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* x86: PostPeepholeOptMov attempts to convert mov $0,%reg to

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xor %reg,%reg and mov $-1,%reg to or $-1,%reg under
	 -Os even if the flags are in use by looking ahead.
This commit is contained in:
J. Gareth "Curious Kit" Moreton 2023-11-10 19:40:14 +00:00 committed by FPK
parent 63879e74cd
commit 1f178d381f
1 changed files with 15 additions and 2 deletions
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17
compiler/x86/aoptx86.pas
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@ -15249,6 +15249,7 @@ unit aoptx86;
function TX86AsmOptimizer.PostPeepholeOptMov(var p : tai) : Boolean;
var
Value, RegName: string;
hp1: tai;
begin
Result:=false;
if (taicpu(p).oper[1]^.typ = top_reg) and (taicpu(p).oper[0]^.typ = top_const) then
@ -15257,7 +15258,12 @@ unit aoptx86;
case taicpu(p).oper[0]^.val of
0:
{ Don't make this optimisation if the CPU flags are required, since XOR scrambles them }
if not (RegInUsedRegs(NR_DEFAULTFLAGS,UsedRegs)) then
if not RegInUsedRegs(NR_DEFAULTFLAGS,UsedRegs) or
(
{ See if we can still convert the instruction }
GetNextInstructionUsingReg(p, hp1, NR_DEFAULTFLAGS) and
RegLoadedWithNewValue(NR_DEFAULTFLAGS, hp1)
) then
begin
{ change "mov $0,%reg" into "xor %reg,%reg" }
taicpu(p).opcode := A_XOR;
@ -15302,7 +15308,14 @@ unit aoptx86;
{ Don't make this optimisation if the CPU flags are required, since OR scrambles them }
if (cs_opt_size in current_settings.optimizerswitches) and
(taicpu(p).opsize <> S_B) and
not (RegInUsedRegs(NR_DEFAULTFLAGS,UsedRegs)) then
(
not RegInUsedRegs(NR_DEFAULTFLAGS,UsedRegs) or
(
{ See if we can still convert the instruction }
GetNextInstructionUsingReg(p, hp1, NR_DEFAULTFLAGS) and
RegLoadedWithNewValue(NR_DEFAULTFLAGS, hp1)
)
) then
begin
{ change "mov $-1,%reg" into "or $-1,%reg" }
{ NOTES: