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+ optimized division by negative power of 2 constants in the i8086 code

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generator as well

git-svn-id: trunk@37004 -
This commit is contained in:
nickysn 2017-08-21 11:56:11 +00:00
parent 6634141bf4
commit aa415bfc6b
1 changed files with 11 additions and 7 deletions
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18
compiler/i8086/n8086mat.pas
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@ -103,6 +103,7 @@ implementation
e : smallint;
d,l,r,s,m,a,n,t : word;
m_low,m_high,j,k : dword;
invertsign: Boolean;
begin
secondpass(left);
if codegenerror then
@ -121,13 +122,14 @@ implementation
if (nodetype=divn) and (right.nodetype=ordconstn) then
begin
if ispowerof2(tordconstnode(right).value.svalue,power) then
if isabspowerof2(tordconstnode(right).value,power) then
begin
{ for signed numbers, the numerator must be adjusted before the
shift instruction, but not wih unsigned numbers! Otherwise,
"Cardinal($ffffffff) div 16" overflows! (JM) }
if is_signed(left.resultdef) Then
begin
invertsign:=tordconstnode(right).value<0;
if (current_settings.optimizecputype > cpu_386) and
not(cs_opt_size in current_settings.optimizerswitches) then
{ use a sequence without jumps, saw this in
@ -136,17 +138,17 @@ implementation
{ no jumps, but more operations }
hreg2:=cg.getintregister(current_asmdata.CurrAsmList,OS_INT);
emit_reg_reg(A_MOV,S_W,hreg1,hreg2);
if tordconstnode(right).value=2 then
if power=1 then
begin
{If the left value is negative, hreg2=(right value-1)=1, otherwise 0.}
{If the left value is negative, hreg2=(1 shl power)-1=1, otherwise 0.}
cg.a_op_const_reg(current_asmdata.CurrAsmList,OP_SHR,OS_16,15,hreg2);
end
else
begin
{If the left value is negative, hreg2=$ffff, otherwise 0.}
cg.a_op_const_reg(current_asmdata.CurrAsmList,OP_SAR,OS_16,15,hreg2);
{If negative, hreg2=right value-1, otherwise 0.}
emit_const_reg(A_AND,S_W,tordconstnode(right).value.svalue-1,hreg2);
{If negative, hreg2=(1 shl power)-1, otherwise 0.}
emit_const_reg(A_AND,S_W,(aint(1) shl power)-1,hreg2);
end;
{ add to the left value }
emit_reg_reg(A_ADD,S_W,hreg2,hreg1);
@ -162,10 +164,12 @@ implementation
if power=1 then
emit_reg(A_INC,S_W,hreg1)
else
emit_const_reg(A_ADD,S_W,tordconstnode(right).value.svalue-1,hreg1);
emit_const_reg(A_ADD,S_W,(aint(1) shl power)-1,hreg1);
cg.a_label(current_asmdata.CurrAsmList,hl);
cg.a_op_const_reg(current_asmdata.CurrAsmList,OP_SAR,OS_16,power,hreg1);
end
end;
if invertsign then
emit_reg(A_NEG,S_W,hreg1);
end
else
cg.a_op_const_reg(current_asmdata.CurrAsmList,OP_SHR,OS_16,power,hreg1);