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* Patch by J. Gareth "Kit" Moreton (issue #39343). x86 peephole

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optimization of conditions which are always true or false.
This commit is contained in:
Yuriy Sydorov 2021-09-07 20:09:47 +03:00
parent 940ac567a5
commit 6007ceb908
1 changed files with 115 additions and 1 deletions
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116
compiler/x86/aoptx86.pas
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@ -2194,6 +2194,7 @@ unit aoptx86;
function TX86AsmOptimizer.OptPass1MOV(var p : tai) : boolean;
var
hp1, hp2, hp3: tai;
DoOptimisation, TempBool: Boolean;
procedure convert_mov_value(signed_movop: tasmop; max_value: tcgint); inline;
begin
@ -2622,7 +2623,120 @@ unit aoptx86;
}
TransferUsedRegs(TmpUsedRegs);
UpdateUsedRegs(TmpUsedRegs, tai(p.Next));
if not (RegInUsedRegs(NR_DEFAULTFLAGS, TmpUsedRegs)) then
DoOptimisation := True;
{ Even if the flags are used, we might be able to do the optimisation
if the conditions are predictable }
if RegInUsedRegs(NR_DEFAULTFLAGS, TmpUsedRegs) then
begin
{ Only perform if ### = %reg (the same register) or equal to 0,
so %reg is guaranteed to still have a value of zero }
if MatchOperand(taicpu(hp1).oper[0]^, 0) or
MatchOperand(taicpu(hp1).oper[0]^, taicpu(hp1).oper[1]^.reg) then
begin
hp2 := hp1;
UpdateUsedRegs(TmpUsedRegs, tai(hp1.Next));
while RegInUsedRegs(NR_DEFAULTFLAGS, TmpUsedRegs) and
GetNextInstruction(hp2, hp3) do
begin
{ Don't continue modifying if the flags state is getting changed }
if RegModifiedByInstruction(NR_DEFAULTFLAGS, hp3) then
Break;
UpdateUsedRegs(TmpUsedRegs, tai(hp3.Next));
if MatchInstruction(hp3, A_Jcc, A_SETcc, A_CMOVcc, []) then
begin
if condition_in(C_E, taicpu(hp3).condition) or (taicpu(hp3).condition in [C_NC, C_NS, C_NO]) then
begin
{ Condition is always true }
case taicpu(hp3).opcode of
A_Jcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always true (jump made unconditional)', hp3);
{ Check for jump shortcuts before we destroy the condition }
DoJumpOptimizations(hp3, TempBool);
MakeUnconditional(taicpu(hp3));
Result := True;
end;
A_CMOVcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always true (CMOVcc -> MOV)', hp3);
taicpu(hp3).opcode := A_MOV;
taicpu(hp3).condition := C_None;
Result := True;
end;
A_SETcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always true (changed to MOV 1)', hp3);
{ Convert "set(c) %reg" instruction to "movb 1,%reg" }
taicpu(hp3).opcode := A_MOV;
taicpu(hp3).ops := 2;
taicpu(hp3).condition := C_None;
taicpu(hp3).opsize := S_B;
taicpu(hp3).loadreg(1,taicpu(hp3).oper[0]^.reg);
taicpu(hp3).loadconst(0, 1);
Result := True;
end;
else
InternalError(2021090701);
end;
end
else if (taicpu(hp3).condition in [C_A, C_B, C_C, C_G, C_L, C_NE, C_NZ, C_O, C_S]) then
begin
{ Condition is always false }
case taicpu(hp3).opcode of
A_Jcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always false (jump removed)', hp3);
TAsmLabel(taicpu(hp3).oper[0]^.ref^.symbol).decrefs;
RemoveInstruction(hp3);
Result := True;
{ Since hp3 was deleted, hp2 must not be updated }
Continue;
end;
A_CMOVcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always false (conditional load removed)', hp3);
RemoveInstruction(hp3);
Result := True;
{ Since hp3 was deleted, hp2 must not be updated }
Continue;
end;
A_SETcc:
begin
DebugMsg(SPeepholeOptimization + 'Condition is always false (changed to MOV 0)', hp3);
{ Convert "set(c) %reg" instruction to "movb 0,%reg" }
taicpu(hp3).opcode := A_MOV;
taicpu(hp3).ops := 2;
taicpu(hp3).condition := C_None;
taicpu(hp3).opsize := S_B;
taicpu(hp3).loadreg(1,taicpu(hp3).oper[0]^.reg);
taicpu(hp3).loadconst(0, 0);
Result := True;
end;
else
InternalError(2021090702);
end;
end
else
{ Uncertain what to do - don't optimise (although optimise other conditional statements if present) }
DoOptimisation := False;
end;
hp2 := hp3;
end;
{ Flags are still in use - don't optimise }
if DoOptimisation and RegInUsedRegs(NR_DEFAULTFLAGS, TmpUsedRegs) then
DoOptimisation := False;
end
else
DoOptimisation := False;
end;
if DoOptimisation then
begin
{$ifdef x86_64}
{ OR only supports 32-bit sign-extended constants for 64-bit