i386: Allow -mlarge-data-threshold with -mcmodel=large

From: Fangrui Song <maskray@google.com>

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>
gcc/ChangeLog:

	* config/i386/i386.cc (ix86_can_inline_p):
	Handle CM_LARGE and CM_LARGE_PIC.
	(x86_elf_aligned_decl_common): Ditto.
	(x86_output_aligned_bss): Ditto.
	* config/i386/i386.opt: Update doc for -mlarge-data-threshold=.
	* doc/invoke.texi: Update doc for -mlarge-data-threshold=.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/large-data.c: New test.

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 8251b67e2d6d74825167c5f26b078b0fdb576af8..641e768033553be716299de01b158e403048382a 100644 (file)
--- 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 b8382c4809988df8f167b0e93b3919594d42cd6e..0c3b8f4b62189f7d1dfc253b3e1c62fa0894bd7f 100644 (file)
--- 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 a26dc5aae69ff4fbd4914f6ac10362bda378ef00..2a500c1baeea25003eaf8be4d2dde6716f9aba2a 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -33398,9 +33398,9 @@ 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 (file)
index 0000000..bdd4acd
--- /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];