On 7 September 2012 17:28, Richard Earnshaw <rearn...@arm.com> wrote: > > Ah, sigh! I'd forgotten about the cond-exec issue. That makes things > a little awkward, since we also have to deal with the fact that thumb1 > does not support predication. The solution, unfortunately, is thus a > bit more involved. > Sorry if your suggestion makes me ask a few more questions :-)
> What we need are two patterns (although currently it looks like we've got two, > in reality the predication means there are three), which need to read: What is the advantage of the version you propose? I mean there are already two explicit patterns, your proposal does not really bring factorization since we end up with two patterns. > (define_insn "*arm_revsh" > [(set (match_operand:SI 0 "s_register_operand" "=l,l,r") > (sign_extend:SI (bswap:HI (match_operand:HI 1 > "s_register_operand" "l,l,r"))))] > "arm_arch6" > "@ > revsh\t%0, %1 > revsh%?\t%0, %1 > revsh%?\t%0, %1" Why do we have to keep room for the predicate here? (%?) Doesn't this pattern match only in unconditional cases? BTW, I didn't manage to have GCC generate conditional revsh. I merely added an "if (y)" guard before calling builtin_bswap16, but this didn't turn into a conditional revsh. > [(set_attr "arch" "t1,t2,32") > (set_attr "length" "2,2,4")] > (define_insn "*arm_revsh_cond" > [(cond_exec (match_operator 2 "arm_comparison_operator" > [(match_operand 3 "cc_register" "") (const_int 0)]) > (set (match_operand:SI 0 "s_register_operand" "=l,r") > (sign_extend:SI (bswap:HI (match_operand:HI 1 > "s_register_operand" "l,r")))))] > "TARGET32_BIT && arm_arch6" > "revsh%?\t%0, %1" > [(set_attr "arch" "t2,*") > (set_attr "length" "2,4")]) > > Note that this removes the "predicable" attribute as we now handle this > manually rather than with the auto-generation. > > Sorry, this has turned out to be more complex than I originally realised. I understand that this is also applicable to the existing arm_rev and thumb1_rev patterns for 32 bit swaps. I'd like to understand the rationale & implications of your proposal. Thanks Christophe.
