On 04/26/10 22:09, Ian Lance Taylor wrote:
Greg McGary<g...@mcgary.org> writes:
I have a port without div or mod machine instructions. I wrote
divmodsi4 patterns that do the libcall directly, hoping that GCC would
recognize the opportunity to use a single divmodsi4 to compute both
quotient and remainder. Alas, GCC calls divmodsi4 twice with the same
divisor and dividend operands. Is this supposed to work? Is there a
special trick to help the optimizer recognize the redundant insn? I
saw the 4yr-old thread regarding picochip's desire for the same effect
and followed the same approach implemented in the current picochip.md
(as well as my own approach) but no luck.
Using a divmodsi4 insn instead of divsi3/modsi3 insns ought to work.
You may need to give more information, such as the test case you are
using, and what your divmodsi4 insn looks like.
Ian
The test case is __udivmoddi4 from libgcc2.c, specifically
the macro __udiv_qrnnd_c from longlong.h, which does this:
__r1 = (n1) % __d1;
__q1 = (n1) / __d1;
... and this ...
__r0 = __r1 % __d1;
__q0 = __r1 / __d1;
Below is my original insn set. The __udivmodsi4 libcall accepts
operands in r1/r2, then returns quotient in r4 and remainder in r1
(define_insn_and_split "udivmodsi4"
[(set (match_operand:SI 0 "gen_reg_operand" "=r")
(udiv:SI (match_operand:SI 1 "gen_reg_operand" "r")
(match_operand:SI 2 "gen_reg_operand" "r")))
(set (match_operand:SI 3 "gen_reg_operand" "=r")
(umod:SI (match_dup 1)
(match_dup 2)))
(clobber (reg:SI 1))
(clobber (reg:SI 2))
(clobber (reg:SI 3))
(clobber (reg:SI 4))
(clobber (reg:CC CC_REGNUM))
(clobber (reg:SI RETURN_POINTER_REGNUM))]
""
"#"
"reload_completed"
[(set (reg:SI 1)
(match_dup 1))
(set (reg:SI 2)
(match_dup 2))
(parallel [(set (reg:SI 4)
(udiv:SI (reg:SI 1)
(reg:SI 2)))
(set (reg:SI 1)
(umod:SI (reg:SI 1)
(reg:SI 2)))
(clobber (reg:SI 2))
(clobber (reg:SI 3))
(clobber (reg:CC CC_REGNUM))
(clobber (reg:SI RETURN_POINTER_REGNUM))])
(set (match_dup 0)
(reg:SI 4))
(set (match_dup 3)
(reg:SI 1))])
(define_insn "*udivmodsi4_libcall"
[(set (reg:SI 4)
(udiv:SI (reg:SI 1)
(reg:SI 2)))
(set (reg:SI 1)
(umod:SI (reg:SI 1)
(reg:SI 2)))
(clobber (reg:SI 2))
(clobber (reg:SI 3))
(clobber (reg:CC CC_REGNUM))
(clobber (reg:SI RETURN_POINTER_REGNUM))]
""
"call\\t__udivmodsi4"
[(set_attr "length" "4")])
Here is an alternative patterned after the approach in picochip.md. I
had hoped since the picochip guys reported the same trouble four years
ago, the current picochip.md might have the magic bits.
(define_expand "udivmodsi4"
[(parallel [(set (reg:SI 1)
(match_operand:SI 1 "gen_reg_operand" "r"))
(clobber (reg:CC CC_REGNUM))])
(parallel [(set (reg:SI 2)
(match_operand:SI 2 "gen_reg_operand" "r"))
(clobber (reg:CC CC_REGNUM))])
(parallel [(unspec_volatile [(const_int 0)] UNSPEC_UDIVMOD)
(set (reg:SI 4)
(udiv:SI (reg:SI 1)
(reg:SI 2)))
(set (reg:SI 1)
(umod:SI (reg:SI 1)
(reg:SI 2)))
(clobber (reg:SI 2))
(clobber (reg:SI 3))
(clobber (reg:CC CC_REGNUM))
(clobber (reg:SI RETURN_POINTER_REGNUM))])
(set (match_operand:SI 0 "gen_reg_operand" "=r")
(reg:SI 4))
(set (match_operand:SI 3 "gen_reg_operand" "=r")
(reg:SI 1))])
(define_insn "*udivmodsi4_libcall"
[(unspec_volatile [(const_int 0)] UNSPEC_UDIVMOD)
(set (reg:SI 4)
(udiv:SI (reg:SI 1)
(reg:SI 2)))
(set (reg:SI 1)
(umod:SI (reg:SI 1)
(reg:SI 2)))
(clobber (reg:SI 2))
(clobber (reg:SI 3))
(clobber (reg:CC CC_REGNUM))
(clobber (reg:SI RETURN_POINTER_REGNUM))]
""
"call\\t__udivmodsi4"
[(set_attr "length" "4")])
Alas, neither of them eliminates the redundant libcall. If no clues
are forthcoming, I'll begin debugging CSE.
G
