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* patch by J. Gareth Moreton: x86 CMP/TEST/Jcc optimisations, resolves #36624
git-svn-id: trunk@44029 -
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florian
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commit
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@ -3303,43 +3303,185 @@ unit aoptx86;
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function TX86AsmOptimizer.OptPass1Cmp(var p: tai): boolean;
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function TX86AsmOptimizer.OptPass1Cmp(var p: tai): boolean;
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var
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var
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v: TCGInt;
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v: TCGInt;
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hp1, hp2, hp3, hp4: tai;
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hp1, hp2: tai;
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begin
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begin
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Result:=false;
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Result:=false;
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{ cmp register,$8000 neg register
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je target --> jo target
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.... only if register is deallocated before jump.}
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if taicpu(p).oper[0]^.typ = top_const then
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case Taicpu(p).opsize of
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S_B: v:=$80;
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S_W: v:=$8000;
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S_L: v:=qword($80000000);
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{ actually, this will never happen: cmp with 64 bit constants is not possible }
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S_Q : v:=Int64($8000000000000000);
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else
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internalerror(2013112905);
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end;
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if MatchOpType(taicpu(p),Top_const,top_reg) and
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(taicpu(p).oper[0]^.val=v) and
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GetNextInstruction(p, hp1) and
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MatchInstruction(hp1,A_Jcc,[]) and
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(Taicpu(hp1).condition in [C_E,C_NE]) then
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begin
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begin
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TransferUsedRegs(TmpUsedRegs);
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{ Though GetNextInstruction can be factored out, it is an expensive
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UpdateUsedRegs(TmpUsedRegs,tai(p.next));
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call, so delay calling it until we have first checked cheaper
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if not(RegInUsedRegs(Taicpu(p).oper[1]^.reg, TmpUsedRegs)) then
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conditions that are independent of it. }
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if (taicpu(p).oper[0]^.val = 0) and
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(taicpu(p).oper[1]^.typ = top_reg) and
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GetNextInstruction(p, hp1) and
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MatchInstruction(hp1,A_Jcc,A_SETcc,[]) then
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begin
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begin
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DebugMsg(SPeepholeOptimization + 'CmpJe2NegJo done',p);
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hp2 := p;
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Taicpu(p).opcode:=A_NEG;
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{ When dealing with "cmp $0,%reg", only ZF and SF contain
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Taicpu(p).loadoper(0,Taicpu(p).oper[1]^);
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anything meaningful once it's converted to "test %reg,%reg";
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Taicpu(p).clearop(1);
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additionally, some jumps will always (or never) branch, so
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Taicpu(p).ops:=1;
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evaluate every jump immediately following the
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if Taicpu(hp1).condition=C_E then
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comparison, optimising the conditions if possible.
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Taicpu(hp1).condition:=C_O
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Similarly with SETcc... those that are always set to 0 or 1
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else
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are changed to MOV instructions }
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Taicpu(hp1).condition:=C_NO;
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while GetNextInstruction(hp2, hp1) and
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Result:=true;
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MatchInstruction(hp1,A_Jcc,A_SETcc,[]) do
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exit;
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begin
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case taicpu(hp1).condition of
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C_B, C_C, C_NAE, C_O:
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{ For B/NAE:
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Will never branch since an unsigned integer can never be below zero
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For C/O:
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Result cannot overflow because 0 is being subtracted
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}
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begin
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if taicpu(hp1).opcode = A_Jcc then
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begin
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DebugMsg(SPeepholeOptimization + 'Cmpcc2Testcc - condition B/C/NAE/O --> Never (jump removed)', hp1);
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TAsmLabel(taicpu(hp1).oper[0]^.ref^.symbol).decrefs;
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AsmL.Remove(hp1);
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hp1.Free;
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{ Since hp1 was deleted, hp2 must not be updated }
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Continue;
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end
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else
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begin
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DebugMsg(SPeepholeOptimization + 'Cmpcc2Testcc - condition B/C/NAE/O --> Never (set -> mov 0)', hp1);
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{ Convert "set(c) %reg" instruction to "movb 0,%reg" }
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taicpu(hp1).opcode := A_MOV;
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taicpu(hp1).condition := C_None;
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taicpu(hp1).opsize := S_B;
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taicpu(hp1).allocate_oper(2);
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taicpu(hp1).loadreg(1,taicpu(hp1).oper[0]^.reg);
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taicpu(hp1).loadconst(0, 0);
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end;
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end;
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C_BE, C_NA:
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begin
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{ Will only branch if equal to zero }
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DebugMsg(SPeepholeOptimization + 'Cmpcc2Testcc - condition BE/NA --> E', hp1);
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taicpu(hp1).condition := C_E;
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end;
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C_A, C_NBE:
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begin
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{ Will only branch if not equal to zero }
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DebugMsg(SPeepholeOptimization + 'Cmpcc2Testcc - condition A/NBE --> NE', hp1);
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taicpu(hp1).condition := C_NE;
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end;
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C_AE, C_NB, C_NC, C_NO:
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begin
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{ Will always branch }
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DebugMsg(SPeepholeOptimization + 'Cmpcc2Testcc - condition AE/NB/NC/NO --> Always', hp1);
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if taicpu(hp1).opcode = A_Jcc then
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begin
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MakeUnconditional(taicpu(hp1));
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{ Any jumps/set that follow will now be dead code }
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RemoveDeadCodeAfterJump(taicpu(hp1));
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Break;
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end
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else
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begin
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{ Convert "set(c) %reg" instruction to "movb 1,%reg" }
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taicpu(hp1).opcode := A_MOV;
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taicpu(hp1).condition := C_None;
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taicpu(hp1).opsize := S_B;
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taicpu(hp1).allocate_oper(2);
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taicpu(hp1).loadreg(1,taicpu(hp1).oper[0]^.reg);
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taicpu(hp1).loadconst(0, 1);
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end;
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end;
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C_None:
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InternalError(2020012201);
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C_P, C_PE, C_NP, C_PO:
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{ We can't handle parity checks and they should never be generated
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after a general-purpose CMP (it's used in some floating-point
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comparisons that don't use CMP) }
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InternalError(2020012202);
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else
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{ Zero/Equality, Sign, their complements and all of the
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signed comparisons do not need to be converted };
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end;
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hp2 := hp1;
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end;
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{ Convert the instruction to a TEST }
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taicpu(p).opcode := A_TEST;
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taicpu(p).loadreg(0,taicpu(p).oper[1]^.reg);
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Result := True;
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Exit;
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end
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else if (taicpu(p).oper[0]^.val = 1) and
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GetNextInstruction(p, hp1) and
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MatchInstruction(hp1,A_Jcc,A_SETcc,[]) and
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(taicpu(hp1).condition in [C_L, C_NGE]) then
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begin
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{ Convert; To:
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cmp $1,r/m cmp $0,r/m
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jl @lbl jle @lbl
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}
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DebugMsg(SPeepholeOptimization + 'Cmp1Jl2Cmp0Jle', p);
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taicpu(p).oper[0]^.val := 0;
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taicpu(hp1).condition := C_LE;
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{ If the instruction is now "cmp $0,%reg", convert it to a
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TEST (and effectively do the work of the "cmp $0,%reg" in
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the block above)
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If it's a reference, we can get away with not setting
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Result to True because he haven't evaluated the jump
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in this pass yet.
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}
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if (taicpu(p).oper[1]^.typ = top_reg) then
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begin
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taicpu(p).opcode := A_TEST;
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taicpu(p).loadreg(0,taicpu(p).oper[1]^.reg);
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Result := True;
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end;
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Exit;
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end
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else if (taicpu(p).oper[1]^.typ = top_reg) then
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begin
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{ cmp register,$8000 neg register
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je target --> jo target
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.... only if register is deallocated before jump.}
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case Taicpu(p).opsize of
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S_B: v:=$80;
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S_W: v:=$8000;
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S_L: v:=qword($80000000);
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{ S_Q will never happen: cmp with 64 bit constants is not possible }
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S_Q:
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Exit;
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else
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internalerror(2013112905);
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end;
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if (taicpu(p).oper[0]^.val=v) and
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GetNextInstruction(p, hp1) and
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MatchInstruction(hp1,A_Jcc,A_SETcc,[]) and
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(Taicpu(hp1).condition in [C_E,C_NE]) then
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begin
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TransferUsedRegs(TmpUsedRegs);
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UpdateUsedRegs(TmpUsedRegs,tai(p.next));
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if not(RegInUsedRegs(Taicpu(p).oper[1]^.reg, TmpUsedRegs)) then
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begin
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DebugMsg(SPeepholeOptimization + 'CmpJe2NegJo done',p);
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Taicpu(p).opcode:=A_NEG;
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Taicpu(p).loadoper(0,Taicpu(p).oper[1]^);
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Taicpu(p).clearop(1);
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Taicpu(p).ops:=1;
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if Taicpu(hp1).condition=C_E then
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Taicpu(hp1).condition:=C_O
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else
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Taicpu(hp1).condition:=C_NO;
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Result:=true;
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exit;
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end;
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end;
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end;
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end;
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end;
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end;
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end;
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end;
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