X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=ir%2Fopt%2Fjumpthreading.c;h=39de745f4dfad750b0b98f6d122a327ab193af37;hb=5ea61f3166daab45e560f0d7955fd4c72d8c7167;hp=8e6f9fa92c3a484feb3fd82fdd6f941bcc2f3166;hpb=d304e6e0053ecf1de3f541121ee70d7542bf9f84;p=libfirm

diff --git a/ir/opt/jumpthreading.c b/ir/opt/jumpthreading.c
index 8e6f9fa92..39de745f4 100644
--- a/ir/opt/jumpthreading.c
+++ b/ir/opt/jumpthreading.c
@@ -60,7 +60,7 @@ static void add_pred(ir_node* node, ir_node* x)
 	int n;
 	int i;
 
-	assert(is_Block(node) || is_Phi(node));
+	assert(is_Block(node));
 
 	n = get_irn_arity(node);
 	NEW_ARR_A(ir_node*, ins, n + 1);
@@ -194,6 +194,16 @@ static void construct_ssa(ir_node *orig_block, ir_node *orig_val,
 	}
 }
 
+/**
+ * jumpthreading produces critical edges, e.g. B-C:
+ *     A         A
+ *  \ /       \  |
+ *   B    =>   B |
+ *  / \       / \|
+ *     C         C
+ *
+ * By splitting this critical edge more threadings might be possible.
+ */
 static void split_critical_edge(ir_node *block, int pos)
 {
 	ir_graph *irg = get_irn_irg(block);
@@ -634,6 +644,7 @@ static void thread_jumps(ir_node* block, void* data)
 	ir_node *badX;
 	int      cnst_pos;
 
+	/* we do not deal with Phis, so restrict this to exactly one cfgpred */
 	if (get_Block_n_cfgpreds(block) != 1)
 		return;
 
@@ -716,6 +727,10 @@ static void thread_jumps(ir_node* block, void* data)
 	if (copy_block == NULL)
 		return;
 
+	/* We might thread the condition block of an infinite loop,
+	 * such that there is no path to End anymore. */
+	keep_alive(block);
+
 	/* we have to remove the edge towards the pred as the pred now
 	 * jumps into the true_block. We also have to shorten Phis
 	 * in our block because of this */