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re PR middle-end/71310 (Bitfields cause load hit store with smaller store and larger load) 

2016-06-14  Richard Biener  <rguenther@suse.de>

	PR middle-end/71310
	PR bootstrap/71510
	* expr.h (get_bit_range): Declare.
	* expr.c (get_bit_range): Export.
	* fold-const.c (optimize_bit_field_compare): Use get_bit_range and
	word_mode again to constrain the bitfield access.

From-SVN: r237426
This commit is contained in:
Richard Biener 2016-06-14 07:26:52 +00:00 committed by Richard Biener
parent 90b72e84c4
commit 585334d41d
4 changed files with 22 additions and 10 deletions
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9
gcc/ChangeLog
View File

@ -1,3 +1,12 @@
2016-06-14 Richard Biener <rguenther@suse.de>
PR middle-end/71310
PR bootstrap/71510
* expr.h (get_bit_range): Declare.
* expr.c (get_bit_range): Export.
* fold-const.c (optimize_bit_field_compare): Use get_bit_range and
word_mode again to constrain the bitfield access.
2016-06-14 Richard Biener <rguenther@suse.de>
PR tree-optimization/71521

2
gcc/expr.c
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@ -4795,7 +4795,7 @@ optimize_bitfield_assignment_op (unsigned HOST_WIDE_INT bitsize,
If the access does not need to be restricted, 0 is returned in both
*BITSTART and *BITEND. */
static void
void
get_bit_range (unsigned HOST_WIDE_INT *bitstart,
unsigned HOST_WIDE_INT *bitend,
tree exp,

4
gcc/expr.h
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@ -242,6 +242,10 @@ extern rtx push_block (rtx, int, int);
extern bool emit_push_insn (rtx, machine_mode, tree, rtx, unsigned int,
int, rtx, int, rtx, rtx, int, rtx, bool);
/* Extract the accessible bit-range from a COMPONENT_REF. */
extern void get_bit_range (unsigned HOST_WIDE_INT *, unsigned HOST_WIDE_INT *,
tree, HOST_WIDE_INT *, tree *);
/* Expand an assignment that stores the value of FROM into TO. */
extern void expand_assignment (tree, tree, bool);

17
gcc/fold-const.c
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@ -3902,24 +3902,23 @@ optimize_bit_field_compare (location_t loc, enum tree_code code,
return 0;
}
/* Don't use a larger mode for reading the bit field than we will
use in other places accessing the bit field. */
machine_mode largest_mode = word_mode;
/* Honor the C++ memory model and mimic what RTL expansion does. */
unsigned HOST_WIDE_INT bitstart = 0;
unsigned HOST_WIDE_INT bitend = 0;
if (TREE_CODE (lhs) == COMPONENT_REF)
{
tree field = TREE_OPERAND (lhs, 1);
tree repr = DECL_BIT_FIELD_REPRESENTATIVE (field);
if (repr)
largest_mode = DECL_MODE (repr);
get_bit_range (&bitstart, &bitend, lhs, &lbitpos, &offset);
if (offset != NULL_TREE)
return 0;
}
/* See if we can find a mode to refer to this field. We should be able to,
but fail if we can't. */
nmode = get_best_mode (lbitsize, lbitpos, 0, 0,
nmode = get_best_mode (lbitsize, lbitpos, bitstart, bitend,
const_p ? TYPE_ALIGN (TREE_TYPE (linner))
: MIN (TYPE_ALIGN (TREE_TYPE (linner)),
TYPE_ALIGN (TREE_TYPE (rinner))),
largest_mode, false);
word_mode, false);
if (nmode == VOIDmode)
return 0;