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New backward MOV optimisation

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This commit is contained in:
J. Gareth "Curious Kit" Moreton 2022-01-05 17:41:32 +00:00
parent 33cf86ff9f
commit 15a5a62eb4
1 changed files with 51 additions and 2 deletions
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53
compiler/x86/aoptx86.pas
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@ -4155,8 +4155,8 @@ unit aoptx86;
movq x(ref),%reg64
shrq y,%reg64
To:
movq x+4(ref),%reg32
shrq y-32,%reg32 (Remove if y = 32)
movl x+4(ref),%reg32
shrl y-32,%reg32 (Remove if y = 32)
}
if (taicpu(p).opsize = S_Q) and
(taicpu(p).oper[0]^.typ = top_ref) and { Second operand will be a register }
@ -4198,6 +4198,55 @@ unit aoptx86;
Exit;
end;
{$endif x86_64}
{ Backward optimisation. If we have:
func. %reg1,%reg2
mov %reg2,%reg3
(dealloc %reg2)
Change to:
func. %reg1,%reg3 (see comment below for what a valid func. is)
}
if MatchOpType(taicpu(p), top_reg, top_reg) then
begin
CurrentReg := taicpu(p).oper[0]^.reg;
ActiveReg := taicpu(p).oper[1]^.reg;
TransferUsedRegs(TmpUsedRegs);
if not RegUsedAfterInstruction(CurrentReg, p, TmpUsedRegs) and
GetLastInstruction(p, hp2) and
(hp2.typ = ait_instruction) and
{ Have to make sure it's an instruction that only reads from
operand 1 and only writes (not reads or modifies) from operand 2;
in essence, a one-operand pure function such as BSR or POPCNT }
(taicpu(hp2).ops = 2) and
(insprop[taicpu(hp2).opcode].Ch * [Ch_Rop1, Ch_Wop2] = [Ch_Rop1, Ch_Wop2]) and
(taicpu(hp2).oper[1]^.typ = top_reg) and
(taicpu(hp2).oper[1]^.reg = CurrentReg) then
begin
case taicpu(hp2).opcode of
A_FSTSW, A_FNSTSW,
A_IN, A_INS, A_OUT, A_OUTS,
A_CMPS, A_LODS, A_MOVS, A_SCAS, A_STOS,
{ These routines have explicit operands, but they are restricted in
what they can be (e.g. IN and OUT can only read from AL, AX or
EAX. }
A_CMOVcc:
{ CMOV is not valid either because then CurrentReg will depend
on an unknown value if the condition is False and hence is
not a pure write }
;
else
begin
DebugMsg(SPeepholeOptimization + 'Removed MOV and changed destination on previous instruction to optimise register usage (FuncMov2Func)', p);
taicpu(hp2).oper[1]^.reg := ActiveReg;
AllocRegBetween(ActiveReg, hp2, p, TmpUsedRegs);
RemoveCurrentp(p, hp1);
Result := True;
Exit;
end;
end;
end;
end;
end;