X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=ir%2Fbe%2Fbeemitter_binary.c;h=f80246f8fe0432a045ac6e21339f30bec0516b0c;hb=e0e9e9ace61d3ec46e4d09c7ab2c6947b17b2778;hp=57650784a7d899139212053b9167d4b349916237;hpb=a4f4c0eec98741b870064f189492455814ebe53e;p=libfirm

diff --git a/ir/be/beemitter_binary.c b/ir/be/beemitter_binary.c
index 57650784a..f80246f8f 100644
--- a/ir/be/beemitter_binary.c
+++ b/ir/be/beemitter_binary.c
@@ -43,8 +43,8 @@ struct obstack code_fragment_obst;
     be_emit(8/16/32/entity) call!) */
 code_fragment_t *be_get_current_fragment(void)
 {
-	assert(obstack_object_size(&code_fragment_obst) >= sizeof(code_fragment_t));
 	code_fragment_t *fragment = obstack_base(&code_fragment_obst);
+	assert(obstack_object_size(&code_fragment_obst) >= sizeof(code_fragment_t));
 	assert(fragment->magic == CODE_FRAGMENT_MAGIC);
 
 	return fragment;
@@ -121,7 +121,8 @@ static unsigned align(unsigned offset, unsigned alignment)
 	return offset;
 }
 
-static bool determine_jumpsize_pass(const binary_emiter_interface_t *interface)
+static bool determine_jumpsize_iteration(
+		const binary_emiter_interface_t *interface)
 {
 	unsigned         offset     = 0;
 	unsigned         max_offset = 0;
@@ -137,7 +138,7 @@ static bool determine_jumpsize_pass(const binary_emiter_interface_t *interface)
 	    max_offset = align(max_offset, alignment);
 
 		if (offset != fragment->offset) {
-			changed = true;
+			changed          = true;
 			fragment->offset = offset;
 		}
 	    fragment->max_offset = max_offset;
@@ -161,9 +162,14 @@ static void determine_offsets(const binary_emiter_interface_t *interface)
 	first_fragment->offset     = 0;
 	first_fragment->max_offset = 0;
 
-	/* pass1: encode minimum/maximum offsets into fragments */
+	/* The algorithm calculates a lower and upper bound for the offset of each
+	 * fragment. With this information we can calculate a lower and upper bound
+	 * for the size of each jump instruction.
+	 * A single iteration updates the offset bounds for all fragments and jump
+	 * sizes for each fragment. We iterate until we had an iteration where
+	 * none of the minimum offsets changed. */
 	do {
-		changed = determine_jumpsize_pass(interface);
+		changed = determine_jumpsize_iteration(interface);
 		/* TODO: we should have an abort mode for the case when the offsets
 		   don't converge fast enough. We could simply use a pessimistic
 		   solution after a few iterations... */
@@ -186,10 +192,11 @@ void be_emit_code(FILE *output, const binary_emiter_interface_t *interface)
 	for (fragment = first_fragment; fragment != NULL;
 	     fragment = fragment->next) {
 	    unsigned char *jmpbuffer;
+		unsigned nops;
 
 	    /* assure alignment by emitting nops */
 	    assert(fragment->offset >= offset);
-	    unsigned nops = fragment->offset - offset;
+	    nops = fragment->offset - offset;
 	    if (nops > 0) {
 	    	unsigned char *nopbuffer = obstack_alloc(&code_fragment_obst, nops);
 	    	interface->create_nops(nopbuffer, nops);