Hello,
I use (define_subst ...) in a way that solves my .md factoring problems but I
wonder if this use is expected and if will be maintained / documented in the
future.
Target is a 64-bit core whose GPRs are 64-bit wide, but it also has 32-bit
integer arithmetic instructions that clear the 32 upper bits of the destination
register.
For each instruction template, e.g. "addsi3", I define another one that
zero-extends the result to 64 bits from 32 bits.
Before using (define_subst ...), that was:
(define_insn "addsi3"
[(set (match_operand:SI 0 "register_operand" "=r,r,r")
(plus:SI (match_operand:SI 1 "register_operand" "r,r,r")
(match_operand:SI 2 "register_w32_operand" "r,I10,W32")))]
""
"addw %0 = %1, %2"
[(set_attr "type" "alu_tiny,alu_tiny_w,alu_tiny_x")
(set_attr "length" "4,4,8")]
)
;; zero-extend version of addsi3
(define_insn "*addsi3_zext"
[(set (match_operand:DI 0 "register_operand" "=r,r,r")
(zero_extend:DI (plus:SI (match_operand:SI 1 "register_operand"
"r,r,r")
(match_operand:SI 2 "register_w32_operand"
"r,I10,W32")))]
""
"addw %0 = %1, %2"
[(set_attr "type" "alu_tiny,alu_tiny_w,alu_tiny_x")
(set_attr "length" "4,4,8")]
)
The issue is to transform (set (match_operand:SI 0 ...)) to (set
(match_operand:DI 0 ...)), that is, change SI mode to DI mode.
However, using (match_dup 0) in the (define_subst ...) output-template expands
to (set (match_operand:SI 0 ...)), that is, not DI mode.
So I wrote the (define_subst ...) to force DI mode as follows:
(define_subst "arith_zx_subst"
[(set (match_operand:SI 0 "" "")
(match_operand:SI 1 "" ""))]
""
[(set (match_operand:DI 0 "register_operand" "=r")
(zero_extend:DI (match_dup 1)))]
)
(define_insn "addsi3<arith_zx>"
[(set (match_operand:SI 0 "register_operand" "=r,r,r")
(plus:SI (match_operand:SI 1 "register_operand" "r,r,r")
(match_operand:SI 2 "register_w32_operand" "r,I10,W32")))]
""
"addw %0 = %1, %2"
[(set_attr "type" "alu_tiny,alu_tiny_w,alu_tiny_x")
(set_attr "length" "4,4,8")]
)
That is, the output-template of (define_subst ...) uses (match_operand ...) to
force the DI mode, and does not use (match_dup ..) as explained in the
Internals.
Is that the rigth way to do it?
Then, by looking at the mddump, I noticed a seemingly strange value for the
attribute generated by the (define_subst ...) expansion:
;; ../../gcc/config/kvx/scalar.md: 1044
(define_insn ("addsi3")
[
(set (match_operand:SI 0 ("register_operand") ("=r,r,r"))
(plus:SI (match_operand:SI 1 ("register_operand") ("r,r,r"))
(match_operand:SI 2 ("register_w32_operand") ("r,I10,W32"))))
] ("") ("addw %0 = %1, %2")
[
(set_attr ("type") ("alu_tiny,alu_tiny_w,alu_tiny_x"))
(set_attr ("length") ("4,4,8"))
])
;; ../../gcc/config/kvx/scalar.md: 1044
(define_insn ("addsi3_zx")
[
(set (match_operand:DI 0 ("register_operand") ("=r,r,r"))
(zero_extend:DI (plus:SI (match_operand:SI 1 ("register_operand")
("r,r,r"))
(match_operand:SI 2 ("register_w32_operand")
("r,I10,W32")))))
] ("") ("addw %0 = %1, %2")
[
(set_attr ("type") ("alu_tiny,alu_tiny_w,alu_tiny_x"))
(set_attr ("length") ("4,4,8"))
(set_attr ("arith_zx_subst") ("no"))
])
Precisely, attribute "arith_zx_subst" is set to "no", whereas it has been
declared by GCC in the mddump as:
;; ../../gcc/config/kvx/scalar.md: 1035
(define_attr ("arith_zx_subst") ("no,yes")
(const_string ("no")))
Is there a way for "arith_zx_subst" to have the "yes" value in the templates
generated by (define_subst ...)?
Finally, to have both a template for zero_extend:DI and a template for
sign_extend:DI to be generated from the original SI template, I have applied a
double (define_subst ...) to the original "addsi3" template as follows:
(define_subst_attr "arith_zx" "arith_zx_subst" "" "_zx")
(define_subst "arith_zx_subst"
[(set (match_operand:SI 0 "" "")
(match_operand:SI 1 "" ""))]
""
[(set (match_operand:DI 0 "register_operand" "=r")
(zero_extend:DI (match_dup 1)))]
)
(define_subst_attr "arith_sx" "arith_sx_subst" "" "_sx")
(define_subst_attr "modif_sx" "arith_sx_subst" "" ".sx")
(define_subst "arith_sx_subst"
[(set (match_operand:SI 0 "" "")
(match_operand:SI 1 "" ""))]
""
[(set (match_operand:DI 0 "register_operand" "=r")
(sign_extend:DI (match_dup 1)))]
)
(define_insn "addsi3<arith_zx><arith_sx>"
[(set (match_operand:SI 0 "register_operand" "=r,r,r")
(plus:SI (match_operand:SI 1 "register_operand" "r,r,r")
(match_operand:SI 2 "register_w32_operand" "r,I10,W32")))]
""
"addw<modif_sx> %0 = %1, %2"
[(set_attr "type" "alu_tiny,alu_tiny_w,alu_tiny_x")
(set_attr "length" "4,4,8")]
)
While this produces the expected insn templates "addsi3", "addsi3_zx",
"addsi3_sx", is this use of multiple (define_subst ...) is anticipated or
correct?
I have tried before combining a single (define_subst ...) with a code iterator
ANY_EXTEND inside the output-template of (define_subst ...) to iterate
zero_extend and sign_extend, but this did not work, as ANY_EXTEND was just
replaced by the first in its list of operators.
Benoît Dinechin
CTO XPU Kalray
