diff options
author | Russ Cox <rsc@golang.org> | 2014-02-13 20:59:39 -0500 |
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committer | Russ Cox <rsc@golang.org> | 2014-02-13 20:59:39 -0500 |
commit | e0ed119d47728176de20aedeb519e6b470e7e411 (patch) | |
tree | eaaf55c2dd390512ef6c54ada8e4bab5b7c83842 /src | |
parent | 627d914dff9f9b31d835a6aaa57073364c13638a (diff) | |
download | go-e0ed119d47728176de20aedeb519e6b470e7e411.tar.gz |
cmd/gc: distinguish unnamed vs blank-named return variables better
Before, an unnamed return value turned into an ONAME node n with n->sym
named ~anon%d, and n->orig == n.
A blank-named return value turned into an ONAME node n with n->sym
named ~anon%d but n->orig == the original blank n. Code generation and
printing uses n->orig, so that this node formatted as _.
But some code does not use n->orig. In particular the liveness code does
not know about the n->orig convention and so mishandles blank identifiers.
It is possible to fix but seemed better to avoid the confusion entirely.
Now the first kind of node is named ~r%d and the second ~b%d; both have
n->orig == n, so that it doesn't matter whether code uses n or n->orig.
After this change the ->orig field is only used for other kinds of expressions,
not for ONAME nodes.
This requires distinguishing ~b from ~r names in a few places that care.
It fixes a liveness analysis bug without actually changing the liveness code.
TBR=ken2
CC=golang-codereviews
https://codereview.appspot.com/63630043
Diffstat (limited to 'src')
-rw-r--r-- | src/cmd/gc/dcl.c | 22 | ||||
-rw-r--r-- | src/cmd/gc/fmt.c | 16 | ||||
-rw-r--r-- | src/cmd/gc/walk.c | 2 |
3 files changed, 27 insertions, 13 deletions
diff --git a/src/cmd/gc/dcl.c b/src/cmd/gc/dcl.c index 7df1d97a8..d105c74f6 100644 --- a/src/cmd/gc/dcl.c +++ b/src/cmd/gc/dcl.c @@ -643,8 +643,8 @@ funcargs(Node *nt) fatal("funcargs out %O", n->op); if(n->left == N) { - // give it a name so escape analysis has nodes to work with - snprint(namebuf, sizeof(namebuf), "~anon%d", gen++); + // Name so that escape analysis can track it. ~r stands for 'result'. + snprint(namebuf, sizeof(namebuf), "~r%d", gen++); n->left = newname(lookup(namebuf)); // TODO: n->left->missing = 1; } @@ -652,14 +652,20 @@ funcargs(Node *nt) n->left->op = ONAME; if(isblank(n->left)) { - // Give it a name so we can assign to it during return. - // preserve the original in ->orig + // Give it a name so we can assign to it during return. ~b stands for 'blank'. + // The name must be different from ~r above because if you have + // func f() (_ int) + // func g() int + // f is allowed to use a plain 'return' with no arguments, while g is not. + // So the two cases must be distinguished. + // We do not record a pointer to the original node (n->orig). + // Having multiple names causes too much confusion in later passes. nn = nod(OXXX, N, N); *nn = *n->left; + nn->orig = nn; + snprint(namebuf, sizeof(namebuf), "~b%d", gen++); + nn->sym = lookup(namebuf); n->left = nn; - - snprint(namebuf, sizeof(namebuf), "~anon%d", gen++); - n->left->sym = lookup(namebuf); } n->left->ntype = n->right; @@ -1209,7 +1215,7 @@ functype(Node *this, NodeList *in, NodeList *out) t->outnamed = 0; if(t->outtuple > 0 && out->n->left != N && out->n->left->orig != N) { s = out->n->left->orig->sym; - if(s != S && s->name[0] != '~') + if(s != S && s->name[0] != '~' || s->name[1] != 'r') // ~r%d is the name invented for an unnamed result t->outnamed = 1; } diff --git a/src/cmd/gc/fmt.c b/src/cmd/gc/fmt.c index 6f40c7ff3..bffe8dfc7 100644 --- a/src/cmd/gc/fmt.c +++ b/src/cmd/gc/fmt.c @@ -678,12 +678,17 @@ typefmt(Fmt *fp, Type *t) if(!(fp->flags&FmtShort)) { s = t->sym; - // Take the name from the original, lest we substituted it with ~anon%d + // Take the name from the original, lest we substituted it with ~r%d or ~b%d. + // ~r%d is a (formerly) unnamed result. if ((fmtmode == FErr || fmtmode == FExp) && t->nname != N) { if(t->nname->orig != N) { s = t->nname->orig->sym; - if(s != S && s->name[0] == '~') - s = S; + if(s != S && s->name[0] == '~') { + if(s->name[1] == 'r') // originally an unnamed result + s = S; + else if(s->name[1] == 'b') // originally the blank identifier _ + s = lookup("_"); + } } else s = S; } @@ -1104,7 +1109,10 @@ exprfmt(Fmt *f, Node *n, int prec) case PAUTO: case PPARAM: case PPARAMOUT: - if(fmtmode == FExp && n->sym && !isblanksym(n->sym) && n->vargen > 0) + // _ becomes ~b%d internally; print as _ for export + if(fmtmode == FExp && n->sym && n->sym->name[0] == '~' && n->sym->name[1] == 'b') + return fmtprint(f, "_"); + if(fmtmode == FExp && n->sym && !isblank(n) && n->vargen > 0) return fmtprint(f, "%S·%d", n->sym, n->vargen); } diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c index eb5a3f1b6..1bceae998 100644 --- a/src/cmd/gc/walk.c +++ b/src/cmd/gc/walk.c @@ -2430,7 +2430,7 @@ paramstoheap(Type **argin, int out) nn = nil; for(t = structfirst(&savet, argin); t != T; t = structnext(&savet)) { v = t->nname; - if(v && v->sym && v->sym->name[0] == '~') + if(v && v->sym && v->sym->name[0] == '~' && v->sym->name[1] == 'r') // unnamed result v = N; // In precisestack mode, the garbage collector assumes results // are always live, so zero them always. |