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.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.
---
Rehash of original patch posted by Prachi with minimal changes. Tested against
mips-mti-elf with mips32r2/-EB and mips32r2/-EB/-micromips.
gcc/config/mips/mips.c | 58 +++++++++++++++++--
gcc/config/mips/mips.h | 3 +
gcc/config/mips/mips.md | 15 +++++
gcc/doc/extend.texi | 6 ++
.../mips/hazard-barrier-return-attribute.c | 20 +++++++
5 files changed, 98 insertions(+), 4 deletions(-)
create mode 100644
gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 89d1be6cea6..6ce12fce52e 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -630,6 +630,7 @@ static const struct attribute_spec mips_attribute_table[] =
{
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 }
};
@@ -1309,6 +1310,16 @@ 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 (const_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. */
@@ -1494,6 +1505,19 @@ mips_can_inline_p (tree caller, tree callee)
return default_target_can_inline_p (caller, callee);
}
+/* Implement TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P.
+
+ A function requesting 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)
+{
+ return !mips_use_hazard_barrier_return_p (decl);
+}
+
/* Handle an "interrupt" attribute with an optional argument. */
static tree
@@ -7921,6 +7945,11 @@ mips_function_ok_for_sibcall (tree decl, tree exp
ATTRIBUTE_UNUSED)
&& !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;
}
@@ -11008,6 +11037,17 @@ 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 returns require a MIPS32r2 processor or
greater");
+ else if (TARGET_MIPS16)
+ error ("hazard barrier returns are not supported for MIPS16 functions");
+ else
+ cfun->machine->use_hazard_barrier_return_p = true;
+ }
+
frame = &cfun->machine->frame;
memset (frame, 0, sizeof (*frame));
size = get_frame_size ();
@@ -12671,7 +12711,8 @@ 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. */
@@ -12712,6 +12753,11 @@ 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;
@@ -12770,6 +12816,11 @@ 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;
@@ -22777,10 +22828,9 @@ mips_asm_file_end (void)
#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
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index 47aac9d3d61..bae9ffe9b3c 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -3376,6 +3376,9 @@ 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
diff --git a/gcc/config/mips/mips.md b/gcc/config/mips/mips.md
index 455b9b802f6..dee71dc1fb0 100644
--- a/gcc/config/mips/mips.md
+++ b/gcc/config/mips/mips.md
@@ -159,6 +159,7 @@
;; The `.insn' pseudo-op.
UNSPEC_INSN_PSEUDO
+ UNSPEC_JRHB
])
(define_constants
@@ -6660,6 +6661,20 @@
[(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"
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 49df8e6dc38..8d2a0a23af6 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5540,6 +5540,12 @@ On MIPS targets, you can use the @code{nocompression}
function attribute
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
diff --git a/gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
b/gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
new file mode 100644
index 00000000000..3575af44dcd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/hazard-barrier-return-attribute.c
@@ -0,0 +1,20 @@
+/* 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 } } */
--
2.17.1
