On Mon, Nov 4, 2013 at 3:34 AM, H.J. Lu <hjl.to...@gmail.com> wrote:
> Y
> On Mon, Nov 4, 2013 at 3:11 AM, Richard Sandiford
> <rsand...@linux.vnet.ibm.com> wrote:
>> "H.J. Lu" <hongjiu...@intel.com> writes:
>>> emit_block_move_via_movmem and set_storage_via_setmem have
>>>
>>> for (mode = GET_CLASS_NARROWEST_MODE (MODE_INT); mode != VOIDmode;
>>> mode = GET_MODE_WIDER_MODE (mode))
>>> {
>>> enum insn_code code = direct_optab_handler (movmem_optab, mode);
>>>
>>> if (code != CODE_FOR_nothing
>>> /* We don't need MODE to be narrower than BITS_PER_HOST_WIDE_INT
>>> here because if SIZE is less than the mode mask, as it is
>>> returned by the macro, it will definitely be less than the
>>> actual mode mask. */
>>> && ((CONST_INT_P (size)
>>> && ((unsigned HOST_WIDE_INT) INTVAL (size)
>>> <= (GET_MODE_MASK (mode) >> 1)))
>>> || GET_MODE_BITSIZE (mode) >= BITS_PER_WORD))
>>> {
>>>
>>> Backend may assume mode of size in movmem and setmem expanders is no
>>> widder than Pmode since size is within the Pmode address space. X86
>>> backend expand_set_or_movmem_prologue_epilogue_by_misaligned has
>>>
>>> rtx saveddest = *destptr;
>>>
>>> gcc_assert (desired_align <= size);
>>> /* Align destptr up, place it to new register. */
>>> *destptr = expand_simple_binop (GET_MODE (*destptr), PLUS, *destptr,
>>> GEN_INT (prolog_size),
>>> NULL_RTX, 1, OPTAB_DIRECT);
>>> *destptr = expand_simple_binop (GET_MODE (*destptr), AND, *destptr,
>>> GEN_INT (-desired_align),
>>> *destptr, 1, OPTAB_DIRECT);
>>> /* See how many bytes we skipped. */
>>> saveddest = expand_simple_binop (GET_MODE (*destptr), MINUS,
>>> saveddest,
>>> *destptr,
>>> saveddest, 1, OPTAB_DIRECT);
>>> /* Adjust srcptr and count. */
>>> if (!issetmem)
>>> *srcptr = expand_simple_binop (GET_MODE (*srcptr), MINUS, *srcptr,
>>> saveddest,
>>> *srcptr, 1, OPTAB_DIRECT);
>>> *count = expand_simple_binop (GET_MODE (*count), PLUS, *count,
>>> saveddest, *count, 1, OPTAB_DIRECT);
>>>
>>> saveddest is a negative number in Pmode and *count is in word_mode. For
>>> x32, when Pmode is SImode and word_mode is DImode, saveddest + *count
>>> leads to overflow. We could fix it by using mode of saveddest to compute
>>> saveddest + *count. But it leads to extra conversions and other backends
>>> may run into the same problem. A better fix is to limit mode of size in
>>> movmem and setmem expanders to Pmode. It generates better and correct
>>> memcpy and memset for x32.
>>>
>>> There is also a typo in comments. It should be BITS_PER_WORD, not
>>> BITS_PER_HOST_WIDE_INT.
>>
>> I don't think it's a typo. It's explaining why we don't have to worry about:
>>
>> GET_MODE_BITSIZE (mode) > BITS_PER_HOST_WIDE_INT
>>
>> in the CONST_INT_P test (because in that case the GET_MODE_MASK macro
>> will be an all-1 HOST_WIDE_INT, even though that's narrower than the
>> real mask).
>
> Thanks for explanation.
>
>> I don't think the current comment covers the BITS_PER_WORD test at all.
>> AIUI it's there because the pattern is defined as taking a length of
>> at most word_mode, so we should stop once we reach it.
>
> I see.
>
>> FWIW, I agree Pmode makes more sense on face value. But shouldn't
>> we replace the BITS_PER_WORD test instead of adding to it? Having both
>> would only make a difference for Pmode > word_mode targets, which might
>> be able to handle full Pmode lengths.
>
> Do we ever have a target with Pmode is wider than
> word_mode? If not, we can check Pmode instead.
>
>> Either way, the md.texi documentation should be updated too.
>>
This is the updated patch with md.texi change. The testcase is the same.
Tested on x32. OK to install?
Thanks.
--
H.J.
---
gcc/
2013-11-04 H.J. Lu <hongjiu...@intel.com>
PR middle-end/58981
* doc/md.texi (@code{movmem@var{m}}): Specify Pmode as mode of
pattern, instead of word_mode.
* expr.c (emit_block_move_via_movmem): Don't use mode wider than
Pmode for size.
(set_storage_via_setmem): Likewise.
gcc/testsuite/
2013-11-04 H.J. Lu <hongjiu...@intel.com>
PR middle-end/58981
* gcc.dg/pr58981.c: New test.
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index ac10a0a..1e22b88 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -5291,12 +5291,13 @@ are the first two operands, and both are
@code{mem:BLK}s with an
address in mode @code{Pmode}.
The number of bytes to move is the third operand, in mode @var{m}.
-Usually, you specify @code{word_mode} for @var{m}. However, if you can
+Usually, you specify @code{Pmode} for @var{m}. However, if you can
generate better code knowing the range of valid lengths is smaller than
-those representable in a full word, you should provide a pattern with a
+those representable in a full Pmode pointer, you should provide
+a pattern with a
mode corresponding to the range of values you can handle efficiently
(e.g., @code{QImode} for values in the range 0--127; note we avoid numbers
-that appear negative) and also a pattern with @code{word_mode}.
+that appear negative) and also a pattern with @code{Pmode}.
The fourth operand is the known shared alignment of the source and
destination, in the form of a @code{const_int} rtx. Thus, if the
diff --git a/gcc/expr.c b/gcc/expr.c
index 551a660..8ef2870 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -1297,11 +1297,12 @@ emit_block_move_via_movmem (rtx x, rtx y, rtx
size, unsigned int align,
/* We don't need MODE to be narrower than BITS_PER_HOST_WIDE_INT
here because if SIZE is less than the mode mask, as it is
returned by the macro, it will definitely be less than the
- actual mode mask. */
+ actual mode mask. Since SIZE is within the Pmode address
+ space, we limit MODE to Pmode. */
&& ((CONST_INT_P (size)
&& ((unsigned HOST_WIDE_INT) INTVAL (size)
<= (GET_MODE_MASK (mode) >> 1)))
- || GET_MODE_BITSIZE (mode) >= BITS_PER_WORD))
+ || GET_MODE_BITSIZE (mode) >= GET_MODE_BITSIZE (Pmode)))
{
struct expand_operand ops[6];
unsigned int nops;
@@ -2879,14 +2880,15 @@ set_storage_via_setmem (rtx object, rtx size,
rtx val, unsigned int align,
enum insn_code code = direct_optab_handler (setmem_optab, mode);
if (code != CODE_FOR_nothing
- /* We don't need MODE to be narrower than
- BITS_PER_HOST_WIDE_INT here because if SIZE is less than
- the mode mask, as it is returned by the macro, it will
- definitely be less than the actual mode mask. */
+ /* We don't need MODE to be narrower than BITS_PER_HOST_WIDE_INT
+ here because if SIZE is less than the mode mask, as it is
+ returned by the macro, it will definitely be less than the
+ actual mode mask. Since SIZE is within the Pmode address
+ space, we limit MODE to Pmode. */
&& ((CONST_INT_P (size)
&& ((unsigned HOST_WIDE_INT) INTVAL (size)
<= (GET_MODE_MASK (mode) >> 1)))
- || GET_MODE_BITSIZE (mode) >= BITS_PER_WORD))
+ || GET_MODE_BITSIZE (mode) >= GET_MODE_BITSIZE (Pmode)))
{
struct expand_operand ops[6];
unsigned int nops;
