From: David Given <dg@cowlark.com>
Date: Tue, 4 Oct 2016 21:42:00 +0000 (+0200)
Subject: Add a pass to do critical edge splitting.
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=ac62c34e1975c56055af20a1ee4d42455ece3bde;p=ack.git

Add a pass to do critical edge splitting.
---

diff --git a/mach/proto/mcg/mcg.h b/mach/proto/mcg/mcg.h
index a5fa1102c..dc70028c9 100644
--- a/mach/proto/mcg/mcg.h
+++ b/mach/proto/mcg/mcg.h
@@ -100,13 +100,14 @@ extern void tb_fileend(void);
 extern void tb_procedure(struct procedure* proc);
 extern void tb_regvar(struct procedure* proc, arith offset, int size, int type, int priority);
 
+extern void pass_convert_locals_to_ssa(struct procedure* proc);
 extern void pass_convert_stack_ops(struct procedure* proc);
-extern void pass_remove_dead_blocks(struct procedure* proc);
 extern void pass_eliminate_trivial_blocks(struct procedure* proc);
+extern void pass_group_irs(struct procedure* proc);
 extern void pass_instruction_selector(struct procedure* proc);
 extern void pass_promote_float_ops(struct procedure* proc);
-extern void pass_group_irs(struct procedure* proc);
-extern void pass_convert_locals_to_ssa(struct procedure* proc);
+extern void pass_remove_dead_blocks(struct procedure* proc);
+extern void pass_split_critical_edges(struct procedure* proc);
 
 #endif
 
diff --git a/mach/proto/mcg/pass_splitcriticaledges.c b/mach/proto/mcg/pass_splitcriticaledges.c
new file mode 100644
index 000000000..a7fa63ee9
--- /dev/null
+++ b/mach/proto/mcg/pass_splitcriticaledges.c
@@ -0,0 +1,91 @@
+#include "mcg.h"
+
+/* Insert empty nodes at certain places in the basic block graph so that when
+ * we convert out of SSA form, we have somewhere to insert copies. This is
+ * necessary for correctness in certain circumstances. The best explanation of
+ * why I've found is here, starting at the bottom of page 23.
+ *
+ * Briggs, Preston, et al.
+ * "Practical improvements to the construction and destruction of static single assignment form."
+ * Software-Practice and experience 28.8 (1998): 859-882.
+ *
+ * http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.25.749
+ */
+
+static struct procedure* current_proc;
+
+struct rewrite_params
+{
+	struct basicblock* find;
+	struct basicblock* replace;
+};
+
+static bool find_replace_cb(struct ir* ir, void* user)
+{
+	struct rewrite_params* rwp = user;
+
+	if ((ir->opcode == IR_BLOCK) && (ir->u.bvalue == rwp->find))
+		ir->u.bvalue = rwp->replace;
+	
+	return false;
+}
+
+static void split_edge(struct basicblock* source, struct basicblock* sink)
+{
+	int i;
+	struct rewrite_params rwp;
+	struct basicblock* bb = bb_get(NULL);
+	
+	array_append(&bb->irs,
+		new_ir1(
+			IR_JUMP, 0,
+			new_bbir(sink)
+		)
+	);
+
+	rwp.find = sink;
+	rwp.replace = bb;
+
+	for (i=0; i<source->irs.count; i++)
+		ir_walk(source->irs.item[i], find_replace_cb, &rwp);
+
+	array_remove(&source->nexts, sink);
+	array_append(&source->nexts, bb);
+
+	array_append(&bb->prevs, source);
+	array_append(&bb->nexts, sink);
+
+	array_remove(&sink->prevs, source);
+	array_append(&sink->prevs, bb);
+
+	array_append(&current_proc->blocks, bb);
+}
+
+static void consider_edges_leading_to(struct basicblock* bb)
+{
+	if (bb->prevs.count > 1)
+	{
+		int i;
+
+		for (i=0; i<bb->prevs.count; i++)
+		{
+			struct basicblock* prev = bb->prevs.item[i];
+			if (prev->nexts.count > 1)
+				split_edge(prev, bb);
+		}
+	}
+}
+
+void pass_split_critical_edges(struct procedure* proc)
+{
+	int i;
+
+	current_proc = proc;
+
+    for (i=0; i<proc->blocks.count; i++)
+		consider_edges_leading_to(proc->blocks.item[i]);
+}
+
+/* vim: set sw=4 ts=4 expandtab : */
+
+
diff --git a/mach/proto/mcg/procedure.c b/mach/proto/mcg/procedure.c
index 5ea0372b9..8fbccd5d6 100644
--- a/mach/proto/mcg/procedure.c
+++ b/mach/proto/mcg/procedure.c
@@ -15,7 +15,23 @@ static void print_blocks(char k, struct procedure* proc)
             bb->is_fake ? "FAKE " : "",
             bb->name);
 
-		for (int j=0; j<bb->irs.count; j++)
+        if (bb->prevs.count > 0)
+        {
+            tracef(k, "%c: FROM:", k);
+            for (j=0; j<bb->prevs.count; j++)
+                tracef(k, " %s", bb->prevs.item[j]->name);
+            tracef(k, "\n");
+        }
+
+        if (bb->nexts.count > 0)
+        {
+            tracef(k, "%c:   TO:", k);
+            for (j=0; j<bb->nexts.count; j++)
+                tracef(k, " %s", bb->nexts.item[j]->name);
+            tracef(k, "\n");
+        }
+
+		for (j=0; j<bb->irs.count; j++)
 			ir_print(k, bb->irs.item[j]);
 	}
 }
@@ -40,8 +56,10 @@ void procedure_compile(struct procedure* proc)
     print_blocks('3', proc);
     pass_convert_locals_to_ssa(proc);
     print_blocks('4', proc);
-    pass_promote_float_ops(proc);
+    pass_split_critical_edges(proc);
     print_blocks('5', proc);
+    pass_promote_float_ops(proc);
+    print_blocks('6', proc);
 
 
     pass_instruction_selector(proc);