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* x86: New OR->BTS peephole optimisation

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J. Gareth "Curious Kit" Moreton 2022-11-07 05:20:33 +00:00 committed by FPK
parent 314f632377
commit 827fe2bd83
1 changed files with 39 additions and 0 deletions
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39
compiler/x86/aoptx86.pas
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@ -14027,6 +14027,45 @@ unit aoptx86;
hp1,hp2 : tai;
begin
Result:=false;
{ If x is a power of 2 (popcnt = 1), change:
or $x, %reg/ref
To:
bts lb(x), %reg/ref
}
if (taicpu(p).opcode = A_OR) and
{$ifndef x86_64}
(
(cs_opt_size in current_settings.optimizerswitches) or
{ BTS takes more than 1 cycle on earlier processors }
(current_settings.optimizecputype >= cpu_Pentium2)
) and
{$endif not x86_64}
MatchOpType(taicpu(p), top_const, top_reg) and { "btx $x,mem" is unacceptably slow }
(PopCnt(QWord(taicpu(p).oper[0]^.val)) = 1) and
{ For sizes less than S_L, the byte size is equal or larger with BT,
so don't bother optimising }
(taicpu(p).opsize >= S_L) and
(
{ If the value can bit into an 8-bit signed integer, a smaller
instruction can be encded with OR, so don't optimise if it falls
within this range }
(taicpu(p).oper[0]^.val < -128) or
(taicpu(p).oper[0]^.val >= 127)
) and
(
{ Don't optimise if a test instruction follows }
not GetNextInstruction(p, hp1) or
not MatchInstruction(hp1, A_TEST, [taicpu(p).opsize])
) then
begin
DebugMsg(SPeepholeOptimization + 'Changed OR $0x' + hexstr(taicpu(p).oper[0]^.val, 2) + ' to BTS ' + debug_tostr(BsrQWord(taicpu(p).oper[0]^.val)) + ' to shrink instruction size (Or2Bts)', p);
taicpu(p).opcode := A_BTS;
taicpu(p).oper[0]^.val := BsrQWord(taicpu(p).oper[0]^.val); { Essentially the base 2 logarithm }
Result := True;
Exit;
end;
{ If x is a power of 2 (popcnt = 1), change:
test $x, %reg/ref
je / sete / cmove (or jne / setne)