[RFC PATCH 1/2] RISC-V: __builtin_riscv_pause for all environment

[Tsukasa OI <research_trasio@irq.a4lg.com>]

From: Tsukasa OI <research_trasio@irq.a4lg.com>

The "pause" RISC-V hint instruction requires the 'Zihintpause' extension
(in the assembler).  However, GCC emits "pause" unconditionally, making
an assembler error while compiling code with __builtin_riscv_pause while
the 'Zihintpause' extension disabled.

However, the "pause" instruction code (0x0100000f) is a HINT and emitting
its instruction code is safe in any environment.

This commit implements handling for the 'Zihintpause' extension and emits
".insn 0x0100000f" instead of "pause" only if the extension is disabled
(making the diagnostics better).

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc
	(riscv_ext_version_table): Implement the 'Zihintpause' extension,
	version 2.0.  (riscv_ext_flag_table) Add 'Zihintpause' handling.
	* config/riscv/riscv-builtins.cc: Remove availability predicate
	"always" and add "hint_pause" and "hint_pause_pseudo", corresponding
	the existence of the 'Zihintpause' extension.
	(riscv_builtins) Split builtin implementation depending on the
	existence of the 'Zihintpause' extension.
	* config/riscv/riscv-opts.h
	(MASK_ZIHINTPAUSE, TARGET_ZIHINTPAUSE): New.
	* config/riscv/riscv.md (riscv_pause): Make it only available when
	the 'Zihintpause' extension is enabled.  (riscv_pause_insn) New
	"pause" implementation when the 'Zihintpause' extension is disabled.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/builtin_pause.c: Removed.
	* gcc.target/riscv/zihintpause.c:
	New test when the 'Zihintpause' extension is enabled.
	* gcc.target/riscv/zihintpause-noarch.c:
	New test when the 'Zihintpause' extension is disabled.
---
 gcc/common/config/riscv/riscv-common.cc             |  2 ++
 gcc/config/riscv/riscv-builtins.cc                  |  6 ++++--
 gcc/config/riscv/riscv-opts.h                       |  2 ++
 gcc/config/riscv/riscv.md                           |  7 ++++++-
 gcc/testsuite/gcc.target/riscv/builtin_pause.c      | 10 ----------
 gcc/testsuite/gcc.target/riscv/zihintpause-noarch.c | 11 +++++++++++
 gcc/testsuite/gcc.target/riscv/zihintpause.c        | 11 +++++++++++
 7 files changed, 36 insertions(+), 13 deletions(-)
 delete mode 100644 gcc/testsuite/gcc.target/riscv/builtin_pause.c
 create mode 100644 gcc/testsuite/gcc.target/riscv/zihintpause-noarch.c
 create mode 100644 gcc/testsuite/gcc.target/riscv/zihintpause.c

diff --git a/gcc/common/config/riscv/riscv-common.cc b/gcc/common/config/riscv/riscv-common.cc
index 2eb8c7cadff0..02502ba07e82 100644
--- a/gcc/common/config/riscv/riscv-common.cc
+++ b/gcc/common/config/riscv/riscv-common.cc
@@ -209,6 +209,7 @@ static const struct riscv_ext_version riscv_ext_version_table[] =
   {"zkt",   ISA_SPEC_CLASS_NONE, 1, 0},
 
   {"zihintntl", ISA_SPEC_CLASS_NONE, 1, 0},
+  {"zihintpause", ISA_SPEC_CLASS_NONE, 2, 0},
 
   {"zicboz",ISA_SPEC_CLASS_NONE, 1, 0},
   {"zicbom",ISA_SPEC_CLASS_NONE, 1, 0},
@@ -1344,6 +1345,7 @@ static const riscv_ext_flag_table_t riscv_ext_flag_table[] =
   {"zkt",    &gcc_options::x_riscv_zk_subext, MASK_ZKT},
 
   {"zihintntl", &gcc_options::x_riscv_zi_subext, MASK_ZIHINTNTL},
+  {"zihintpause", &gcc_options::x_riscv_zi_subext, MASK_ZIHINTPAUSE},
 
   {"zicboz", &gcc_options::x_riscv_zicmo_subext, MASK_ZICBOZ},
   {"zicbom", &gcc_options::x_riscv_zicmo_subext, MASK_ZICBOM},
diff --git a/gcc/config/riscv/riscv-builtins.cc b/gcc/config/riscv/riscv-builtins.cc
index 79681d759628..554fb7f69bb0 100644
--- a/gcc/config/riscv/riscv-builtins.cc
+++ b/gcc/config/riscv/riscv-builtins.cc
@@ -122,7 +122,8 @@ AVAIL (clmul_zbkc32_or_zbc32, (TARGET_ZBKC || TARGET_ZBC) && !TARGET_64BIT)
 AVAIL (clmul_zbkc64_or_zbc64, (TARGET_ZBKC || TARGET_ZBC) && TARGET_64BIT)
 AVAIL (clmulr_zbc32, TARGET_ZBC && !TARGET_64BIT)
 AVAIL (clmulr_zbc64, TARGET_ZBC && TARGET_64BIT)
-AVAIL (always,     (!0))
+AVAIL (hint_pause, TARGET_ZIHINTPAUSE)
+AVAIL (hint_pause_pseudo, !TARGET_ZIHINTPAUSE)
 
 /* Construct a riscv_builtin_description from the given arguments.
 
@@ -179,7 +180,8 @@ static const struct riscv_builtin_description riscv_builtins[] = {
 
   DIRECT_BUILTIN (frflags, RISCV_USI_FTYPE, hard_float),
   DIRECT_NO_TARGET_BUILTIN (fsflags, RISCV_VOID_FTYPE_USI, hard_float),
-  DIRECT_NO_TARGET_BUILTIN (pause, RISCV_VOID_FTYPE, always),
+  RISCV_BUILTIN (pause, "pause", RISCV_BUILTIN_DIRECT_NO_TARGET, RISCV_VOID_FTYPE, hint_pause),
+  RISCV_BUILTIN (pause_insn, "pause", RISCV_BUILTIN_DIRECT_NO_TARGET, RISCV_VOID_FTYPE, hint_pause_pseudo),
 };
 
 /* Index I is the function declaration for riscv_builtins[I], or null if the
diff --git a/gcc/config/riscv/riscv-opts.h b/gcc/config/riscv/riscv-opts.h
index 28d9b81bd800..a6c3e0c9098f 100644
--- a/gcc/config/riscv/riscv-opts.h
+++ b/gcc/config/riscv/riscv-opts.h
@@ -102,10 +102,12 @@ enum riscv_entity
 #define MASK_ZICSR    (1 << 0)
 #define MASK_ZIFENCEI (1 << 1)
 #define MASK_ZIHINTNTL (1 << 2)
+#define MASK_ZIHINTPAUSE (1 << 3)
 
 #define TARGET_ZICSR    ((riscv_zi_subext & MASK_ZICSR) != 0)
 #define TARGET_ZIFENCEI ((riscv_zi_subext & MASK_ZIFENCEI) != 0)
 #define TARGET_ZIHINTNTL ((riscv_zi_subext & MASK_ZIHINTNTL) != 0)
+#define TARGET_ZIHINTPAUSE ((riscv_zi_subext & MASK_ZIHINTPAUSE) != 0)
 
 #define MASK_ZAWRS   (1 << 0)
 #define TARGET_ZAWRS ((riscv_za_subext & MASK_ZAWRS) != 0)
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 688fd697255b..f2fcbfa6163b 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -2192,9 +2192,14 @@
 
 (define_insn "riscv_pause"
   [(unspec_volatile [(const_int 0)] UNSPECV_PAUSE)]
-  ""
+  "TARGET_ZIHINTPAUSE"
   "pause")
 
+(define_insn "riscv_pause_insn"
+  [(unspec_volatile [(const_int 0)] UNSPECV_PAUSE)]
+  ""
+  ".insn 0x0100000f")
+
 ;;
 ;;  ....................
 ;;
diff --git a/gcc/testsuite/gcc.target/riscv/builtin_pause.c b/gcc/testsuite/gcc.target/riscv/builtin_pause.c
deleted file mode 100644
index 9250937cabb9..000000000000
--- a/gcc/testsuite/gcc.target/riscv/builtin_pause.c
+++ /dev/null
@@ -1,10 +0,0 @@
-/* { dg-do compile } */
-/* { dg-options "-O2" }  */
-
-void test_pause()
-{
-  __builtin_riscv_pause ();
-}
-
-/* { dg-final { scan-assembler "pause" } } */
-
diff --git a/gcc/testsuite/gcc.target/riscv/zihintpause-noarch.c b/gcc/testsuite/gcc.target/riscv/zihintpause-noarch.c
new file mode 100644
index 000000000000..99ab953bd1db
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zihintpause-noarch.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64i -mabi=lp64"  { target { rv64 } } } */
+/* { dg-options "-march=rv32i -mabi=ilp32" { target { rv32 } } } */
+/* { dg-skip-if "" { *-*-* } { "-g" "-flto"} } */
+
+void test_pause()
+{
+  __builtin_riscv_pause ();
+}
+
+/* { dg-final { scan-assembler-times "0x0100000f" 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/zihintpause.c b/gcc/testsuite/gcc.target/riscv/zihintpause.c
new file mode 100644
index 000000000000..575b42277705
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zihintpause.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64i_zihintpause -mabi=lp64"  { target { rv64 } } } */
+/* { dg-options "-march=rv32i_zihintpause -mabi=ilp32" { target { rv32 } } } */
+/* { dg-skip-if "" { *-*-* } { "-g" "-flto"} } */
+
+void test_pause()
+{
+  __builtin_riscv_pause ();
+}
+
+/* { dg-final { scan-assembler-times "\tpause" 1 } } */
-- 
2.41.0