Sintendo
17dc870847
More efficient code can be generated if the shift amount is known at compile time. Similar optimizations were present in JitArm64 already, but were missing in Jit64. - By using an 8-bit immediate we can eliminate the need for ECX as a scratch register, thereby reducing register pressure and occasionally eliminating a spill. Before: B9 18 00 00 00 mov ecx,18h 41 8B F7 mov esi,r15d 48 D3 E6 shl rsi,cl 8B F6 mov esi,esi After: 41 8B CF mov ecx,r15d C1 E1 18 shl ecx,18h - PowerPC has strange shift amount masking behavior which is emulated using 64-bit shifts, even though we only care about a 32-bit result. If the shift amount is known, we can handle this special case separately, and use 32-bit shift instructions otherwise. We also no longer need to clear the upper 32 bits of the register. Before: BE F8 FF FF FF mov esi,0FFFFFFF8h 8B CE mov ecx,esi 41 8B F4 mov esi,r12d 48 D3 E6 shl rsi,cl 8B F6 mov esi,esi After: Nothing, register is set to constant zero. - A shift by zero becomes a simple MOV. Before: BE 00 00 00 00 mov esi,0 8B CE mov ecx,esi 41 8B F3 mov esi,r11d 48 D3 E6 shl rsi,cl 8B F6 mov esi,esi After: 41 8B FB mov edi,r11d