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cmd/5g, cmd/6g, cmd/8g: preserve wide values in large functions 

In large functions with many variables, the register optimizer
may give up and choose not to track certain variables at all.
In this case, the "nextinnode" information linking together
all the words from a given variable will be incomplete, and
the result may be that only some of a multiword value is
preserved across a call. That confuses the garbage collector,
so don't do that. Instead, mark those variables as having
their address taken, so that they will be preserved at all
calls. It's overkill, but correct.

Tested by hand using the 6g -S output to see that it does fix
the buggy generated code leading to the issue 7726 failure.

There is no automated test because I managed to break the
compiler while writing a test (see issue 7727). I will check
in a test along with the fix to issue 7727.

Fixes #7726.

LGTM=khr
R=khr, bradfitz, dave
CC=golang-codereviews
https://golang.org/cl/85200043
This commit is contained in:
Russ Cox 2014-04-16 13:59:42 -04:00
parent 59f6c81f98
commit 0a8a719ded
3 changed files with 30 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/cmd/5g/reg.c
View File

@ -801,6 +801,16 @@ mkvar(Reg *r, Adr *a)
if(nvar >= NVAR) {
if(debug['w'] > 1 && node)
fatal("variable not optimized: %D", a);
// If we're not tracking a word in a variable, mark the rest as
// having its address taken, so that we keep the whole thing
// live at all calls. otherwise we might optimize away part of
// a variable but not all of it.
for(i=0; i<nvar; i++) {
v = var+i;
if(v->node == node)
v->addr = 1;
}
goto none;
}

10
src/cmd/6g/reg.c
View File

@ -659,6 +659,16 @@ mkvar(Reg *r, Adr *a)
if(nvar >= NVAR) {
if(debug['w'] > 1 && node != N)
fatal("variable not optimized: %#N", node);
// If we're not tracking a word in a variable, mark the rest as
// having its address taken, so that we keep the whole thing
// live at all calls. otherwise we might optimize away part of
// a variable but not all of it.
for(i=0; i<nvar; i++) {
v = var+i;
if(v->node == node)
v->addr = 1;
}
goto none;
}

10
src/cmd/8g/reg.c
View File

@ -625,6 +625,16 @@ mkvar(Reg *r, Adr *a)
if(nvar >= NVAR) {
if(debug['w'] > 1 && node != N)
fatal("variable not optimized: %D", a);
// If we're not tracking a word in a variable, mark the rest as
// having its address taken, so that we keep the whole thing
// live at all calls. otherwise we might optimize away part of
// a variable but not all of it.
for(i=0; i<nvar; i++) {
v = var+i;
if(v->node == node)
v->addr = 1;
}
goto none;
}