In combine, simplify_comparison() is being called with the following
arguments:
code = EQ
op0 = (and:SI (mem:SI (reg/v/f:SI 50 [ gp ]) (const_int 4 [0x4]))
op1 = (const_int 0 [0])
After churning down through make_compound_operation() and
make_compound_operation_int(), processing gets to make_extraction().
Eventually (combine.c:7753), make_extract() decides that the best
pattern is EP_epextzv. No instruction patterns are provided for
"extz*"; get_best_reg_extraction_insn() returns false, and
make_extraction falls through to this code [indenting modified for
email].
combine.c:7786:
/* Be careful not to go beyond the extracted object and
maintain the natural alignment of the memory. */
wanted_inner_mode = smallest_int_mode_for_size (len);
while (pos % GET_MODE_BITSIZE (wanted_inner_mode) + len
> GET_MODE_BITSIZE (wanted_inner_mode))
wanted_inner_mode = GET_MODE_WIDER_MODE
(wanted_inner_mode).require ();
Len == 1; the result is that wanted_inner_mode == E_QImode.
No instruction patterns are provided for "extz*";
get_best_reg_extraction_insn() returns false, and make_extraction falls
through to this code
The (mem:SI) is converted to (mem:QI).
The return from make_extract() is
(zero_extract:SI (mem:QI (reg/v/f:SI 50 [ gp ]))
(const_int 1 [0x1])
(const_int 2 [0x2]))
The target has an instruction pattern for zero_extract, but it matches
SI values, not QI. So the instruction which implements a test of a bit
flag is never generated.
In an old version of GCC, a call to mode_dependent_address_p()
controlled whether this conversion from SI to QI was done. This would
not be useful, since QI is a valid address mode in general, just not for
the zero_extract pattern. A kludge was added to prevent this conversion
from SI to QI. I'd like to avoid re-implementing the kludge.
Questions:
1. What is make_extract() trying to do with the MEM address?
2. Why modify the MEM address from SI to QI?
There's no obvious benefit that I see of
(zero_extract:SI (mem:QI)...) over (zero_extract:SI (mem:SI)...).
3. What's the best way to fix this?
- Remove the down-sizing of MEM in make_extract()?
- Define patterns for extz*?
- Do something so zero_extend accepts QI?
--
Michael Eager ea...@eagerm.com
1960 Park Blvd., Palo Alto, CA 94306
