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+ MovMovMov2XChg optimization by J. Gareth Moreton

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git-svn-id: trunk@43858 -
This commit is contained in:
florian 2020-01-04 14:24:28 +00:00
parent 561ae7b6fb
commit 73c6cab096
1 changed files with 61 additions and 0 deletions
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61
compiler/x86/aoptx86.pas
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@ -3230,6 +3230,24 @@ unit aoptx86;
function TX86AsmOptimizer.OptPass2MOV(var p : tai) : boolean;
function IsXCHGAcceptable: Boolean; inline;
begin
{ Always accept if optimising for size }
Result := (cs_opt_size in current_settings.optimizerswitches) or
(
{$ifdef x86_64}
{ XCHG takes 3 cycles on AMD Athlon64 }
(current_settings.optimizecputype >= cpu_core_i)
{$else x86_64}
{ From the Pentium M onwards, XCHG only has a latency of 2 rather
than 3, so it becomes a saving compared to three MOVs with two of
them able to execute simultaneously. [Kit] }
(current_settings.optimizecputype >= cpu_PentiumM)
{$endif x86_64}
);
end;
var
hp1,hp2: tai;
{$ifdef x86_64}
@ -3310,6 +3328,49 @@ unit aoptx86;
exit;
end
else if MatchOpType(taicpu(p),top_reg,top_reg) and
IsXCHGAcceptable and
{ XCHG doesn't support 8-byte registers }
(taicpu(p).opsize <> S_B) and
MatchInstruction(hp1, A_MOV, []) and
MatchOpType(taicpu(hp1),top_reg,top_reg) and
(taicpu(hp1).oper[1]^.reg = taicpu(p).oper[0]^.reg) and
GetNextInstruction(hp1, hp2) and
MatchInstruction(hp2, A_MOV, []) and
{ Don't need to call MatchOpType for hp2 because the operand matches below cover for it }
MatchOperand(taicpu(hp2).oper[0]^, taicpu(p).oper[1]^.reg) and
MatchOperand(taicpu(hp2).oper[1]^, taicpu(hp1).oper[0]^.reg) then
begin
{ mov %reg1,%reg2
mov %reg3,%reg1 -> xchg %reg3,%reg1
mov %reg2,%reg3
(%reg2 not used afterwards)
Note that xchg takes 3 cycles to execute, and generally mov's take
only one cycle apiece, but the first two mov's can be executed in
parallel, only taking 2 cycles overall. Older processors should
therefore only optimise for size. [Kit]
}
TransferUsedRegs(TmpUsedRegs);
UpdateUsedRegs(TmpUsedRegs, tai(p.Next));
UpdateUsedRegs(TmpUsedRegs, tai(hp1.Next));
if not RegUsedAfterInstruction(taicpu(p).oper[1]^.reg, hp2, TmpUsedRegs) then
begin
DebugMsg(SPeepholeOptimization + 'MovMovMov2XChg', p);
AllocRegBetween(taicpu(hp2).oper[1]^.reg, p, hp1, UsedRegs);
taicpu(hp1).opcode := A_XCHG;
asml.Remove(p);
asml.Remove(hp2);
p.Free;
hp2.Free;
p := hp1;
Result := True;
Exit;
end;
end
else if MatchOpType(taicpu(p),top_reg,top_reg) and
{$ifdef x86_64}
MatchInstruction(hp1,[A_MOV,A_MOVZX,A_MOVSX,A_MOVSXD],[]) and
{$else x86_64}