Backport the fix for PR51799

Created attachment 26281
Failing test case.

The attached test case causes the compiler to ICE as follows:

$ arm-none-eabi-gcc -O1 -ftree-vectorize -mcpu=cortex-a9 \
      -mfpu=neon -mfloat-abi=softfp ice.c
ice.c: In function 'f0a':
ice.c:7:1: internal compiler error: in vect_is_simple_use_1, at tree-vect-stmts.c:5987
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

Checked against trunk revision 183018.

Did it work with 4.6.x? If so, please mark it as regression.

Doesn't ICE with GCC 4.6.2.

Thanks for checking.

This is actually the same problem as in pr 51301, and the fix of 51301 looks incomplete: we want an over-promoted sequence to end with type demotion operation, so we need to check that properly:

Index: tree-vect-patterns.c
===================================================================
--- tree-vect-patterns.c (revision 182840)
+++ tree-vect-patterns.c (working copy)
@@ -1186,13 +1186,15 @@
     {
       use_lhs = gimple_assign_lhs (use_stmt);
       use_type = TREE_TYPE (use_lhs);
- /* Support only type promotion or signedess change. Check that USE_TYPE
- is not bigger than the original type. */
+ /* Support only type demotion or signedess change. */
       if (!INTEGRAL_TYPE_P (use_type)
- || TYPE_PRECISION (new_type) > TYPE_PRECISION (use_type)
- || TYPE_PRECISION (type) < TYPE_PRECISION (use_type))
+ || TYPE_PRECISION (type) <= TYPE_PRECISION (use_type))
         return NULL;

+ /* Check that NEW_TYPE is not bigger than the conversion result. */
+ if (TYPE_PRECISION (new_type) > TYPE_PRECISION (use_type))
+ return NULL;
+
       if (TYPE_UNSIGNED (new_type) != TYPE_UNSIGNED (use_type)
           || TYPE_PRECISION (new_type) != TYPE_PRECISION (use_type))
         {

I am going to test this patch.

Author: irar
Date: Thu Jan 12 14:41:44 2012
New Revision: 183126

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=183126
Log:

        PR tree-optimization/51799
        * tree-vect-patterns.c (vect_recog_over_widening_pattern): Check
        that the last operation is a type demotion.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr51799.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/vect/vect-widen-shift-u8.c
    trunk/gcc/tree-vect-patterns.c

Fixed.