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x86: new optimisation to change add/sub 128,(dest) to sub/add -128,(dest) to reduce binary size

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J. Gareth "Curious Kit" Moreton 2021-11-13 00:19:15 +00:00 committed by FPK
parent e994bacbba
commit 9f60628e5b
1 changed files with 34 additions and 2 deletions
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36
compiler/x86/aoptx86.pas
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@ -10640,7 +10640,41 @@ unit aoptx86;
function TX86AsmOptimizer.PostPeepholeOptADDSUB(var p : tai) : boolean;
var
hp1, hp2: tai;
Opposite: TAsmOp;
begin
Result := False;
{ Change:
add/sub 128,(dest)
To:
sub/add -128,(dest)
This generaally takes fewer bytes to encode because -128 can be stored
in a signed byte, whereas +128 cannot.
}
if (taicpu(p).opsize <> S_B) and MatchOperand(taicpu(p).oper[0]^, 128) then
begin
if taicpu(p).opcode = A_ADD then
Opposite := A_SUB
else
Opposite := A_ADD;
DebugMsg(SPeepholeOptimization + debug_op2str(taicpu(p).opcode) + ' 128,' + debug_operstr(taicpu(p).oper[1]^) + ' changed to ' +
debug_op2str(opposite) + ' -128,' + debug_operstr(taicpu(p).oper[1]^) + ' to reduce instruction size', p);
taicpu(p).opcode := Opposite;
taicpu(p).oper[0]^.val := -128;
{ No further optimisations can be made on this instruction, so move
onto the next one to save time }
p := tai(p.Next);
UpdateUsedRegs(p);
Result := True;
Exit;
end;
{ Detect:
add/sub %reg2,(dest)
add/sub x, (dest)
@ -10651,8 +10685,6 @@ unit aoptx86;
"Add swap" and "Sub swap" optimisations done in pass 1 if no new
optimisations could be made.
}
Result := False;
if (taicpu(p).oper[0]^.typ = top_reg) and
not RegInOp(taicpu(p).oper[0]^.reg, taicpu(p).oper[1]^) and
(