messages in thread
From: Fangrui Song @ 2023-06-13  3:28 UTC (permalink / raw)
  To: gcc-patches, Florian Weimer, H.J. Lu, Jan Beulich, Jan Hubicka,
	Michael Matz, Uros Bizjak
  Cc: Fangrui Song

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


^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-06-24  2:29 UTC | newest]

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-- links below jump to the message on this page --
2023-06-13  3:28 [PATCH v3] i386: Allow -mlarge-data-threshold with -mcmodel=large Fangrui Song
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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