This patch allows a function to request clearing of all instruction and execution
hazards upon normal return via __attribute__ ((use_hazard_barrier_return)).
2017-04-25 Prachi Godbole <prachi.godbole@imgtec.com>
gcc/ChangeLog:
* 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.cc (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/ChangeLog:
* gcc.target/mips/hazard-barrier-return-attribute.c: New test.
Signed-off-by: Junxian Zhu <zhujunxian@oss.cipunited.com>
mips_handle_use_shadow_register_set_attr, NULL },
{ "keep_interrupts_masked", 0, 0, false, true, true, false, NULL, NULL },
{ "use_debug_exception_return", 0, 0, false, true, true, false, NULL, NULL },
+ { "use_hazard_barrier_return", 0, 0, true, false, false, false, NULL, NULL },
{ NULL, 0, 0, false, false, false, false, NULL, NULL }
};
\f
/* 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
;; The `.insn' pseudo-op.
UNSPEC_INSN_PSEUDO
+ UNSPEC_JRHB
])
(define_constants
[(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"
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 a 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
--- /dev/null
+/* Test attribute for clearing hazards while returning. */
+/* { dg-do compile } */
+/* { dg-options "isa_rev>=2 -mno-mips16" } */
+
+extern int bar ();
+
+static int __attribute__ ((use_hazard_barrier_return))
+foo0 ()
+{
+ return bar ();
+}
+
+int
+foo1 ()
+{
+ return foo0 ();
+}
+
+/* { dg-final { scan-assembler "foo0:" } } */
+/* { dg-final { scan-assembler-times "\tjr.hb\t\\\$31\n\tnop\\n" 1 } } */