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Generate even better code for constant returns.

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If the return value is just a numeric constant or static address, it can simply be loaded right before the RTL instruction, avoiding any data movement.

This could actually be applied to a somewhat broader class of expressions, but for now it only applies to numeric or address constants, for which it is clearly correct.
This commit is contained in:
Stephen Heumann 2022-12-19 21:18:41 -06:00
parent e910eda623
commit 854a6779a9
1 changed files with 39 additions and 20 deletions
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59
Gen.pas
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@ -6975,29 +6975,37 @@ procedure GenTree {op: icptr};
size: integer; {localSize + parameterSize}
lab1: integer; {label}
valuePushed: boolean; {return value pushed on stack?}
evaluateAtEnd: boolean; {evaluate return val right before rtl?}
begin {GenRetRev}
size := localSize + parameterSize;
evaluateAtEnd := false;
{calculate return value, if necessary}
if op^.opcode = pc_rev then begin
valuePushed := namePushed or debugFlag or profileFlag
or ((parameterSize <> 0) and (size > 253));
if valuePushed then
gLong.preference := onStack
else
gLong.preference := A_X;
GenTree(op^.left);
if op^.optype in [cgByte,cgUByte,cgWord,cgUWord] then begin
if valuePushed then
GenImplied(m_pha)
else
GenImplied(m_tay);
if op^.left^.opcode in [pc_ldc,pc_lca,pc_lao,pc_lad] then begin
evaluateAtEnd := true;
valuePushed := false;
end {if}
else {if op^.optype in [cgLong,cgULong] then} begin
valuePushed := gLong.where = onStack;
if not valuePushed then
GenImplied(m_tay);
else begin
valuePushed := namePushed or debugFlag or profileFlag
or ((parameterSize <> 0) and (size > 253));
if valuePushed then
gLong.preference := onStack
else
gLong.preference := A_X;
GenTree(op^.left);
if op^.optype in [cgByte,cgUByte,cgWord,cgUWord] then begin
if valuePushed then
GenImplied(m_pha)
else
GenImplied(m_tay);
end {if}
else {if op^.optype in [cgLong,cgULong] then} begin
valuePushed := gLong.where = onStack;
if not valuePushed then
GenImplied(m_tay);
end; {else}
end; {else}
end;
@ -7048,8 +7056,9 @@ procedure GenTree {op: icptr};
if op^.optype in [cgLong,cgULong] then
GenImplied(m_plx);
end {if}
else if size = 2 then
GenImplied(m_tya);
else if not evaluateAtEnd then
if size = 2 then
GenImplied(m_tya);
end {if}
else
case op^.optype of {load the value to return}
@ -7121,14 +7130,24 @@ procedure GenTree {op: icptr};
{put return value in correct place}
case op^.optype of
cgByte,cgUByte,cgWord,cgUWord: begin
if size <> 2 then
if evaluateAtEnd then
GenTree(op^.left)
else if size <> 2 then
GenImplied(m_tya);
if toolParms then {save value on stack for tools}
GenNative(m_sta_s, direct, returnSize+1, nil, 0);
end;
cgLong,cgULong,cgReal,cgDouble,cgComp,cgExtended: begin
if size <> 2 then
if evaluateAtEnd then begin
gLong.preference := A_X;
GenTree(op^.left);
if gLong.where = onStack then begin
GenImplied(m_pla);
GenImplied(m_plx);
end; {if}
end {if}
else if size <> 2 then
GenImplied(m_tya);
if toolParms then begin {save value on stack for tools}
GenNative(m_sta_s, direct, returnSize+1, nil, 0);