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 ebdd9538d48dd85e17acac98ebd2dce9b875afa1..e10618777b20f28b59c2170ca33e298da0e0d07d 100644 (file)
--- 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 77e3a10539042ef970ebda9561469ba76c8de23c..c9187bf81a7a5e829fd5cf44edb380b4a51ffc53 100644 (file)
--- 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 6395234218b460504bf226f7f908c0f8cac4b8bb..96c811c850b0c024c4ca0c0005c79b8e2baf6809 100644 (file)
--- 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 dd3302fcd15971e58537cc378db87f52449b5075..9d662e353163d7bb3749f17335b55035763f2313 100644 (file)
--- 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 (file)
index 0000000..85c6c1e
--- /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 (file)
index 0000000..58d8bd6
--- /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; }