runtime: zero at start of frame more efficiently.

Use Duff's device for zeroing.  Combine adjacent regions.

Update #7680
Update #7624

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/83200045

diff --git a/src/cmd/6g/ggen.c b/src/cmd/6g/ggen.c
index 6b159e2e37e29e716bc2dc494adcaa863d2840c8..51319f23dbfecac1875de697bef836f724bd0e7a 100644 (file)
--- a/src/cmd/6g/ggen.c
+++ b/src/cmd/6g/ggen.c
@@ -10,13 +10,14 @@
 #include "opt.h"
 
 static Prog *appendpp(Prog*, int, int, vlong, int, vlong);
+static Prog *zerorange(Prog *p, vlong frame, vlong lo, vlong hi, uint32 *ax);
 
 void
 defframe(Prog *ptxt)
 {
-       uint32 frame;
+       uint32 frame, ax;
        Prog *p;
-       vlong i;
+       vlong hi, lo;
        NodeList *l;
        Node *n;
 
@@ -28,14 +29,13 @@ defframe(Prog *ptxt)
        frame = rnd(stksize+maxarg, widthreg);
        ptxt->to.offset |= frame;
        
-       // insert code to contain ambiguously live variables
-       // so that garbage collector only sees initialized values
+       // insert code to zero ambiguously live variables
+       // so that the garbage collector only sees initialized values
        // when it looks for pointers.
-       //
-       // TODO: determine best way to zero the given values.
-       // among other problems, AX is initialized to 0 multiple times,
-       // but that's really the tip of the iceberg.
        p = ptxt;
+       lo = hi = 0;
+       ax = 0;
+       // iterate through declarations - they are sorted in decreasing xoffset order.
        for(l=curfn->dcl; l != nil; l = l->next) {
                n = l->n;
                if(!n->needzero)
@@ -44,21 +44,50 @@ defframe(Prog *ptxt)
                        fatal("needzero class %d", n->class);
                if(n->type->width % widthreg != 0 || n->xoffset % widthreg != 0 || n->type->width == 0)
                        fatal("var %lN has size %d offset %d", n, (int)n->type->width, (int)n->xoffset);
-               if(n->type->width <= 2*widthreg) {
-                       for(i = 0; i < n->type->width; i += widthreg)
-                               p = appendpp(p, AMOVQ, D_CONST, 0, D_SP+D_INDIR, frame+n->xoffset+i);
-               } else if(n->type->width <= 16*widthreg) {
-                       p = appendpp(p, AMOVQ, D_CONST, 0, D_AX, 0);
-                       for(i = 0; i < n->type->width; i += widthreg)
-                               p = appendpp(p, AMOVQ, D_AX, 0, D_SP+D_INDIR, frame+n->xoffset+i);
-               } else {
-                       p = appendpp(p, AMOVQ, D_CONST, 0, D_AX, 0);
-                       p = appendpp(p, AMOVQ, D_CONST, n->type->width/widthreg, D_CX, 0);
-                       p = appendpp(p, leaptr, D_SP+D_INDIR, frame+n->xoffset, D_DI, 0);
-                       p = appendpp(p, AREP, D_NONE, 0, D_NONE, 0);
-                       p = appendpp(p, ASTOSQ, D_NONE, 0, D_NONE, 0);
+
+               if(n->xoffset + n->type->width >= lo - 2*widthptr) {
+                       // merge with range we already have
+                       lo = n->xoffset;
+                       continue;
+               }
+               // zero old range
+               p = zerorange(p, frame, lo, hi, &ax);
+
+               // set new range
+               hi = n->xoffset + n->type->width;
+               lo = n->xoffset;
+       }
+       // zero final range
+       zerorange(p, frame, lo, hi, &ax);
+}
+
+static Prog*
+zerorange(Prog *p, vlong frame, vlong lo, vlong hi, uint32 *ax)
+{
+       vlong cnt, i;
+
+       cnt = hi - lo;
+       if(cnt == 0)
+               return p;
+       if(*ax == 0) {
+               p = appendpp(p, AMOVQ, D_CONST, 0, D_AX, 0);
+               *ax = 1;
+       }
+       if(cnt <= 4*widthreg) {
+               for(i = 0; i < cnt; i += widthreg) {
+                       p = appendpp(p, AMOVQ, D_AX, 0, D_SP+D_INDIR, frame+lo+i);
                }
+       } else if(cnt <= 128*widthreg) {
+               p = appendpp(p, leaptr, D_SP+D_INDIR, frame+lo, D_DI, 0);
+               p = appendpp(p, ADUFFZERO, D_NONE, 0, D_ADDR, 2*(128-cnt/widthreg));
+               p->to.sym = linksym(pkglookup("duffzero", runtimepkg));
+       } else {
+               p = appendpp(p, AMOVQ, D_CONST, cnt/widthreg, D_CX, 0);
+               p = appendpp(p, leaptr, D_SP+D_INDIR, frame+lo, D_DI, 0);
+               p = appendpp(p, AREP, D_NONE, 0, D_NONE, 0);
+               p = appendpp(p, ASTOSQ, D_NONE, 0, D_NONE, 0);
        }
+       return p;
 }
 
 static Prog*   

diff --git a/src/cmd/8g/ggen.c b/src/cmd/8g/ggen.c
index 8388e64bd50225f0e455762781080f838562da97..0a1523871e7029af74d3ab502452456d68e56ecd 100644 (file)
--- a/src/cmd/8g/ggen.c
+++ b/src/cmd/8g/ggen.c
@@ -10,13 +10,14 @@
 #include "opt.h"
 
 static Prog *appendpp(Prog*, int, int, vlong, int, vlong);
+static Prog *zerorange(Prog *p, vlong frame, vlong lo, vlong hi, uint32 *ax);
 
 void
 defframe(Prog *ptxt)
 {
-       uint32 frame;
+       uint32 frame, ax;
        Prog *p;
-       vlong i;
+       vlong lo, hi;
        NodeList *l;
        Node *n;
 
@@ -27,14 +28,12 @@ defframe(Prog *ptxt)
        frame = rnd(stksize+maxarg, widthptr);
        ptxt->to.offset = frame;
        
-       // insert code to contain ambiguously live variables
-       // so that garbage collector only sees initialized values
+       // insert code to zero ambiguously live variables
+       // so that the garbage collector only sees initialized values
        // when it looks for pointers.
-       //
-       // TODO: determine best way to zero the given values.
-       // among other problems, AX is initialized to 0 multiple times,
-       // but that's really the tip of the iceberg.
        p = ptxt;
+       lo = hi = 0;
+       ax = 0;
        for(l=curfn->dcl; l != nil; l = l->next) {
                n = l->n;
                if(!n->needzero)
@@ -43,21 +42,49 @@ defframe(Prog *ptxt)
                        fatal("needzero class %d", n->class);
                if(n->type->width % widthptr != 0 || n->xoffset % widthptr != 0 || n->type->width == 0)
                        fatal("var %lN has size %d offset %d", n, (int)n->type->width, (int)n->xoffset);
-               if(n->type->width <= 2*widthptr) {
-                       for(i = 0; i < n->type->width; i += widthptr)
-                               p = appendpp(p, AMOVL, D_CONST, 0, D_SP+D_INDIR, frame+n->xoffset+i);
-               } else if(n->type->width <= 16*widthptr) {
-                       p = appendpp(p, AMOVL, D_CONST, 0, D_AX, 0);
-                       for(i = 0; i < n->type->width; i += widthptr)
-                               p = appendpp(p, AMOVL, D_AX, 0, D_SP+D_INDIR, frame+n->xoffset+i);
-               } else {
-                       p = appendpp(p, AMOVL, D_CONST, 0, D_AX, 0);
-                       p = appendpp(p, AMOVL, D_CONST, n->type->width/widthptr, D_CX, 0);
-                       p = appendpp(p, ALEAL, D_SP+D_INDIR, frame+n->xoffset, D_DI, 0);
-                       p = appendpp(p, AREP, D_NONE, 0, D_NONE, 0);
-                       p = appendpp(p, ASTOSL, D_NONE, 0, D_NONE, 0);
+               if(n->xoffset + n->type->width == lo - 2*widthptr) {
+                       // merge with range we already have
+                       lo = n->xoffset;
+                       continue;
                }
+               // zero old range
+               p = zerorange(p, frame, lo, hi, &ax);
+
+               // set new range
+               hi = n->xoffset + n->type->width;
+               lo = n->xoffset;
+       }
+       // zero final range
+       zerorange(p, frame, lo, hi, &ax);
+}
+
+static Prog*
+zerorange(Prog *p, vlong frame, vlong lo, vlong hi, uint32 *ax)
+{
+       vlong cnt, i;
+
+       cnt = hi - lo;
+       if(cnt == 0)
+               return p;
+       if(*ax == 0) {
+               p = appendpp(p, AMOVL, D_CONST, 0, D_AX, 0);
+               *ax = 1;
+       }
+       if(cnt <= 4*widthreg) {
+               for(i = 0; i < cnt; i += widthreg) {
+                       p = appendpp(p, AMOVL, D_AX, 0, D_SP+D_INDIR, frame+lo+i);
+               }
+       } else if(cnt <= 128*widthreg) {
+               p = appendpp(p, ALEAL, D_SP+D_INDIR, frame+lo, D_DI, 0);
+               p = appendpp(p, ADUFFZERO, D_NONE, 0, D_ADDR, 1*(128-cnt/widthreg));
+               p->to.sym = linksym(pkglookup("duffzero", runtimepkg));
+       } else {
+               p = appendpp(p, AMOVL, D_CONST, cnt/widthreg, D_CX, 0);
+               p = appendpp(p, ALEAL, D_SP+D_INDIR, frame+lo, D_DI, 0);
+               p = appendpp(p, AREP, D_NONE, 0, D_NONE, 0);
+               p = appendpp(p, ASTOSL, D_NONE, 0, D_NONE, 0);
        }
+       return p;
 }
 
 static Prog*