From: Xi Ruoyao <xry111@xry111.site>
Date: Thu, 1 Sep 2022 10:38:14 +0000 (+0800)
Subject: LoongArch: add -mdirect-extern-access option
X-Git-Tag: basepoints/gcc-14~4774
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7742b797b3fd7acea28a0a0bff9bbb06e7c2d0ea;p=thirdparty%2Fgcc.git

LoongArch: add -mdirect-extern-access option

As a new target, LoongArch does not use copy relocation as it's
problematic in some circumstances.  One bad consequence is we are
emitting GOT for all accesses to all extern objects with default
visibility.  The use of GOT is not needed in statically linked
executables, OS kernels etc.  The GOT entry just wastes space, and the
GOT access just slow down the execution in those environments.

Before -mexplicit-relocs, we used "-Wa,-mla-global-with-pcrel" to tell
the assembler not to use GOT for extern access.  But with
-mexplicit-relocs, we have to opt the logic in GCC.

The name "-mdirect-extern-access" is learnt from x86 port.

gcc/ChangeLog:

	* config/loongarch/genopts/loongarch.opt.in: Add
	-mdirect-extern-access option.
	* config/loongarch/loongarch.opt: Regenerate.
	* config/loongarch/loongarch.cc
	(loongarch_symbol_binds_local_p): Return true if
	TARGET_DIRECT_EXTERN_ACCESS.
	(loongarch_option_override_internal): Complain if
	-mdirect-extern-access is used with -fPIC or -fpic.
	* doc/invoke.texi: Document -mdirect-extern-access for
	LoongArch.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/direct-extern-1.c: New test.
	* gcc.target/loongarch/direct-extern-2.c: New test.
---

diff --git a/gcc/config/loongarch/genopts/loongarch.opt.in b/gcc/config/loongarch/genopts/loongarch.opt.in
index ebdd9538d48d..e10618777b20 100644
--- a/gcc/config/loongarch/genopts/loongarch.opt.in
+++ b/gcc/config/loongarch/genopts/loongarch.opt.in
@@ -184,3 +184,7 @@ Enum(cmodel) String(@@STR_CMODEL_EXTREME@@) Value(CMODEL_EXTREME)
 mcmodel=
 Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel) Init(CMODEL_NORMAL)
 Specify the code model.
+
+mdirect-extern-access
+Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
+Avoid using the GOT to access external symbols.
diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 77e3a1053904..c9187bf81a7a 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -1610,6 +1610,9 @@ loongarch_weak_symbol_p (const_rtx x)
 bool
 loongarch_symbol_binds_local_p (const_rtx x)
 {
+  if (TARGET_DIRECT_EXTERN_ACCESS)
+    return true;
+
   if (SYMBOL_REF_P (x))
     return (SYMBOL_REF_DECL (x)
 	    ? targetm.binds_local_p (SYMBOL_REF_DECL (x))
@@ -6093,6 +6096,9 @@ loongarch_option_override_internal (struct gcc_options *opts)
   if (loongarch_branch_cost == 0)
     loongarch_branch_cost = loongarch_cost->branch_cost;
 
+  if (TARGET_DIRECT_EXTERN_ACCESS && flag_shlib)
+    error ("%qs cannot be used for compiling a shared library",
+	   "-mdirect-extern-access");
 
   switch (la_target.cmodel)
     {
diff --git a/gcc/config/loongarch/loongarch.opt b/gcc/config/loongarch/loongarch.opt
index 6395234218b4..96c811c850b0 100644
--- a/gcc/config/loongarch/loongarch.opt
+++ b/gcc/config/loongarch/loongarch.opt
@@ -191,3 +191,7 @@ Enum(cmodel) String(extreme) Value(CMODEL_EXTREME)
 mcmodel=
 Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel) Init(CMODEL_NORMAL)
 Specify the code model.
+
+mdirect-extern-access
+Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
+Avoid using the GOT to access external symbols.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index dd3302fcd159..9d662e353163 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1017,6 +1017,7 @@ Objective-C and Objective-C++ Dialects}.
 -memcpy  -mno-memcpy -mstrict-align -mno-strict-align @gol
 -mmax-inline-memcpy-size=@var{n} @gol
 -mexplicit-relocs -mno-explicit-relocs @gol
+-mdirect-extern-access -mno-direct-extern-access @gol
 -mcmodel=@var{code-model}}
 
 @emph{M32R/D Options}
@@ -25090,6 +25091,20 @@ GCC build-time by detecting corresponding assembler support:
 @code{-mno-explicit-relocs} otherwise.  This option is mostly useful for
 debugging, or interoperation with assemblers different from the build-time
 one.
+
+@item -mdirect-extern-access
+@itemx -mno-direct-extern-access
+@opindex mdirect-extern-access
+Do not use or use GOT to access external symbols.  The default is
+@option{-mno-direct-extern-access}: GOT is used for external symbols with
+default visibility, but not used for other external symbols.
+
+With @option{-mdirect-extern-access}, GOT is not used and all external
+symbols are PC-relatively addressed.  It is @strong{only} suitable for
+environments where no dynamic link is performed, like firmwares, OS
+kernels, executables linked with @option{-static} or @option{-static-pie}.
+@option{-mdirect-extern-access} is not compatible with @option{-fPIC} or
+@option{-fpic}.
 @end table
 
 @node M32C Options
diff --git a/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c b/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
new file mode 100644
index 000000000000..85c6c1e8a88b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-mexplicit-relocs -mdirect-extern-access" } */
+/* { dg-final { scan-assembler-not "got" } } */
+
+extern int x;
+int f() { return x; }
diff --git a/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c b/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
new file mode 100644
index 000000000000..58d8bd68a06c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-mno-explicit-relocs -mdirect-extern-access" } */
+/* { dg-final { scan-assembler-not "la.global" } } */
+
+extern int x;
+int f() { return x; }