[SH] Add support for tas.b instruction

[Oleg Endo <oleg dot endo at t-online dot de>]

Hello,

The attached patch adds support for the SH tas.b instruction by
introducing a new target option -menable-tas.
The patch was tested against rev 184589 with...

make info dvi pdf

make -k check RUNTESTFLAGS="--target_board=sh-sim\{
-m2/-ml,-m2/-mb, -m2a-single/-mb,
-m4-single/-ml,-m4-single/-mb,
-m4a-single/-ml,-m4a-single/-mb}"
	
make -k check RUNTESTFLAGS="--target_board=sh-sim\{
-m2/-ml/-msoft-atomic,-m2/-mb/-msoft-atomic,
-m2a-single/-mb/-msoft-atomic,
-m4-single/-ml/-msoft-atomic,-m4-single/-mb/-msoft-atomic,
-m4a-single/-ml/-msoft-atomic,-m4a-single/-mb/-msoft-atomic}"

make -k check RUNTESTFLAGS="--target_board=sh-sim\{
-m2/-ml/-msoft-atomic/-menable-tas,-m2/-mb/-msoft-atomic/-menable-tas,
-m2a-single/-mb/-msoft-atomic/-menable-tas,
-m4-single/-ml/-msoft-atomic/-menable-tas,
-m4-single/-mb/-msoft-atomic/-menable-tas,
-m4a-single/-ml/-msoft-atomic/-menable-tas,
-m4a-single/-mb/-msoft-atomic/-menable-tas}"

make -k check RUNTESTFLAGS="--target_board=sh-sim\{
-m2/-ml/-menable-tas,-m2/-mb/-menable-tas,
-m2a-single/-mb/-menable-tas,
-m4-single/-ml/-menable-tas,-m4-single/-mb/-menable-tas,
-m4a-single/-ml/-menable-tas,-m4a-single/-mb/-menable-tas}"

... and no new failures, except for the last test run which does not
enable any atomics.  There it fails the test case gcc.dg/atomic-flag.c.

This is because TARGET_ATOMIC_TEST_AND_SET_TRUEVAL is defined to 0x80,
but the code in optabs.c (expand_atomic_test_and_set) always uses
const1_rtx as the atomic flag true-value when expanding "single thread"
fake atomics.  However, the failing test case checks the written atomic
flag value against __GCC_ATOMIC_TEST_AND_SET_TRUEVAL, which is defined
in the SH target to 0x80.

One way to fix this problem is the example patch in my previous message
regarding this issue:
http://gcc.gnu.org/ml/gcc-patches/2012-02/msg01408.html

Another way would be to allow the TARGET_ATOMIC_TEST_AND_SET_TRUEVAL
hook to be evaluated (conditionally) at runtime.  Then for example, the
target could set it to 0x80 if atomics are enabled by the user, or leave
it at 0x01 if they aren't.

Other than that, OK for 4.8?

Cheers,
Oleg

2012-03-01  Oleg Endo  <olegendo@gcc.gnu.org>

	* config/sh/sh.h (TARGET_ATOMIC_TEST_AND_SET_TRUEVAL): New hook.
	* config/sh/sync.md (atomic_test_and_set): New expander.
	(tasb, atomic_test_and_set_soft): New insns.
	* config/sh/sh.opt (menable-tas): New option.
	* doc/invoke.texi (SH Options): Document it.


Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 184669)
+++ gcc/doc/invoke.texi	(working copy)
@@ -887,7 +887,8 @@
 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
 -maccumulate-outgoing-args -minvalid-symbols -msoft-atomic @gol
--mbranch-cost=@var{num} -mcbranchdi -mcmpeqdi -mfused-madd -mpretend-cmove}
+-mbranch-cost=@var{num} -mcbranchdi -mcmpeqdi -mfused-madd -mpretend-cmove @gol
+-menable-tas}
 
 @emph{Solaris 2 Options}
 @gccoptlist{-mimpure-text  -mno-impure-text @gol
@@ -17829,6 +17830,15 @@
 This option is enabled by default when the target is @code{sh-*-linux*}.
 For details on the atomic built-in functions see @ref{__atomic Builtins}.
 
+@item -menable-tas
+@opindex menable-tas
+Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}.
+Notice that depending on the particular hardware and software configuration
+this can degrade overall performance due to the operand cache line flushes
+that are implied by the @code{tas.b} instruction.  On multi-core SH4A
+processors the @code{tas.b} instruction must be used with caution since it
+can result in data corruption for certain cache configurations.
+
 @item -mspace
 @opindex mspace
 Optimize for space instead of speed.  Implied by @option{-Os}.
Index: gcc/config/sh/sh.h
===================================================================
--- gcc/config/sh/sh.h	(revision 184669)
+++ gcc/config/sh/sh.h	(working copy)
@@ -2475,4 +2475,11 @@
 /* FIXME: middle-end support for highpart optimizations is missing.  */
 #define high_life_started reload_in_progress
 
+/* The tas.b instruction sets the 7th bit in the byte, i.e. 0x80.
+   This value is used by optabs.c atomic op expansion code as well as in 
+   sync.md.  It must be defined as signed char here or else the movqi
+   pattern will refuse to load it as a QImode constant.  */
+#undef TARGET_ATOMIC_TEST_AND_SET_TRUEVAL
+#define TARGET_ATOMIC_TEST_AND_SET_TRUEVAL ((signed char)0x80)
+
 #endif /* ! GCC_SH_H */
Index: gcc/config/sh/sync.md
===================================================================
--- gcc/config/sh/sync.md	(revision 184669)
+++ gcc/config/sh/sync.md	(working copy)
@@ -365,3 +365,60 @@
 	 "1:	mov	r1,r15";
 }
   [(set_attr "length" "18")])
+
+(define_expand "atomic_test_and_set"
+  [(match_operand:SI 0 "register_operand" "")		;; bool result output
+   (match_operand:QI 1 "memory_operand" "")		;; memory
+   (match_operand:SI 2 "const_int_operand" "")]		;; model
+  "(TARGET_SOFT_ATOMIC || TARGET_ENABLE_TAS) && !TARGET_SHMEDIA"
+{
+  rtx addr = force_reg (Pmode, XEXP (operands[1], 0));
+
+  if (TARGET_ENABLE_TAS)
+    emit_insn (gen_tasb (addr));
+  else
+    {
+      rtx val = force_reg (QImode, 
+			   GEN_INT (TARGET_ATOMIC_TEST_AND_SET_TRUEVAL));
+      emit_insn (gen_atomic_test_and_set_soft (addr, val));
+    }
+
+  /* The result of the test op is the inverse of what we are
+     supposed to return.  Thus invert the T bit.  The inversion will be
+     potentially optimized away and integrated into surrounding code.  */
+  emit_insn (gen_movnegt (operands[0]));
+  DONE;
+})
+
+(define_insn "tasb"
+  [(set (reg:SI T_REG)
+	(eq:SI (mem:QI (match_operand:SI 0 "register_operand" "r"))
+	       (const_int 0)))
+   (set (mem:QI (match_dup 0))
+	(unspec:QI [(const_int 128)] UNSPEC_ATOMIC))]
+  "TARGET_ENABLE_TAS && !TARGET_SHMEDIA"
+  "tas.b	@%0"
+  [(set_attr "insn_class" "co_group")])
+
+(define_insn "atomic_test_and_set_soft"
+  [(set (reg:SI T_REG)
+	(eq:SI (mem:QI (match_operand:SI 0 "register_operand" "u"))
+	       (const_int 0)))
+   (set (mem:QI (match_dup 0))
+	(unspec:QI [(match_operand:QI 1 "register_operand" "u")] UNSPEC_ATOMIC))
+   (clobber (match_scratch:QI 2 "=&u"))
+   (clobber (reg:SI R0_REG))
+   (clobber (reg:SI R1_REG))]
+  "TARGET_SOFT_ATOMIC && !TARGET_ENABLE_TAS && !TARGET_SHMEDIA"
+{
+  return "mova	1f,r0"			"\n"
+	 "	.align 2"		"\n"
+	 "	mov	r15,r1"		"\n"
+	 "	mov	#(0f-1f),r15"	"\n"
+	 "0:	mov.b	@%0,%2"		"\n"
+	 "	mov.b	%1,@%0"		"\n"
+	 "1:	mov	r1,r15"		"\n"
+	 "	tst	%2,%2";
+}
+  [(set_attr "length" "16")])
+
Index: gcc/config/sh/sh.opt
===================================================================
--- gcc/config/sh/sh.opt	(revision 184669)
+++ gcc/config/sh/sh.opt	(working copy)
@@ -323,6 +323,10 @@
 Target Report Mask(SOFT_ATOMIC)
 Use software atomic sequences supported by kernel
 
+menable-tas
+Target Report RejectNegative Var(TARGET_ENABLE_TAS)
+Use tas.b instruction for __atomic_test_and_set
+
 mspace
 Target RejectNegative Alias(Os)
 Deprecated.  Use -Os instead