| Message ID | 1629803.uCIxAQNden@polaris |
|---|---|
| State | New |
| Headers | show |
On Mon, Feb 17, 2014 at 11:27 AM, Eric Botcazou <ebotcazou@adacore.com> wrote: >> There is nothing obvious I think, i.e. that's debatable. I agree that a VCE >> from a 32-bit object to a 32-bit integer with 24-bit precision should not >> clear the upper 8 bits (so the REDUCE_BIT_FIELD part of my patch is wrong). >> But here we have a VCE from a 24-bit object to a 32-bit integer with 24-bit >> precision which reads *more bits* than the size of the source type; that I >> think is plain wrong and is fixed by the bit-field extraction in the patch. > > Revised patch along these lines attached. Although I agree that it's a bit of > a kludge, it's quite localized and plausible IMO. Woudln't it be better to do this in the series of "conversions", that is inside the preceeding if-statement? (the integral type case using convert_modes looks weird enough, so adding this kind-of "less" weird one there looks sensible) Ok with moving it there (before the else if (!MEM_P (op0))). You probably want to guard with INTEGRAL_TYPE_P (type) as well, not only GET_MODE (op0) != mode - just to prepare for weird stuff like a vector-type where TYPE_PRECISION means sth else. Thanks, Richard. > > * expr.c (expand_expr_real_1) <case VIEW_CONVERT_EXPR>: For a bit-field > destination type, extract exactly the number of valid bits if the source > type isn't integral or has a different precision. > > > -- > Eric Botcazou
Index: expr.c =================================================================== --- expr.c (revision 207796) +++ expr.c (working copy) @@ -10458,15 +10458,21 @@ expand_expr_real_1 (tree exp, rtx target op0 = target; } - /* At this point, OP0 is in the correct mode. If the output type is + /* If OP0 is a MEM without the correct mode and we need to reduce it to + a bit-field type, do an extraction. Otherwise, we can read all bits + of MODE but need to deal with the alignment. If the output type is such that the operand is known to be aligned, indicate that it is. - Otherwise, we need only be concerned about alignment for non-BLKmode - results. */ + Otherwise, we actually need only be concerned about alignment for + non-BLKmode results. */ if (MEM_P (op0)) { enum insn_code icode; - if (TYPE_ALIGN_OK (type)) + if (reduce_bit_field && GET_MODE (op0) != mode) + return extract_bit_field (op0, TYPE_PRECISION (type), 0, + TYPE_UNSIGNED (type), NULL_RTX, + mode, mode); + else if (TYPE_ALIGN_OK (type)) { /* ??? Copying the MEM without substantially changing it might run afoul of the code handling volatile memory references in