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gc: O(1) string comparison when lengths differ

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R=ken2
CC=golang-dev
https://golang.org/cl/2331045
This commit is contained in:
Russ Cox 2010-10-06 09:53:12 -04:00
parent 30edda690f
commit 30dd191171
7 changed files with 56 additions and 9 deletions
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3
src/cmd/5g/cgen.c
View File

@ -820,6 +820,9 @@ bgen(Node *n, int true, Prog *to)
if(n == N)
n = nodbool(1);
if(n->ninit != nil)
genlist(n->ninit);
nl = n->left;
nr = n->right;

3
src/cmd/6g/cgen.c
View File

@ -699,6 +699,9 @@ bgen(Node *n, int true, Prog *to)
if(n == N)
n = nodbool(1);
if(n->ninit != nil)
genlist(n->ninit);
nl = n->left;
nr = n->right;

3
src/cmd/8g/cgen.c
View File

@ -754,6 +754,9 @@ bgen(Node *n, int true, Prog *to)
if(n == N)
n = nodbool(1);
if(n->ninit != nil)
genlist(n->ninit);
nl = n->left;
nr = n->right;

6
src/cmd/gc/gen.c
View File

@ -248,9 +248,6 @@ gen(Node *n)
gen(n->nincr); // contin: incr
patch(p1, pc); // test:
if(n->ntest != N)
if(n->ntest->ninit != nil)
genlist(n->ntest->ninit);
bgen(n->ntest, 0, breakpc); // if(!test) goto break
genlist(n->nbody); // body
gjmp(continpc);
@ -263,9 +260,6 @@ gen(Node *n)
p1 = gjmp(P); // goto test
p2 = gjmp(P); // p2: goto else
patch(p1, pc); // test:
if(n->ntest != N)
if(n->ntest->ninit != nil)
genlist(n->ntest->ninit);
bgen(n->ntest, 0, p2); // if(!test) goto p2
genlist(n->nbody); // then
p3 = gjmp(P); // goto done

1
src/cmd/gc/go.h
View File

@ -1109,6 +1109,7 @@ Type* ptrto(Type *t);
void* remal(void *p, int32 on, int32 n);
Sym* restrictlookup(char *name, Pkg *pkg);
Node* safeexpr(Node *n, NodeList **init);
Node* cheapexpr(Node *n, NodeList **init);
int32 setlineno(Node *n);
void setmaxarg(Type *t);
Type* shallow(Type *t);

20
src/cmd/gc/subr.c
View File

@ -2595,7 +2595,7 @@ brrev(int a)
}
/*
* return side effect-free appending side effects to init.
* return side effect-free n, appending side effects to init.
* result is assignable if n is.
*/
Node*
@ -2652,6 +2652,24 @@ safeexpr(Node *n, NodeList **init)
// make a copy; must not be used as an lvalue
if(islvalue(n))
fatal("missing lvalue case in safeexpr: %N", n);
return cheapexpr(n, init);
}
/*
* return side-effect free and cheap n, appending side effects to init.
* result may not be assignable.
*/
Node*
cheapexpr(Node *n, NodeList **init)
{
Node *a, *l;
switch(n->op) {
case ONAME:
case OLITERAL:
return n;
}
l = nod(OXXX, N, N);
tempname(l, n->type);
a = nod(OAS, l, n);

29
src/cmd/gc/walk.c
View File

@ -654,8 +654,6 @@ walkexpr(Node **np, NodeList **init)
case OAND:
case OOR:
case OXOR:
case OANDAND:
case OOROR:
case OSUB:
case OMUL:
case OEQ:
@ -669,6 +667,17 @@ walkexpr(Node **np, NodeList **init)
walkexpr(&n->left, init);
walkexpr(&n->right, init);
goto ret;
case OANDAND:
case OOROR:
walkexpr(&n->left, init);
// cannot put side effects from n->right on init,
// because they cannot run before n->left is checked.
// save elsewhere and store on the eventual n->right.
ll = nil;
walkexpr(&n->right, &ll);
n->right->ninit = concat(n->right->ninit, ll);
goto ret;
case OPRINT:
case OPRINTN:
@ -1196,11 +1205,27 @@ walkexpr(Node **np, NodeList **init)
goto ret;
}
// prepare for rewrite below
if(n->etype == OEQ || n->etype == ONE) {
n->left = cheapexpr(n->left, init);
n->right = cheapexpr(n->right, init);
}
// sys_cmpstring(s1, s2) :: 0
r = mkcall("cmpstring", types[TINT], init,
conv(n->left, types[TSTRING]),
conv(n->right, types[TSTRING]));
r = nod(n->etype, r, nodintconst(0));
// quick check of len before full compare for == or !=
if(n->etype == OEQ || n->etype == ONE) {
if(n->etype == OEQ)
r = nod(OANDAND, nod(OEQ, nod(OLEN, n->left, N), nod(OLEN, n->right, N)), r);
else
r = nod(OOROR, nod(ONE, nod(OLEN, n->left, N), nod(OLEN, n->right, N)), r);
typecheck(&r, Erv);
walkexpr(&r, nil);
}
typecheck(&r, Erv);
n = r;
goto ret;