Jit64: subfx - Optimize more constant a cases

Consider the case where d and a refer to the same PowerPC register,
which is known to hold an immediate value by the RegCache. We place a
ReadWrite constraint on this register and bind it to an x86 register.
The RegCache then allocates a new register, initializes it with the
immediate, and returns a RCX64Reg for both d and a.

At this point information about the immediate value becomes unreachable.
In the case of subfx, this generates suboptimal code:

Before 1:
BF 1E 00 00 00       mov         edi,1Eh       <- done by RegCache
8B C7                mov         eax,edi
8B FE                mov         edi,esi
2B F8                sub         edi,eax

Before 2:
BE 00 AC 3F 80       mov         esi,803FAC00h <- done by RegCache
8B C6                mov         eax,esi
8B 75 EC             mov         esi,dword ptr [rbp-14h]
2B F0                sub         esi,eax

The solution is to explicitly handle the constant a case before having
the RegCache allocate registers for us.

After 1:
8D 7E E2             lea         edi,[rsi-1Eh]

After 2:
8B 75 EC             mov         esi,dword ptr [rbp-14h]
81 EE 00 AC 3F 80    sub         esi,803FAC00h

0 files changed, 0 insertions, 0 deletions