On 2020-02-07 16:44, Segher Boessenkool wrote:
Hi!
On Fri, Feb 07, 2020 at 03:41:25PM +0100, m wrote:
...so I tried to write a corresponding matching pattern, like so:
(define_insn "smulhshi3"
[(set (match_operand:HI 0 "register_operand" "=r")
(truncate:HI
(ashiftrt:SI
(mult:SI
(sign_extend:SI (match_operand:HI 1
"register_operand" "r"))
(sign_extend:SI (match_operand:HI 2
"register_operand" "r")))
(const_int 15))))]
"TARGET_PACKED_OPS"
"mulq.h\\t%0, %1, %2")
However, I am unable to trigger this code path. I have tried with the
following C code:
short mulq(short op1, short op2) {
return (short) (((int) op1 * (int) op2) >> (32 / 2 - 1));
}
But I just get the regular 4-instruction result (2x sign extend, 1x mul,
1x shift).
What does -fdump-rtl-combine-all show it tried? *Did* it try anything?
Segher
Cool option. I'm not really sure how to read the output tough. The
closest it seems to try to match is this:
Failed to match this instruction:
(set (reg:SI 85)
(ashiftrt:SI (mult:SI (sign_extend:SI (subreg:HI (reg:SI 86) 0))
(reg:SI 83 [ op2D.1381 ]))
(const_int 15 [0xf])))
It seems that it has already decided to split the instruction into
several operations (the truncate operation is not there, and the second
sign_extend:SI (subreg:HI ...) is also missing).
/Marcus
