[Bug middle-end/46679] fold_binary changes types in divisionm breaking configure -enable-checking

[jay.krell at cornell dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46679

Jay <jay.krell at cornell dot edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|4.5.1                       |4.6.0

--- Comment #1 from Jay <jay.krell at cornell dot edu> 2010-12-02 09:08:49 UTC ---
You can "prove", almost, the existance of the bug by
making this change to slightly increase it:

jbook2:gcc jay$ svn diff  fold-const.c 
Index: fold-const.c
===================================================================
--- fold-const.c    (revision 167194)
+++ fold-const.c    (working copy)
@@ -11648,7 +11648,7 @@
      Note that only CEIL_DIV_EXPR and FLOOR_DIV_EXPR are rewritten now.
      At one time others generated faster code, it's not clear if they do
      after the last round to changes to the DIV code in expmed.c.  */
-      if ((code == CEIL_DIV_EXPR || code == FLOOR_DIV_EXPR)
+      if ((code == CEIL_DIV_EXPR || code == TRUNC_DIV_EXPR || code ==
FLOOR_DIV_EXPR)
       && multiple_of_p (type, arg0, arg1))
     return fold_build2_loc (loc, EXACT_DIV_EXPR, type, arg0, arg1);


it: I don't think C ever produces ceil_div/floor_div, so
it's hard to demonstrate.

With this, bootstrap fails:


/src/gcc-trunk/configure -prefix=/usr/local/gcc-trunk
-enable-checking=assert,df,fold,misc,rtl,rtlflag,runtime,tree,types && make -j4

/src/gcc-trunk/gcc/tree-ssa-loop-prefetch.c:1503:1: error: type mismatch in
binary expression
unsigned int
int
unsigned int
D.55547 = D.55546 /[ex] 16;

other than just removing this chunk of code completely,
I might suggest checking that arg0 == op0 && arg1 == op1.
Though that is probably a bit more conservative than necessary.