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8c, 6c: avoid allocating index registers when we don't have to

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when a operation receives a chain of OINDEX nodes as its operands,
each indexing step used to allocate a new index register. this
is wastefull an can result in running out of fixed registers on 386
for code such as: x = a[a[a[a[i]]]].

instead we attempt to reuse the destination register of the operation
as the index register if it is not otherwise referenced. this results
in the index chain to use a single register for index and result and
leaves registers free to be used for something usefull instead.

for 6c, try to avoid R13 as well as BP index base register.
This commit is contained in:
cinap_lenrek 2019-06-24 19:36:01 +02:00
parent 9f6967ed7e
commit 345714dd56
2 changed files with 45 additions and 9 deletions
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29
sys/src/cmd/6c/txt.c
View file

@ -1117,8 +1117,18 @@ gmove(Node *f, Node *t)
gins(a, f, t);
}
static int
regused(Node *n, int r)
{
if(n == nil)
return 0;
if(isreg(n, r))
return 1;
return regused(n->left, r) || regused(n->right, r);
}
void
doindex(Node *n)
doindex(Node *n, Node *o)
{
Node nod, nod1;
long v;
@ -1129,7 +1139,11 @@ prtree(n, "index");
if(n->left->complex >= FNX)
print("botch in doindex\n");
regalloc(&nod, &qregnode, Z);
if(n->right->op == OREGISTER)
o = n->right;
else if(o == Z || o->op != OREGISTER || regused(n, o->reg))
o = Z;
regalloc(&nod, &qregnode, o);
v = constnode.vconst;
cgen(n->right, &nod);
idx.ptr = D_NONE;
@ -1139,11 +1153,13 @@ print("botch in doindex\n");
idx.ptr = n->left->reg;
else if(n->left->op != OADDR) {
reg[D_BP]++; // cant be used as a base
reg[D_R13]++;
regalloc(&nod1, &qregnode, Z);
cgen(n->left, &nod1);
idx.ptr = nod1.reg;
regfree(&nod1);
reg[D_BP]--;
reg[D_R13]--;
}
idx.reg = nod.reg;
regfree(&nod);
@ -1155,9 +1171,14 @@ gins(int a, Node *f, Node *t)
{
if(f != Z && f->op == OINDEX)
doindex(f);
doindex(f, a == AMOVL || a == ALEAL
|| a == AMOVQ || a == ALEAQ
|| a == AMOVBLSX || a == AMOVBLZX
|| a == AMOVBQSX || a == AMOVBQZX
|| a == AMOVWLSX || a == AMOVWLZX
|| a == AMOVWQSX || a == AMOVWQZX ? t : Z);
if(t != Z && t->op == OINDEX)
doindex(t);
doindex(t, Z);
nextpc();
p->as = a;
if(f != Z)

25
sys/src/cmd/8c/txt.c
View file

@ -928,8 +928,18 @@ gmove(Node *f, Node *t)
gins(a, f, t);
}
static int
regused(Node *n, int r)
{
if(n == nil)
return 0;
if(isreg(n, r))
return 1;
return regused(n->left, r) || regused(n->right, r);
}
void
doindex(Node *n)
doindex(Node *n, Node *o)
{
Node nod, nod1;
long v;
@ -940,7 +950,11 @@ prtree(n, "index");
if(n->left->complex >= FNX)
print("botch in doindex\n");
regalloc(&nod, &regnode, Z);
if(n->right->op == OREGISTER)
o = n->right;
else if(o == Z || o->op != OREGISTER || regused(n, o->reg))
o = Z;
regalloc(&nod, &regnode, o);
v = constnode.vconst;
cgen(n->right, &nod);
idx.ptr = D_NONE;
@ -965,11 +979,12 @@ print("botch in doindex\n");
void
gins(int a, Node *f, Node *t)
{
if(f != Z && f->op == OINDEX)
doindex(f);
doindex(f, a == AMOVL || a == ALEAL
|| a == AMOVBLSX || a == AMOVBLZX
|| a == AMOVWLSX || a == AMOVWLZX ? t : Z);
if(t != Z && t->op == OINDEX)
doindex(t);
doindex(t, Z);
nextpc();
p->as = a;
if(f != Z)