[PATCH] xtensa: Improve indirect sibling call handling

[PATCH] xtensa: Improve indirect sibling call handling

[Takayuki 'January June' Suwa]

No longer needs the dedicated hard register (A11) for the address of the
call and the split patterns for fixups, due to the introduction of appropriate
register class and constraint.

(Note: "ISC_REGS" contains a hard register A8 used as a "static chain"
 pointer for nested functions, but no problem;  Pointer to nested function
 actually points to "trampoline", and trampoline itself doesn't receive
 "static chain" pointer to its parent's stack frame from the caller.)

gcc/ChangeLog:

	* config/xtensa/xtensa.h
	(enum reg_class, REG_CLASS_NAMES, REG_CLASS_CONTENTS):
	Add new register class "ISC_REGS".
	* config/xtensa/constraints.md (c): Add new register constraint.
	* config/xtensa/xtensa.md (define_constants): Remove "A11_REG".
	(sibcall_internal, sibcall_value_internal):
	Change to use the new register constraint, and remove two split
	patterns for fixups that are no longer needed.

gcc/testsuite/ChangeLog:

	* gcc.target/xtensa/sibcalls.c: Add a new test function to ensure
	that registers for arguments (occupy from A2 to A7) and for indirect
	sibcall (should be assigned to A8) neither conflict nor spill out.
---
 gcc/config/xtensa/constraints.md           |  5 ++++
 gcc/config/xtensa/xtensa.h                 |  3 +++
 gcc/config/xtensa/xtensa.md                | 29 ++--------------------
 gcc/testsuite/gcc.target/xtensa/sibcalls.c |  5 ++++
 4 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/gcc/config/xtensa/constraints.md b/gcc/config/xtensa/constraints.md
index 0b7dcd1440e..e4c314b267c 100644
--- a/gcc/config/xtensa/constraints.md
+++ b/gcc/config/xtensa/constraints.md
@@ -27,6 +27,11 @@
  "Boolean registers @code{b0}-@code{b15}; only available if the Xtensa
   Boolean Option is configured.")
 
+(define_register_constraint "c" "TARGET_WINDOWED_ABI ? NO_REGS : ISC_REGS"
+ "@internal
+  General-purpose AR registers for indirect sibling calls, @code{a2}-
+  @code{a8}.")
+
 (define_register_constraint "d" "TARGET_DENSITY ? AR_REGS: NO_REGS"
  "@internal
   All AR registers, including sp, but only if the Xtensa Code Density
diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
index d027a777227..d51658afa89 100644
--- a/gcc/config/xtensa/xtensa.h
+++ b/gcc/config/xtensa/xtensa.h
@@ -378,6 +378,7 @@ enum reg_class
   FP_REGS,			/* floating point registers */
   ACC_REG,			/* MAC16 accumulator */
   SP_REG,			/* sp register (aka a1) */
+  ISC_REGS,			/* registers for indirect sibling calls */
   RL_REGS,			/* preferred reload regs (not sp or fp) */
   GR_REGS,			/* integer registers except sp */
   AR_REGS,			/* all integer registers */
@@ -399,6 +400,7 @@ enum reg_class
   "FP_REGS",								\
   "ACC_REG",								\
   "SP_REG",								\
+  "ISC_REGS",								\
   "RL_REGS",								\
   "GR_REGS",								\
   "AR_REGS",								\
@@ -415,6 +417,7 @@ enum reg_class
   { 0xfff80000, 0x00000007 }, /* floating-point registers */ \
   { 0x00000000, 0x00000008 }, /* MAC16 accumulator */ \
   { 0x00000002, 0x00000000 }, /* stack pointer register */ \
+  { 0x000001fc, 0x00000000 }, /* registers for indirect sibling calls */ \
   { 0x0000fffd, 0x00000000 }, /* preferred reload registers */ \
   { 0x0000fffd, 0x00000000 }, /* general-purpose registers */ \
   { 0x0003ffff, 0x00000000 }, /* integer registers */ \
diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index 1294aab6c5d..3ed269249a4 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -25,7 +25,6 @@
   (A7_REG		7)
   (A8_REG		8)
   (A9_REG		9)
-  (A11_REG		11)
 
   (UNSPEC_NOP		2)
   (UNSPEC_PLT		3)
@@ -2279,7 +2278,7 @@
 })
 
 (define_insn "sibcall_internal"
-  [(call (mem:SI (match_operand:SI 0 "call_insn_operand" "nir"))
+  [(call (mem:SI (match_operand:SI 0 "call_insn_operand" "nic"))
 	 (match_operand 1 "" "i"))]
   "!TARGET_WINDOWED_ABI && SIBLING_CALL_P (insn)"
 {
@@ -2289,17 +2288,6 @@
    (set_attr "mode"	"none")
    (set_attr "length"	"3")])
 
-(define_split
-  [(call (mem:SI (match_operand:SI 0 "register_operand"))
-	 (match_operand 1 ""))]
-  "reload_completed
-   && !TARGET_WINDOWED_ABI && SIBLING_CALL_P (insn)
-   && ! call_used_or_fixed_reg_p (REGNO (operands[0]))"
-  [(set (reg:SI A11_REG)
-	(match_dup 0))
-   (call (mem:SI (reg:SI A11_REG))
-	 (match_dup 1))])
-
 (define_expand "sibcall_value"
   [(set (match_operand 0 "register_operand" "")
 	(call (match_operand 1 "memory_operand" "")
@@ -2311,7 +2299,7 @@
 
 (define_insn "sibcall_value_internal"
   [(set (match_operand 0 "register_operand" "=a")
-	(call (mem:SI (match_operand:SI 1 "call_insn_operand" "nir"))
+	(call (mem:SI (match_operand:SI 1 "call_insn_operand" "nic"))
 	      (match_operand 2 "" "i")))]
   "!TARGET_WINDOWED_ABI && SIBLING_CALL_P (insn)"
 {
@@ -2321,19 +2309,6 @@
    (set_attr "mode"	"none")
    (set_attr "length"	"3")])
 
-(define_split
-  [(set (match_operand 0 "register_operand")
-	(call (mem:SI (match_operand:SI 1 "register_operand"))
-	      (match_operand 2 "")))]
-  "reload_completed
-   && !TARGET_WINDOWED_ABI && SIBLING_CALL_P (insn)
-   && ! call_used_or_fixed_reg_p (REGNO (operands[1]))"
-  [(set (reg:SI A11_REG)
-	(match_dup 1))
-   (set (match_dup 0)
-	(call (mem:SI (reg:SI A11_REG))
-	      (match_dup 2)))])
-
 (define_insn "entry"
   [(set (reg:SI A1_REG)
 	(unspec_volatile:SI [(match_operand:SI 0 "const_int_operand" "i")]
diff --git a/gcc/testsuite/gcc.target/xtensa/sibcalls.c b/gcc/testsuite/gcc.target/xtensa/sibcalls.c
index d2b3fccf1e5..dff6750e209 100644
--- a/gcc/testsuite/gcc.target/xtensa/sibcalls.c
+++ b/gcc/testsuite/gcc.target/xtensa/sibcalls.c
@@ -17,4 +17,9 @@ int test_2(int (*a)(void)) {
     return a();
 }
 
+_Complex double test_3(_Complex double a, _Complex double (*b)(_Complex double, double)) {
+  bar(-1);
+  return b(a, 3.141592653589795);
+}
+
 /* { dg-final { scan-assembler-not "ret" } } */
-- 
2.20.1

Re: [PATCH] xtensa: Improve indirect sibling call handling

[Max Filippov]

On Thu, Aug 18, 2022 at 3:06 AM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> No longer needs the dedicated hard register (A11) for the address of the
> call and the split patterns for fixups, due to the introduction of appropriate
> register class and constraint.
>
> (Note: "ISC_REGS" contains a hard register A8 used as a "static chain"
>  pointer for nested functions, but no problem;  Pointer to nested function
>  actually points to "trampoline", and trampoline itself doesn't receive
>  "static chain" pointer to its parent's stack frame from the caller.)
>
> gcc/ChangeLog:
>
>         * config/xtensa/xtensa.h
>         (enum reg_class, REG_CLASS_NAMES, REG_CLASS_CONTENTS):
>         Add new register class "ISC_REGS".
>         * config/xtensa/constraints.md (c): Add new register constraint.
>         * config/xtensa/xtensa.md (define_constants): Remove "A11_REG".
>         (sibcall_internal, sibcall_value_internal):
>         Change to use the new register constraint, and remove two split
>         patterns for fixups that are no longer needed.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/xtensa/sibcalls.c: Add a new test function to ensure
>         that registers for arguments (occupy from A2 to A7) and for indirect
>         sibcall (should be assigned to A8) neither conflict nor spill out.
> ---
>  gcc/config/xtensa/constraints.md           |  5 ++++
>  gcc/config/xtensa/xtensa.h                 |  3 +++
>  gcc/config/xtensa/xtensa.md                | 29 ++--------------------
>  gcc/testsuite/gcc.target/xtensa/sibcalls.c |  5 ++++
>  4 files changed, 15 insertions(+), 27 deletions(-)

Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.

-- 
Thanks.
-- Max