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* x86: New Op/TEST optimisation that rearranges register usage for the most efficient execution

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J. Gareth "Curious Kit" Moreton 2024-03-11 08:54:57 +00:00 committed by FPK
parent 7c609ee7c4
commit 948766a37a
1 changed files with 73 additions and 1 deletions
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74
compiler/x86/aoptx86.pas
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@ -12506,10 +12506,82 @@ unit aoptx86;
function TX86AsmOptimizer.OptPass2Test(var p: tai): Boolean;
var
hp1, hp2, pCond: tai;
SourceReg, TargetReg: TRegister;
begin
Result := False;
{ Search ahead for CMOV instructions }
{ In some situations, we end up with an inefficient arrangement of
instructions in the form of:
or %reg1,%reg2
(%reg1 deallocated)
test %reg2,%reg2
mov x,%reg2
we may be able to swap and rearrange the registers to produce:
or %reg2,%reg1
mov x,%reg2
test %reg1,%reg1
(%reg1 deallocated)
}
if (cs_opt_level3 in current_settings.optimizerswitches) and
(taicpu(p).oper[1]^.typ = top_reg) and
(
MatchOperand(taicpu(p).oper[0]^, taicpu(p).oper[1]^.reg) or
MatchOperand(taicpu(p).oper[0]^, -1)
) and
GetNextInstruction(p, hp1) and
MatchInstruction(hp1, A_MOV, []) and
(taicpu(hp1).oper[1]^.typ = top_reg) and
SuperRegistersEqual(taicpu(hp1).oper[1]^.reg, taicpu(p).oper[1]^.reg) then
begin
TargetReg := taicpu(p).oper[1]^.reg;
{ Now look backwards to find a simple commutative operation: ADD,
IMUL (2-register version), OR, AND or XOR - whose destination
register is the same as TEST }
hp2 := p;
while GetLastInstruction(hp2, hp2) and (hp2.typ = ait_instruction) do
if RegInInstruction(TargetReg, hp2) then
begin
if MatchInstruction(hp2, [A_ADD, A_IMUL, A_OR, A_AND, A_XOR], [taicpu(p).opsize]) and
MatchOpType(taicpu(hp2), top_reg, top_reg) and
(taicpu(hp2).oper[1]^.reg = TargetReg) and
(taicpu(hp2).oper[0]^.reg <> TargetReg) then
begin
SourceReg := taicpu(hp2).oper[0]^.reg;
if
{ Make sure the MOV doesn't use the other register }
not RegInOp(SourceReg, taicpu(hp1).oper[0]^) and
{ And make sure the source register is not used afterwards }
not RegInUsedRegs(SourceReg, UsedRegs) then
begin
DebugMsg(SPeepholeOptimization + 'OpTest2OpTest (register swap) done', hp2);
taicpu(hp2).oper[0]^.reg := TargetReg;
taicpu(hp2).oper[1]^.reg := SourceReg;
if taicpu(p).oper[0]^.typ = top_reg then
taicpu(p).oper[0]^.reg := SourceReg;
taicpu(p).oper[1]^.reg := SourceReg;
IncludeRegInUsedRegs(SourceReg, UsedRegs);
AllocRegBetween(SourceReg, hp2, p, UsedRegs);
Include(OptsToCheck, aoc_ForceNewIteration);
{ We can still check the following optimisations since
the instruction is still a TEST }
end;
end;
Break;
end;
end;
{ Search ahead3 for CMOV instructions }
if (cs_opt_level2 in current_settings.optimizerswitches) then
begin
hp1 := p;