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Re: [rfc] multi-word subreg lowering pass
- From: Martin Koegler <mkoegler at auto dot tuwien dot ac dot at>
- To: rth at redhat dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Mon, 27 Jun 2005 09:33:35 +0200
- Subject: Re: [rfc] multi-word subreg lowering pass
On Sat, 7 May 2005 18:35:51 -0700, Richard Henderson wrote:
> For AND, IOR, XOR, you should be able to delete the multi-word patterns
> entirely, and leave those operations to be generated by the middle-end.
This will not work for the current CVS version, which requires operations for
mode_for_size(sizeof(int),MODE_INT,0) mode is present (at least for xor).
long long foo (double x, double y)
return !__builtin_isunordered (x, y);
If it compiled (without any optimizations), the gimple form is:
foo (x, y)
long long int D.1390;
D.1391 = x unord y;
D.1392 = !D.1391;
D.1390 = (long long int) D.1392;
sizeof(_Bool) is 1 for most architectures. expand_binop for D.1392 =
!D.1391 will be called with a QI Register and (CONST_INT 1) as operands and a result
register with mode_for_size(sizeof(int),MODE_INT,0) mode.
On i386, the result will be a SI register. As xor for SI mode is available,
the following case will be used:
if (methods != OPTAB_MUST_WIDEN
&& binoptab->handlers[(int) mode].insn_code != CODE_FOR_nothing)
In this case, the QI operands are converted to the right mode.
On AVR, word_mode is 1, while sizeof(int) is 2 (unless an option is
specified). Therefore the result will be a HI register. If xor would
only be available for QI mode, the following case will be used:
/* These can be done a word at a time. */
if ((binoptab == and_optab || binoptab == ior_optab || binoptab == xor_optab)
&& class == MODE_INT
&& GET_MODE_SIZE (mode) > UNITS_PER_WORD
&& binoptab->handlers[(int) word_mode].insn_code != CODE_FOR_nothing)
Here operand_subword_force will be called for a QI operand (with
mode=HI as parameter), which will cause an internal compiler error.
mfg Martin Kögler