Hi :
I am studying multiplication-accumulate patterns for mips
and noticed there are some changes when IRA was merged.
There are two pattern which confused me, as :
1: In pattern "*mul_acc_si", there's constraint like "*?*?".
what does this supposed to do?
I could not connect "*?" with docu
On 03/15/2010 01:00 AM, Amker.Cheng wrote:
1: In pattern "*mul_acc_si", there's constraint like "*?*?".
what does this supposed to do?
'*' is in the Constraint Modifier Characters section of the docs. It
means ignore the next character for register class preferencing. '?' is
in the Multipl
> If you don't know anything about register class preferencing or reload as
> yet, then this is probably not going to make much sense to you, but it isn't
> anything important you need to worry about at this point. It is a very
> minor performance optimization.
>
It makes sense to me now, though I
On Tue, 2010-03-16 at 15:12 +0800, Amker.Cheng wrote:
> In my understanding, the macro GENERATE_MADD_MSUB is true when the processor
> has
> madd insn, rather than madd2. And the macro "ISA_HAS_MUL3" is false if it
> has
> no mul insn.
>
> for this kind processor, gcc will
> step 1 : generate in
> The reasoning here is
> that if splitting will result in worse code, then we shouldn't have
> accepted it in the first place. If dropping this alternative results in
> register allocator failures for some strange reason, then we accept it
> and generate the 3 instruction sequence with a new defi
On Thu, 2010-03-18 at 19:20 +0800, Amker.Cheng wrote:
> Does it possible that the method would ever result in register
> allocator failure?
> In my understanding, doesn't reload pass would do whatever it can to make
> all insns' constraints satisfied?
In theory, there should be no failure. In pra
