From: David Given <dg@cowlark.com>
Date: Sat, 21 Jan 2017 22:22:54 +0000 (+0100)
Subject: Add basic freezing code. Rework the actual allocation phase to do it in the
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=f2e21ee1b6b5cc7e4d1f1536ce7517a5ed92849e;p=ack.git

Add basic freezing code. Rework the actual allocation phase to do it in the
right order. Disable spilling (as it's not working yet). Now the results look
almost correct, sometimes!
---

diff --git a/mach/proto/mcg/hop.c b/mach/proto/mcg/hop.c
index 4753bf99d..a0589f65d 100644
--- a/mach/proto/mcg/hop.c
+++ b/mach/proto/mcg/hop.c
@@ -242,7 +242,9 @@ static struct vreg* actual(struct vreg* vreg)
 
 void appendvreg(struct vreg* vreg)
 {
-    appendf("%%%d=%d", vreg->id, vreg->hreg);
+    appendf("%%%d", vreg->id);
+    if (vreg->hreg != -1)
+        appendf("=%d", vreg->hreg);
     if (vreg->is_spilt)
         appendf("S");
 }
diff --git a/mach/proto/mcg/pass_registerallocator.c b/mach/proto/mcg/pass_registerallocator.c
index 15c19e474..5a23d05f5 100644
--- a/mach/proto/mcg/pass_registerallocator.c
+++ b/mach/proto/mcg/pass_registerallocator.c
@@ -13,6 +13,7 @@ static const int DEGREE = 5;
 
 static struct graph interference;
 static struct graph affinity;
+static ARRAYOF(struct vreg) simplified;
 
 static struct vreg* actual(struct vreg* vreg)
 {
@@ -25,7 +26,6 @@ static void coalesce(struct vreg* vmaster, struct vreg* vslave)
 {
     vmaster = actual(vmaster);
     vslave = actual(vslave);
-    bitmap_or(&vmaster->bitmap, 32, &vslave->bitmap);
     vmaster->needs_register |= vslave->needs_register;
     vslave->coalesced_with = vmaster;
 }
@@ -69,9 +69,11 @@ static void generate_graph(void)
                 while (hashtable_next(hop->valueusage, &hit2))
                 {
                     struct valueusage* usage2 = hit2.value;
-                    if (usage1 == usage2)
-                        continue;
 
+                    if (usage1->invreg)
+                        graph_add_vertex(&interference, actual(usage1->invreg));
+                    if (usage2->invreg)
+                        graph_add_vertex(&interference, actual(usage2->invreg));
                     if (usage1->invreg && usage2->invreg)
                         graph_add_edge(&interference, actual(usage1->invreg), actual(usage2->invreg));
                     if (usage1->outvreg && usage2->outvreg)
@@ -219,19 +221,21 @@ static bool attempt_to_simplify(void)
     if (!vreg || (degree > DEGREE))
         return false;
 
-    /* Allocate a register. */
+    /* Push first the neighbours, and then the node itself annotated with the number
+     * of neighbours, to the simplification stack. */
 
-    vreg->hreg = bitmap_find_unset_bit(&vreg->bitmap, 32);
-    tracef('R', "R: simplifying vreg %%%d with degree %d and bitmap 0x%x to hreg %d\n",
-        vreg->id, degree, vreg->bitmap, vreg->hreg);
+    tracef('R', "R: simplifying vreg %%%d with degree %d\n", vreg->id, degree);
+    assert(vreg->neighbours == 0);
     {
         struct neighbour_iterator nit = {};
         while (graph_next_neighbour(&interference, vreg, &nit))
         {
             struct vreg* neighbour = nit.data;
-            bitmap_set(&neighbour->bitmap, 32, vreg->hreg);
+            array_push(&simplified, neighbour);
+            vreg->neighbours++;
         }
     }
+    array_push(&simplified, vreg);
 
     /* ...and remove it from the graph. */
 
@@ -241,6 +245,38 @@ static bool attempt_to_simplify(void)
     return true;
 }
 
+static bool attempt_to_freeze(void)
+{
+    struct vreg* vreg = NULL;
+    int degree = INT_MAX;
+
+    /* Find the affinity node with the lowest interference degree. */
+
+    {
+        struct vertex_iterator vit = {};
+        while (graph_next_vertex(&affinity, &vit))
+        {
+            struct vreg* v = vit.data;
+            int d = graph_get_vertex_degree(&interference, v);
+            if (d < degree)
+            {
+                vreg = v;
+                degree = d;
+            }
+        }
+    }
+
+    if (!vreg)
+        return false;
+
+    tracef('R', "R: freezing vreg %%%d with degree %d\n",
+        vreg->id, degree);
+
+    graph_remove_vertex(&affinity, vreg);
+
+    return true;
+}
+
 static bool attempt_to_spill(void)
 {
     struct vreg* vreg = NULL;
@@ -280,7 +316,6 @@ static bool attempt_to_spill(void)
     return true;
 }
 
-
 static void iterate(void)
 {
     struct anode* spill;
@@ -296,20 +331,45 @@ static void iterate(void)
         if (attempt_to_simplify())
             continue;
 
-        if (attempt_to_spill())
-             continue;
+        if (attempt_to_freeze())
+            continue;
+
+        // if (attempt_to_spill())
+        //      continue;
 
         fatal("unable to allocate registers!");
     }
 }
 
+static void assign_hard_registers(void)
+{
+    while (simplified.count > 0)
+    {
+        struct vreg* vreg = array_pop(&simplified);
+        int neighbours = vreg->neighbours;
+        unsigned int bitmap = 0;
+
+        while (neighbours > 0)
+        {
+            struct vreg* neighbour = actual(array_pop(&simplified));
+            if (neighbour->hreg != -1)
+                bitmap_set(&bitmap, 32, neighbour->hreg);
+            neighbours--;
+        }
+
+        vreg->hreg = bitmap_find_unset_bit(&bitmap, 32);
+    }
+}
+
 void pass_register_allocator(void)
 {
     wire_together_bbs();
     generate_graph();
 
     dump_interference_graph();
+    simplified.count = 0;
     iterate();
+    assign_hard_registers();
 
     graph_reset(&interference);
     graph_reset(&affinity);
diff --git a/mach/proto/mcg/reg.h b/mach/proto/mcg/reg.h
index cc5868dfa..1e04c6298 100644
--- a/mach/proto/mcg/reg.h
+++ b/mach/proto/mcg/reg.h
@@ -19,7 +19,7 @@ struct vreg
     struct value* value;
     struct vreg* coalesced_with;
     int hreg;
-    unsigned int bitmap;
+    int neighbours;
     bool needs_register;
     bool is_spilt;
 };