* function.c (gen_mem_addressof): If the address REG is

	REG_USERVAR_P make the new REG be so also.
	* loop.c (scan_loop): Apply DeMorgan's laws and add documentation
	in an attempt to clarify slightly.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@22667 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 25 insertions, 13 deletions

diff --git a/gcc/loop.c b/gcc/loop.c
index f1a59b35f8d..0a6cf059b44 100644
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -871,19 +871,31 @@ scan_loop (loop_start, end, unroll_p, bct_p)
 	     We don't know its life-span, so we can't compute the benefit.  */
 	  if (REGNO (SET_DEST (set)) >= max_reg_before_loop)
 	    ;
-	  /* In order to move a register, we need to have one of three cases:
-	     (1) it is used only in the same basic block as the set
-	     (2) it is not a user variable and it is not used in the
-	         exit test (this can cause the variable to be used
-		 before it is set just like a user-variable).
-	     (3) the set is guaranteed to be executed once the loop starts,
-	         and the reg is not used until after that.  */
-	  else if (! ((! maybe_never
-		       && ! loop_reg_used_before_p (set, p, loop_start,
-						    scan_start, end))
-		      || (! REG_USERVAR_P (SET_DEST (set))
-			  && ! REG_LOOP_TEST_P (SET_DEST (set)))
-		      || reg_in_basic_block_p (p, SET_DEST (set))))
+	  else if (/* The set is a user-variable or it is used in
+		      the exit test (this can cause the variable to be
+		      used before it is set just like a
+		      user-variable)...  */
+		   (REG_USERVAR_P (SET_DEST (set))
+		    || REG_LOOP_TEST_P (SET_DEST (set)))
+		   /* And the set is not guaranteed to be executed one
+		      the loop starts, or the value before the set is
+		      needed before the set occurs... */
+		   && (maybe_never
+		       || loop_reg_used_before_p (set, p, loop_start,
+						  scan_start, end))
+		   /* And the register is used in basic blocks other
+		      than the one where it is set (meaning that
+		      something after this point in the loop might
+		      depend on its value before the set).  */
+		   && !reg_in_basic_block_p (p, SET_DEST (set)))
+	    /* It is unsafe to move the set.  The fact that these
+	       three conditions are considered in conjunction means
+	       that we are assuming various conditions, such as:
+
+	         o It's OK to move a set of a variable which was not
+	           created by the user and is not used in an exit test
+	           even if that point in the set would not be reached
+		   during execution of the loop.  */
 	    ;
 	  else if ((tem = invariant_p (src))
 		   && (dependencies == 0