* doc/invoke.texi: Document max-jump-thread-duplication-stmts PARAM.

	* tree-ssa-dom.c: Include params.h.
	(thread_across_edge): If there are too many statements in the
	target block, then do not thread through it.
	* Makefile.in (tree-ssa-dom.o): Depend on $(PARAMS_H).
	* params.def (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS): New PARAM.

	



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@106503 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 18 insertions, 0 deletions

diff --git a/gcc/params.def b/gcc/params.def
index f808682a06f..f0740a9d00f 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -506,6 +506,24 @@ DEFPARAM (PARAM_SSP_BUFFER_SIZE,
 	  "The lower bound for a buffer to be considered for stack smashing protection",
 	  8, 1, 0)
 
+/* When we thread through a block we have to make copies of the
+   statements within the block.  Clearly for large blocks the code
+   duplication is bad.
+
+   PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS specifies the maximum number
+   of statements and PHI nodes allowed in a block which is going to
+   be duplicated for thread jumping purposes.
+
+   Some simple analysis showed that more than 99% of the jump
+   threading opportunities are for blocks with less than 15
+   statements.  So we can get the benefits of jump threading
+   without excessive code bloat for pathological cases with the
+   throttle set at 15 statements.  */
+DEFPARAM (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS,
+	  "max-jump-thread-duplication-stmts",
+          "Maximum number of statements allowed in a block that needs to be duplicated when threading jumps",
+	  15, 0, 0)
+   
 /*
 Local variables:
 mode:c