Add tree_fits_uhwi_p tests to BIT_FIELD_REF folder

[Richard Sandiford]

The first BIT_FIELD_REF folding pattern assumed without checking that
operands satisfy tree_fits_uhwi_p.  The second pattern does check this:

      /* On constants we can use native encode/interpret to constant
         fold (nearly) all BIT_FIELD_REFs.  */
      if (CONSTANT_CLASS_P (arg0)
          && can_native_interpret_type_p (type)
          && BITS_PER_UNIT == 8
          && tree_fits_uhwi_p (op1)
          && tree_fits_uhwi_p (op2))

so this patch adds the checks to the first pattern too.  This is needed
for POLY_INT_CST bit positions.

Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linux-gnu.
Also tested by comparing the before and after assembly output for at
least one target per CPU directory.  OK to install?

Richard


2018-01-04  Richard Sandiford  <richard.sandif...@linaro.org>

gcc/
        * fold-const.c (fold_ternary_loc): Check tree_fits_uhwi_p before
        using tree_to_uhwi.

Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c    2018-01-03 21:42:34.349039784 +0000
+++ gcc/fold-const.c    2018-01-04 10:06:02.165809202 +0000
@@ -11643,7 +11643,9 @@ fold_ternary_loc (location_t loc, enum t
       if (TREE_CODE (arg0) == VECTOR_CST
          && (type == TREE_TYPE (TREE_TYPE (arg0))
              || (TREE_CODE (type) == VECTOR_TYPE
-                 && TREE_TYPE (type) == TREE_TYPE (TREE_TYPE (arg0)))))
+                 && TREE_TYPE (type) == TREE_TYPE (TREE_TYPE (arg0))))
+         && tree_fits_uhwi_p (op1)
+         && tree_fits_uhwi_p (op2))
        {
          tree eltype = TREE_TYPE (TREE_TYPE (arg0));
          unsigned HOST_WIDE_INT width = tree_to_uhwi (TYPE_SIZE (eltype));