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Generate calls to ~ZERO to initialize large numbers of zero bytes.

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There is a tradeoff of code size vs. speed, since a sequence of STZ instructions is faster than a call to ~ZERO but could be quite large for a big array or struct. We now use ~ZERO for initializations of over 50 bytes to avoid excessive code bloat; the exact number chosen is somewhat arbitrary.
This commit is contained in:
Stephen Heumann 2022-12-03 15:30:31 -06:00
parent d56cf7e666
commit 945d5ce855
1 changed files with 19 additions and 30 deletions
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49
Parser.pas
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@ -4451,7 +4451,7 @@ var
{ count - number of times to re-use the initializer }
{ iPtr - pointer to the initializer record to use }
label 1,2,3;
label 1,2,3,4;
var
count: integer; {initializer counter}
@ -4479,31 +4479,6 @@ var
end; {LoadAddress}
function ZeroFill (elements: longint; itype: typePtr;
count: integer; iPtr: initializerPtr): boolean;
{ See if an array can be zero filled }
{ }
{ parameters: }
{ elements - elements in the array }
{ itype - type of each array element }
{ count - remaining initializer repetitions }
{ iPtr - initializer record }
begin {ZeroFill}
ZeroFill := false;
if not iPtr^.isConstant then
if itype^.kind in [scalarType,enumType] then
if count >= elements then
with iPtr^.itree^ do
if token.kind = intconst then
if token.ival = 0 then
{don't call ~ZERO for very small arrays}
if elements * itype^.size > 10 then
ZeroFill := true;
end; {ZeroFill}
procedure AddOperation;
{ Deal with a new initializer expression in a compound }
@ -4557,12 +4532,25 @@ var
isConstant := false;
end; {else}
if isConstant then {zero-initialize two bytes at a time}
if isConstant then
if val = 0 then
if count > 1 then
if itype^.size = 1 then begin
itype := shortPtr;
count := count - 1;
{call ~ZERO for > 50 zero bytes}
if count > 50 then begin
Gen0t(pc_stk, cgULong);
Gen1t(pc_ldc, count, cgWord);
Gen0t(pc_stk, cgWord);
Gen0t(pc_bno, cgWord);
Gen1tName(pc_cup, -1, cgVoid, @'~ZERO');
if isCompoundLiteral then
AddOperation;
goto 4;
end {if}
else begin {zero-initialize two bytes at a time}
itype := shortPtr;
count := count - 1;
end; {else}
end; {if}
{ if isConstant then
@ -4622,7 +4610,7 @@ var
Gen0t(pc_stk, cgULong);
Gen1t(pc_ldc, ord(elements), cgWord);
Gen0t(pc_stk, cgWord);
Gen0t(pc_bno, cgULong);
Gen0t(pc_bno, cgWord);
Gen1tName(pc_cup, -1, cgVoid, @'~ZERO');
if isCompoundLiteral then
AddOperation;
@ -4650,6 +4638,7 @@ var
disp := disp + itype^.size;
goto 3;
end; {if}
4:
end; {InitializeOneElement}