cmd/gc: make liveness ~10x faster

1) The arrayindexof lookup function is O(n). Replace with O(1) lookups.

2) The checkptxt function is O(n²) and is purely for debugging.
Only run when the debugging flags are turned on.

3) Iterating over sparse bitmaps can be done faster word by word.
Introduce and use bvnext for that.

Run times before and after, on my 2.5 GHz Core i5 MacBook Pro.

x.go       9.48  0.84  issue 8259

x100.go    0.01  0.01  issue 8354
x1000.go   0.10  0.10
x2000.go   0.62  0.19
x3000.go   1.33  0.34
x4000.go   2.29  0.49
x5000.go   3.89  0.67
x6000.go   5.00  0.90
x7000.go   6.70  1.13
x8000.go   9.44  1.38
x9000.go  11.23  1.87
x10000.go 13.78  2.09

Fixes #8259.
Fixes #8354.

LGTM=iant, r
R=golang-codereviews, iant, r
CC=golang-codereviews
https://golang.org/cl/125720043

diff --git a/src/cmd/gc/array.c b/src/cmd/gc/array.c
index 5e53c1ff0e2e62b93e4f5075ef9c77f54fa1fcb9..611fc9fbd406d2ee408585559d9715b3388384a7 100644 (file)
--- a/src/cmd/gc/array.c
+++ b/src/cmd/gc/array.c
@@ -108,20 +108,6 @@ arrayadd(Array *array, void *element)
        arrayset(array, array->length - 1, element);
 }
 
-int32
-arrayindexof(Array *array, void *element)
-{
-       void *p;
-       int32 i;
-
-       for(i = 0; i < array->length; i++) {
-               p = arrayget(array, i);
-               if(memcmp(p, &element, array->size) == 0)
-                       return i;
-       }
-       return -1;
-}
-
 void
 arraysort(Array *array, int (*cmp)(const void*, const void*))
 {

diff --git a/src/cmd/gc/bv.c b/src/cmd/gc/bv.c
index 2efbbc565e338d5b1fd128a09627610398b796b7..0e8f8d47394771179ed6aa37911a1ae7e6f7e430 100644 (file)
--- a/src/cmd/gc/bv.c
+++ b/src/cmd/gc/bv.c
@@ -9,6 +9,8 @@
 enum {
        WORDSIZE = sizeof(uint32),
        WORDBITS = 32,
+       WORDMASK = WORDBITS - 1,
+       WORDSHIFT = 5,
 };
 
 static uintptr
@@ -94,13 +96,35 @@ bvconcat(Bvec *src1, Bvec *src2)
 int
 bvget(Bvec *bv, int32 i)
 {
-       uint32 mask, word;
-
        if(i < 0 || i >= bv->n)
                fatal("bvget: index %d is out of bounds with length %d\n", i, bv->n);
-       mask = 1U << (i % WORDBITS);
-       word = bv->b[i / WORDBITS] & mask;
-       return word ? 1 : 0;
+       return (bv->b[i>>WORDSHIFT] >> (i&WORDMASK)) & 1;
+}
+
+// bvnext returns the smallest index >= i for which bvget(bv, i) == 1.
+// If there is no such index, bvnext returns -1.
+int
+bvnext(Bvec *bv, int32 i)
+{
+       uint32 w;
+
+       // Jump i ahead to next word with bits.
+       if((bv->b[i>>WORDSHIFT]>>(i&WORDMASK)) == 0) {
+               i &= ~WORDMASK;
+               i += WORDBITS;
+               while(i < bv->n && bv->b[i>>WORDSHIFT] == 0)
+                       i += WORDBITS;
+       }
+       if(i >= bv->n)
+               return -1;
+       
+       // Find 1 bit.
+       w = bv->b[i>>WORDSHIFT]>>(i&WORDMASK);
+       while((w&1) == 0) {
+               w>>=1;
+               i++;
+       }
+       return i;
 }
 
 int
@@ -109,7 +133,7 @@ bvisempty(Bvec *bv)
        int32 i;
 
        for(i = 0; i < bv->n; i += WORDBITS)
-               if(bv->b[i / WORDBITS] != 0)
+               if(bv->b[i>>WORDSHIFT] != 0)
                        return 0;
        return 1;
 }

diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 30b210f92e57d2d5764a703f8c36d22080ff3223..c3da5f636a388e7793e5833190e6d3d83333170f 100644 (file)
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -1017,7 +1017,6 @@ int32     arraylength(Array *array);
 void*  arrayget(Array *array, int32 index);
 void   arrayset(Array *array, int32 index, void *element);
 void   arrayadd(Array *array, void *element);
-int32  arrayindexof(Array* array, void *element);
 void   arraysort(Array* array, int (*cmp)(const void*, const void*));
 
 /*
@@ -1043,6 +1042,7 @@ int       bvcmp(Bvec *bv1, Bvec *bv2);
 void   bvcopy(Bvec *dst, Bvec *src);
 Bvec*  bvconcat(Bvec *src1, Bvec *src2);
 int    bvget(Bvec *bv, int32 i);
+int32  bvnext(Bvec *bv, int32 i);
 int    bvisempty(Bvec *bv);
 void   bvnot(Bvec *bv);
 void   bvor(Bvec *dst, Bvec *src1, Bvec *src2);

diff --git a/src/cmd/gc/plive.c b/src/cmd/gc/plive.c
index 9026f6003e81b1fb82f5d710bd1119155312b310..e67b0af757b484ec26d357548c5e5e93258ce44d 100644 (file)
--- a/src/cmd/gc/plive.c
+++ b/src/cmd/gc/plive.c
@@ -283,13 +283,30 @@ getvariables(Node *fn)
                        // For arguments and results, the bitmap covers all variables,
                        // so we must include all the variables, even the ones without
                        // pointers.
+                       //
+                       // The Node.opt field is available for use by optimization passes.
+                       // We use it to hold the index of the node in the variables array, plus 1
+                       // (so that 0 means the Node is not in the variables array).
+                       // Each pass should clear opt when done, but you never know,
+                       // so clear them all ourselves too.
+                       // The Node.curfn field is supposed to be set to the current function
+                       // already, but for some compiler-introduced names it seems not to be,
+                       // so fix that here.
+                       // Later, when we want to find the index of a node in the variables list,
+                       // we will check that n->curfn == curfn and n->opt > 0. Then n->opt - 1
+                       // is the index in the variables list.
+                       ll->n->opt = nil;
+                       ll->n->curfn = curfn;
                        switch(ll->n->class) {
                        case PAUTO:
-                               if(haspointers(ll->n->type))
+                               if(haspointers(ll->n->type)) {
+                                       ll->n->opt = (void*)(uintptr)(arraylength(result)+1);
                                        arrayadd(result, &ll->n);
+                               }
                                break;
                        case PPARAM:
                        case PPARAMOUT:
+                               ll->n->opt = (void*)(uintptr)(arraylength(result)+1);
                                arrayadd(result, &ll->n);
                                break;
                        }
@@ -718,14 +735,16 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
        }
        if(info.flags & (LeftRead | LeftWrite | LeftAddr)) {
                from = &prog->from;
-               if (from->node != nil && from->sym != nil) {
+               if (from->node != nil && from->sym != nil && from->node->curfn == curfn) {
                        switch(from->node->class & ~PHEAP) {
                        case PAUTO:
                        case PPARAM:
                        case PPARAMOUT:
-                               pos = arrayindexof(vars, from->node);
+                               pos = (int)(uintptr)from->node->opt - 1; // index in vars
                                if(pos == -1)
                                        goto Next;
+                               if(pos >= arraylength(vars) || *(Node**)arrayget(vars, pos) != from->node)
+                                       fatal("bad bookkeeping in liveness %N %d", from->node, pos);
                                if(from->node->addrtaken) {
                                        bvset(avarinit, pos);
                                } else {
@@ -741,14 +760,16 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
 Next:
        if(info.flags & (RightRead | RightWrite | RightAddr)) {
                to = &prog->to;
-               if (to->node != nil && to->sym != nil) {
+               if (to->node != nil && to->sym != nil && to->node->curfn == curfn) {
                        switch(to->node->class & ~PHEAP) {
                        case PAUTO:
                        case PPARAM:
                        case PPARAMOUT:
-                               pos = arrayindexof(vars, to->node);
+                               pos = (int)(uintptr)to->node->opt - 1; // index in vars
                                if(pos == -1)
                                        goto Next1;
+                               if(pos >= arraylength(vars) || *(Node**)arrayget(vars, pos) != to->node)
+                                       fatal("bad bookkeeping in liveness %N %d", to->node, pos);
                                if(to->node->addrtaken) {
                                        if(prog->as != AVARKILL)
                                                bvset(avarinit, pos);
@@ -1020,6 +1041,9 @@ checkptxt(Node *fn, Prog *firstp)
 {
        Prog *p;
 
+       if(debuglive == 0)
+               return;
+
        for(p = firstp; p != P; p = p->link) {
                if(0)
                        print("analyzing '%P'\n", p);
@@ -1172,21 +1196,17 @@ twobitlivepointermap(Liveness *lv, Bvec *liveout, Array *vars, Bvec *args, Bvec
        vlong xoffset;
        int32 i;
 
-       for(i = 0; i < arraylength(vars); i++) {
+       for(i = 0; (i = bvnext(liveout, i)) >= 0; i++) {
                node = *(Node**)arrayget(vars, i);
                switch(node->class) {
                case PAUTO:
-                       if(bvget(liveout, i)) {
-                               xoffset = node->xoffset + stkptrsize;
-                               twobitwalktype1(node->type, &xoffset, locals);
-                       }
+                       xoffset = node->xoffset + stkptrsize;
+                       twobitwalktype1(node->type, &xoffset, locals);
                        break;
                case PPARAM:
                case PPARAMOUT:
-                       if(bvget(liveout, i)) {
-                               xoffset = node->xoffset;
-                               twobitwalktype1(node->type, &xoffset, args);
-                       }
+                       xoffset = node->xoffset;
+                       twobitwalktype1(node->type, &xoffset, args);
                        break;
                }
        }
@@ -1944,6 +1964,7 @@ liveness(Node *fn, Prog *firstp, Sym *argssym, Sym *livesym)
        Array *cfg, *vars;
        Liveness *lv;
        int debugdelta;
+       NodeList *l;
 
        // Change name to dump debugging information only for a specific function.
        debugdelta = 0;
@@ -1984,6 +2005,9 @@ liveness(Node *fn, Prog *firstp, Sym *argssym, Sym *livesym)
        twobitwritesymbol(lv->argslivepointers, argssym);
 
        // Free everything.
+       for(l=fn->dcl; l != nil; l = l->next)
+               if(l->n != N)
+                       l->n->opt = nil;
        freeliveness(lv);
        arrayfree(vars);
        freecfg(cfg);