This patch adds support for function attribute __attribute__
((use_hazard_barrier_return)). The attribute will generate hazard barrier
return (jr.hb) instead of a normal return instruction.
Changelog:
2017-04-25 Prachi Godbole <prachi.godb...@imgtec.com>
gcc/
* config/mips/mips.h (machine_function): New variable
use_hazard_barrier_return_p.
* config/mips/mips.md (UNSPEC_JRHB): New unspec.
(mips_hb_return_internal): New insn pattern.
* config/mips/mips.c (mips_attribute_table): Add attribute
use_hazard_barrier_return.
(mips_use_hazard_barrier_return_p): New static function.
(mips_function_attr_inlinable_p): Likewise.
(mips_compute_frame_info): Set use_hazard_barrier_return_p. Emit error
for unsupported architecture choice.
(mips_function_ok_for_sibcall, mips_can_use_return_insn): Return false
for use_hazard_barrier_return.
(mips_expand_epilogue): Emit hazard barrier return.
* doc/extend.texi: Document use_hazard_barrier_return.
gcc/testsuite/
* gcc.target/mips/hazard-barrier-return-attribute.c: New test.
Ok for stage1?
Regards,
Prachi
Index: gcc/doc/extend.texi
===================================================================
--- gcc/doc/extend.texi (revision 246899)
+++ gcc/doc/extend.texi (working copy)
@@ -4496,6 +4496,12 @@ On MIPS targets, you can use the @code{nocompressi
to locally turn off MIPS16 and microMIPS code generation. This attribute
overrides the @option{-mips16} and @option{-mmicromips} options on the
command line (@pxref{MIPS Options}).
+
+@item use_hazard_barrier_return
+@cindex @code{use_hazard_barrier_return} function attribute, MIPS
+This function attribute instructs the compiler to generate hazard barrier
return
+that clears all execution and instruction hazards while returning, instead of
+generating a normal return instruction.
@end table
@node MSP430 Function Attributes
Index: gcc/config/mips/mips.md
===================================================================
--- gcc/config/mips/mips.md (revision 246899)
+++ gcc/config/mips/mips.md (working copy)
@@ -156,6 +156,7 @@
;; The `.insn' pseudo-op.
UNSPEC_INSN_PSEUDO
+ UNSPEC_JRHB
])
(define_constants
@@ -6578,6 +6579,20 @@
[(set_attr "type" "jump")
(set_attr "mode" "none")])
+;; Insn to clear execution and instruction hazards while returning.
+;; However, it doesn't clear hazards created by the insn in its delay slot.
+;; Thus, explicitly place a nop in its delay slot.
+
+(define_insn "mips_hb_return_internal"
+ [(return)
+ (unspec_volatile [(match_operand 0 "pmode_register_operand" "")]
+ UNSPEC_JRHB)]
+ ""
+ {
+ return "%(jr.hb\t$31%/%)";
+ }
+ [(set_attr "insn_count" "2")])
+
;; Normal return.
(define_insn "<optab>_internal"
Index: gcc/config/mips/mips.c
===================================================================
--- gcc/config/mips/mips.c (revision 246899)
+++ gcc/config/mips/mips.c (working copy)
@@ -615,6 +615,7 @@ static const struct attribute_spec mips_attribute_
mips_handle_use_shadow_register_set_attr, false },
{ "keep_interrupts_masked", 0, 0, false, true, true, NULL, false },
{ "use_debug_exception_return", 0, 0, false, true, true, NULL, false },
+ { "use_hazard_barrier_return", 0, 0, true, false, false, NULL, false },
{ NULL, 0, 0, false, false, false, NULL, false }
};
@@ -1275,6 +1276,16 @@ mips_use_debug_exception_return_p (tree type)
TYPE_ATTRIBUTES (type)) != NULL;
}
+/* Check if the attribute to use hazard barrier return is set for
+ the function declaration DECL. */
+
+static bool
+mips_use_hazard_barrier_return_p (tree decl)
+{
+ return lookup_attribute ("use_hazard_barrier_return",
+ DECL_ATTRIBUTES (decl)) != NULL;
+}
+
/* Return the set of compression modes that are explicitly required
by the attributes in ATTRIBUTES. */
@@ -1460,6 +1471,21 @@ mips_can_inline_p (tree caller, tree callee)
return default_target_can_inline_p (caller, callee);
}
+/* Implement TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P.
+
+ A function reqeuesting clearing of all instruction and execution hazards
+ before returning cannot be inlined - thereby not clearing any hazards.
+ All our other function attributes are related to how out-of-line copies
+ should be compiled or called. They don't in themselves prevent inlining.
*/
+
+static bool
+mips_function_attr_inlinable_p (const_tree decl)
+{
+ if (mips_use_hazard_barrier_return_p (const_cast<tree>(decl)))
+ return false;
+ return hook_bool_const_tree_true (decl);
+}
+
/* Handle an "interrupt" attribute with an optional argument. */
static tree
@@ -7863,6 +7889,11 @@ mips_function_ok_for_sibcall (tree decl, tree exp
&& !targetm.binds_local_p (decl))
return false;
+ /* Can't generate sibling calls if returning from current function using
+ hazard barrier return. */
+ if (mips_use_hazard_barrier_return_p (current_function_decl))
+ return false;
+
/* Otherwise OK. */
return true;
}
@@ -10943,6 +10974,17 @@ mips_compute_frame_info (void)
}
}
+ /* Determine whether to use hazard barrier return or not. */
+ if (mips_use_hazard_barrier_return_p (current_function_decl))
+ {
+ if (mips_isa_rev < 2)
+ error ("hazard barrier return requires MIPS ISA to be R2 or greater");
+ else if (TARGET_MIPS16)
+ error ("hazard barrier return cannot be used with MIPS16 functions");
+ else
+ cfun->machine->use_hazard_barrier_return_p = true;
+ }
+
frame = &cfun->machine->frame;
memset (frame, 0, sizeof (*frame));
size = get_frame_size ();
@@ -12606,7 +12648,8 @@ mips_expand_epilogue (bool sibcall_p)
&& !crtl->calls_eh_return
&& !sibcall_p
&& step2 > 0
- && mips_unsigned_immediate_p (step2, 5, 2))
+ && mips_unsigned_immediate_p (step2, 5, 2)
+ && !cfun->machine->use_hazard_barrier_return_p)
use_jraddiusp_p = true;
else
/* Deallocate the final bit of the frame. */
@@ -12647,6 +12690,11 @@ mips_expand_epilogue (bool sibcall_p)
else
emit_jump_insn (gen_mips_eret ());
}
+ else if (cfun->machine->use_hazard_barrier_return_p)
+ {
+ rtx reg = gen_rtx_REG (Pmode, RETURN_ADDR_REGNUM);
+ emit_jump_insn (gen_mips_hb_return_internal (reg));
+ }
else
{
rtx pat;
@@ -12705,6 +12753,11 @@ mips_can_use_return_insn (void)
if (cfun->machine->interrupt_handler_p)
return false;
+ /* Even if the function has a null epilogue, generating hazard barrier return
+ in epilogue handler is a lot cleaner and more manageable. */
+ if (cfun->machine->use_hazard_barrier_return_p)
+ return false;
+
if (!reload_completed)
return false;
@@ -22476,10 +22529,9 @@ mips_promote_function_mode (const_tree type ATTRIB
#undef TARGET_ATTRIBUTE_TABLE
#define TARGET_ATTRIBUTE_TABLE mips_attribute_table
-/* All our function attributes are related to how out-of-line copies should
- be compiled or called. They don't in themselves prevent inlining. */
+
#undef TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P
-#define TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P hook_bool_const_tree_true
+#define TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P mips_function_attr_inlinable_p
#undef TARGET_EXTRA_LIVE_ON_ENTRY
#define TARGET_EXTRA_LIVE_ON_ENTRY mips_extra_live_on_entry
Index: gcc/config/mips/mips.h
===================================================================
--- gcc/config/mips/mips.h (revision 246899)
+++ gcc/config/mips/mips.h (working copy)
@@ -3405,6 +3405,9 @@ struct GTY(()) machine_function {
/* True if GCC stored callee saved registers in the frame header. */
bool use_frame_header_for_callee_saved_regs;
+
+ /* True if the function should generate hazard barrier return. */
+ bool use_hazard_barrier_return_p;
};
#endif
Index: gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
===================================================================
--- gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
(revision 0)
+++ gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
(revision 0)
@@ -0,0 +1,13 @@
+/* Test attribute for clearing hazards while returning. */
+/* { dg-do compile } */
+/* { dg-options "isa_rev>=2 -mno-mips16" } */
+
+extern int bar ();
+
+int __attribute__ ((use_hazard_barrier_return))
+foo ()
+{
+ return bar ();
+}
+/* { dg-final { scan-assembler "\tjr.hb\t$31\n" } } */
+/* { dg-final { scan-assembler "\tnop\n" } } */
