From 4e2a72cc6b48005a65e199feaae9957aa89ef991 Mon Sep 17 00:00:00 2001
From: Rhys Weatherley <rweather@southern-storm.com.au>
Date: Wed, 26 May 2004 01:19:38 +0000
Subject: [PATCH] Add "jit_block_current_is_dead" to simplify testing if the
 last block is reachable or not, taking empty trailing blocks into account.

---
 ChangeLog               |  5 +++++
 dpas/dpas-parser.y      |  3 +--
 include/jit/jit-block.h |  1 +
 jit/jit-block.c         | 36 ++++++++++++++++++++++++++++++++++++
 jit/jit-insn.c          | 24 ++----------------------
 5 files changed, 45 insertions(+), 24 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 81b186a..f3b4dc5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,11 @@
 	jitplus/jit-plus-function.cpp: add "jit_insn_new_block" to simplify
 	creating a new block that doesn't have an explicit label.
 
+	* dpas/dpas-parser.y, include/jit/jit-block.h, jit/jit-block.c,
+	jit/jit-insn.c: add "jit_block_current_is_dead" to simplify
+	testing if the last block is reachable or not, taking empty
+	trailing blocks into account.
+
 2004-05-25  Rhys Weatherley  <rweather@southern-storm.com.au>
 
 	* tools/.cvsignore, tools/Makefile.am, tools/gen-sel-parser.y,
diff --git a/dpas/dpas-parser.y b/dpas/dpas-parser.y
index 426b7a0..0242db4 100644
--- a/dpas/dpas-parser.y
+++ b/dpas/dpas-parser.y
@@ -1787,8 +1787,7 @@ IfTail
 				jit_label_t label = jit_label_undefined;
 
 				/* Jump to the end of the "if" statement */
-				if(!jit_block_ends_in_dead
-						(jit_block_previous(dpas_current_function(), 0)))
+				if(!jit_block_current_is_dead(dpas_current_function()))
 				{
 					if(!jit_insn_branch(dpas_current_function(), &label))
 					{
diff --git a/include/jit/jit-block.h b/include/jit/jit-block.h
index b4a5295..30aeca6 100644
--- a/include/jit/jit-block.h
+++ b/include/jit/jit-block.h
@@ -42,6 +42,7 @@ void *jit_block_get_meta(jit_block_t block, int type) JIT_NOTHROW;
 void jit_block_free_meta(jit_block_t block, int type) JIT_NOTHROW;
 int jit_block_is_reachable(jit_block_t block) JIT_NOTHROW;
 int jit_block_ends_in_dead(jit_block_t block) JIT_NOTHROW;
+int jit_block_current_is_dead(jit_function_t func) JIT_NOTHROW;
 
 #ifdef	__cplusplus
 };
diff --git a/jit/jit-block.c b/jit/jit-block.c
index ae9cb90..8123f98 100644
--- a/jit/jit-block.c
+++ b/jit/jit-block.c
@@ -369,6 +369,42 @@ int jit_block_ends_in_dead(jit_block_t block)
 	return block->ends_in_dead;
 }
 
+/*@
+ * @deftypefun int jit_block_current_is_dead (jit_function_t func)
+ * Determine if the current point in the function is dead.  That is,
+ * there are no existing branches or fall-throughs to this point.
+ * This differs slightly from @code{jit_block_ends_in_dead} in that
+ * this can skip past zero-length blocks that may not appear to be
+ * dead to find the dead block at the head of a chain of empty blocks.
+ * @end deftypefun
+@*/
+int jit_block_current_is_dead(jit_function_t func)
+{
+	jit_block_t block = jit_block_previous(func, 0);
+	while(block != 0)
+	{
+		if(block->ends_in_dead)
+		{
+			return 1;
+		}
+		else if(!(block->entered_via_top) &&
+				!(block->entered_via_branch))
+		{
+			return 1;
+		}
+		else if(block->entered_via_branch)
+		{
+			break;
+		}
+		else if(block->first_insn <= block->last_insn)
+		{
+			break;
+		}
+		block = block->prev;
+	}
+	return 0;
+}
+
 /*
  * Determine if a block is empty or is never entered.
  */
diff --git a/jit/jit-insn.c b/jit/jit-insn.c
index a103b3a..457c609 100644
--- a/jit/jit-insn.c
+++ b/jit/jit-insn.c
@@ -6084,8 +6084,6 @@ int jit_insn_return_ptr
 @*/
 int jit_insn_default_return(jit_function_t func)
 {
-	jit_block_t current;
-
 	/* Ensure that we have a builder for this function */
 	if(!_jit_function_ensure_builder(func))
 	{
@@ -6094,27 +6092,9 @@ int jit_insn_default_return(jit_function_t func)
 
 	/* If the last block ends in an unconditional branch, or is dead,
 	   then we don't need to add a default return */
-	current = func->builder->current_block;
-	while(current != 0)
+	if(jit_block_current_is_dead(func))
 	{
-		if(current->ends_in_dead)
-		{
-			return 2;
-		}
-		else if(!(current->entered_via_top) &&
-				!(current->entered_via_branch))
-		{
-			return 2;
-		}
-		else if(current->entered_via_branch)
-		{
-			break;
-		}
-		else if(current->first_insn <= current->last_insn)
-		{
-			break;
-		}
-		current = current->prev;
+		return 2;
 	}
 
 	/* Add a simple "void" return to terminate the function */
-- 
2.47.3