arm: remove incorrect handling of FP bignums in move_or_literal_pool

This hunk of code in move_or_literal_pool just looks wrong, but I
can't find a testcase that will tickle it to prove it.  It looks a bit
like it was intended to catch cases where a bignum contained a
floating-point value, but there were a number of problems with it.

- It tested X_add_number == -1, but an FP bignum is indicated by any
  value <= 0.
- It converted the floating-point value to extended precision, but
  that's not used on Arm beyond the legacy FPA code.  No attempt was
  made to match the FP value to the intended memory/mov operation.

Since I can't construct a viable testcase, I've just removed the existing
code and made the function error out in this case: this seems more sensible
than generating wrong code or trying to write something more complex that
can't be tested anyway.

diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 343b2e77d7c2d7610a846d918b9344b87dc98c95..41bcfb8dee2d8669e85ad74250ee1dbfe3a9de6c 100644 (file)
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -8922,14 +8922,32 @@ move_or_literal_pool (int i, enum lit_type t, bool mode_3)
       uint64_t v;
       if (inst.relocs[0].exp.X_op == O_big)
        {
-         LITTLENUM_TYPE w[X_PRECISION];
-         LITTLENUM_TYPE * l;
+         LITTLENUM_TYPE *l;
 
-         if (inst.relocs[0].exp.X_add_number == -1)
+         if (inst.relocs[0].exp.X_add_number <= 0)  /* FP value.  */
            {
-             gen_to_words (w, X_PRECISION, E_PRECISION);
-             l = w;
-             /* FIXME: Should we check words w[2..5] ?  */
+             /* FIXME: The code that was here previously could not
+                work.  Firstly, it tried to convert a floating point
+                number into an extended precision format, but only
+                provided a buffer of 5 littlenums, which was too
+                small.  Secondly, it then didn't deal with the value
+                converted correctly, just reading out the first 4
+                littlenum fields and assuming that could be used
+                directly.
+
+                I think the code was intended to handle expressions
+                such as:
+
+                       LDR r0, =1.0
+                       VLDR d0, =55.3
+
+                but the parsers currently don't permit floating-point
+                literal values to be written this way, so this code
+                is probably unreachable.  To be safe, we simply
+                return an error here.  */
+
+             inst.error = _("constant expression not supported");
+             return true;
            }
          else
            l = generic_bignum;