abs_step, &niter_access2))
return false;
+ bool waw_or_war_p = (alias_pair.flags & ~(DR_ALIAS_WAR | DR_ALIAS_WAW)) == 0;
+
unsigned int i;
for (i = 0; i < DR_NUM_DIMENSIONS (dr_a.dr); i++)
{
Combining the tests requires limit to be computable in an unsigned
form of the index type; if it isn't, we fall back to the usual
- pointer-based checks. */
- poly_offset_int limit = (idx_len1 + idx_access1 - 1
- + idx_len2 + idx_access2 - 1);
+ pointer-based checks.
+
+ We can do better if DR_B is a write and if DR_A and DR_B are
+ well-ordered in both the original and the new code (see the
+ comment above the DR_ALIAS_* flags for details). In this case
+ we know that for each i in [0, n-1], the write performed by
+ access i of DR_B occurs after access numbers j<=i of DR_A in
+ both the original and the new code. Any write or anti
+ dependencies wrt those DR_A accesses are therefore maintained.
+
+ We just need to make sure that each individual write in DR_B does not
+ overlap any higher-indexed access in DR_A; such DR_A accesses happen
+ after the DR_B access in the original code but happen before it in
+ the new code.
+
+ We know the steps for both accesses are equal, so by induction, we
+ just need to test whether the first write of DR_B overlaps a later
+ access of DR_A. In other words, we need to move min1 along by
+ one iteration:
+
+ min1' = min1 + idx_step
+
+ and use the ranges:
+
+ [min1' + low_offset1', min1' + high_offset1' + idx_access1 - 1]
+
+ and:
+
+ [min2, min2 + idx_access2 - 1]
+
+ where:
+
+ low_offset1' = +ve step ? 0 : -(idx_len1 - |idx_step|)
+ high_offset1' = +ve_step ? idx_len1 - |idx_step| : 0. */
+ if (waw_or_war_p)
+ idx_len1 -= abs_idx_step;
+
+ poly_offset_int limit = idx_len1 + idx_access1 - 1 + idx_access2 - 1;
+ if (!waw_or_war_p)
+ limit += idx_len2;
+
tree utype = unsigned_type_for (TREE_TYPE (min1));
if (!wi::fits_to_tree_p (limit, utype))
return false;
poly_offset_int low_offset1 = neg_step ? -idx_len1 : 0;
- poly_offset_int high_offset2 = neg_step ? 0 : idx_len2;
+ poly_offset_int high_offset2 = neg_step || waw_or_war_p ? 0 : idx_len2;
poly_offset_int bias = high_offset2 + idx_access2 - 1 - low_offset1;
+ /* Equivalent to adding IDX_STEP to MIN1. */
+ if (waw_or_war_p)
+ bias -= wi::to_offset (idx_step);
tree subject = fold_build2 (MINUS_EXPR, utype,
fold_convert (utype, min2),
*cond_expr = part_cond_expr;
}
if (dump_enabled_p ())
- dump_printf (MSG_NOTE, "using an index-based overlap test\n");
+ {
+ if (waw_or_war_p)
+ dump_printf (MSG_NOTE, "using an index-based WAR/WAW test\n");
+ else
+ dump_printf (MSG_NOTE, "using an index-based overlap test\n");
+ }
+ return true;
+}
+
+/* A subroutine of create_intersect_range_checks, with a subset of the
+ same arguments. Try to optimize cases in which the second access
+ is a write and in which some overlap is valid. */
+
+static bool
+create_waw_or_war_checks (tree *cond_expr,
+ const dr_with_seg_len_pair_t &alias_pair)
+{
+ const dr_with_seg_len& dr_a = alias_pair.first;
+ const dr_with_seg_len& dr_b = alias_pair.second;
+
+ /* Check for cases in which:
+
+ (a) DR_B is always a write;
+ (b) the accesses are well-ordered in both the original and new code
+ (see the comment above the DR_ALIAS_* flags for details); and
+ (c) the DR_STEPs describe all access pairs covered by ALIAS_PAIR. */
+ if (alias_pair.flags & ~(DR_ALIAS_WAR | DR_ALIAS_WAW))
+ return false;
+
+ /* Check for equal (but possibly variable) steps. */
+ tree step = DR_STEP (dr_a.dr);
+ if (!operand_equal_p (step, DR_STEP (dr_b.dr)))
+ return false;
+
+ /* Make sure that we can operate on sizetype without loss of precision. */
+ tree addr_type = TREE_TYPE (DR_BASE_ADDRESS (dr_a.dr));
+ if (TYPE_PRECISION (addr_type) != TYPE_PRECISION (sizetype))
+ return false;
+
+ /* All addresses involved are known to have a common alignment ALIGN.
+ We can therefore subtract ALIGN from an exclusive endpoint to get
+ an inclusive endpoint. In the best (and common) case, ALIGN is the
+ same as the access sizes of both DRs, and so subtracting ALIGN
+ cancels out the addition of an access size. */
+ unsigned int align = MIN (dr_a.align, dr_b.align);
+ poly_uint64 last_chunk_a = dr_a.access_size - align;
+ poly_uint64 last_chunk_b = dr_b.access_size - align;
+
+ /* Get a boolean expression that is true when the step is negative. */
+ tree indicator = dr_direction_indicator (dr_a.dr);
+ tree neg_step = fold_build2 (LT_EXPR, boolean_type_node,
+ fold_convert (ssizetype, indicator),
+ ssize_int (0));
+
+ /* Get lengths in sizetype. */
+ tree seg_len_a
+ = fold_convert (sizetype, rewrite_to_non_trapping_overflow (dr_a.seg_len));
+ step = fold_convert (sizetype, rewrite_to_non_trapping_overflow (step));
+
+ /* Each access has the following pattern:
+
+ <- |seg_len| ->
+ <--- A: -ve step --->
+ +-----+-------+-----+-------+-----+
+ | n-1 | ..... | 0 | ..... | n-1 |
+ +-----+-------+-----+-------+-----+
+ <--- B: +ve step --->
+ <- |seg_len| ->
+ |
+ base address
+
+ where "n" is the number of scalar iterations covered by the segment.
+
+ A is the range of bytes accessed when the step is negative,
+ B is the range when the step is positive.
+
+ We know that DR_B is a write. We also know (from checking that
+ DR_A and DR_B are well-ordered) that for each i in [0, n-1],
+ the write performed by access i of DR_B occurs after access numbers
+ j<=i of DR_A in both the original and the new code. Any write or
+ anti dependencies wrt those DR_A accesses are therefore maintained.
+
+ We just need to make sure that each individual write in DR_B does not
+ overlap any higher-indexed access in DR_A; such DR_A accesses happen
+ after the DR_B access in the original code but happen before it in
+ the new code.
+
+ We know the steps for both accesses are equal, so by induction, we
+ just need to test whether the first write of DR_B overlaps a later
+ access of DR_A. In other words, we need to move addr_a along by
+ one iteration:
+
+ addr_a' = addr_a + step
+
+ and check whether:
+
+ [addr_b, addr_b + last_chunk_b]
+
+ overlaps:
+
+ [addr_a' + low_offset_a, addr_a' + high_offset_a + last_chunk_a]
+
+ where [low_offset_a, high_offset_a] spans accesses [1, n-1]. I.e.:
+
+ low_offset_a = +ve step ? 0 : seg_len_a - step
+ high_offset_a = +ve step ? seg_len_a - step : 0
+
+ This is equivalent to testing whether:
+
+ addr_a' + low_offset_a <= addr_b + last_chunk_b
+ && addr_b <= addr_a' + high_offset_a + last_chunk_a
+
+ Converting this into a single test, there is an overlap if:
+
+ 0 <= addr_b + last_chunk_b - addr_a' - low_offset_a <= limit
+
+ where limit = high_offset_a - low_offset_a + last_chunk_a + last_chunk_b
+
+ If DR_A is performed, limit + |step| - last_chunk_b is known to be
+ less than the size of the object underlying DR_A. We also know
+ that last_chunk_b <= |step|; this is checked elsewhere if it isn't
+ guaranteed at compile time. There can therefore be no overflow if
+ "limit" is calculated in an unsigned type with pointer precision. */
+ tree addr_a = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_a.dr),
+ DR_OFFSET (dr_a.dr));
+ addr_a = fold_build_pointer_plus (addr_a, DR_INIT (dr_a.dr));
+
+ tree addr_b = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_b.dr),
+ DR_OFFSET (dr_b.dr));
+ addr_b = fold_build_pointer_plus (addr_b, DR_INIT (dr_b.dr));
+
+ /* Advance ADDR_A by one iteration and adjust the length to compensate. */
+ addr_a = fold_build_pointer_plus (addr_a, step);
+ tree seg_len_a_minus_step = fold_build2 (MINUS_EXPR, sizetype,
+ seg_len_a, step);
+ if (!CONSTANT_CLASS_P (seg_len_a_minus_step))
+ seg_len_a_minus_step = build1 (SAVE_EXPR, sizetype, seg_len_a_minus_step);
+
+ tree low_offset_a = fold_build3 (COND_EXPR, sizetype, neg_step,
+ seg_len_a_minus_step, size_zero_node);
+ if (!CONSTANT_CLASS_P (low_offset_a))
+ low_offset_a = build1 (SAVE_EXPR, sizetype, low_offset_a);
+
+ /* We could use COND_EXPR <neg_step, size_zero_node, seg_len_a_minus_step>,
+ but it's usually more efficient to reuse the LOW_OFFSET_A result. */
+ tree high_offset_a = fold_build2 (MINUS_EXPR, sizetype, seg_len_a_minus_step,
+ low_offset_a);
+
+ /* The amount added to addr_b - addr_a'. */
+ tree bias = fold_build2 (MINUS_EXPR, sizetype,
+ size_int (last_chunk_b), low_offset_a);
+
+ tree limit = fold_build2 (MINUS_EXPR, sizetype, high_offset_a, low_offset_a);
+ limit = fold_build2 (PLUS_EXPR, sizetype, limit,
+ size_int (last_chunk_a + last_chunk_b));
+
+ tree subject = fold_build2 (POINTER_DIFF_EXPR, ssizetype, addr_b, addr_a);
+ subject = fold_build2 (PLUS_EXPR, sizetype,
+ fold_convert (sizetype, subject), bias);
+
+ *cond_expr = fold_build2 (GT_EXPR, boolean_type_node, subject, limit);
+ if (dump_enabled_p ())
+ dump_printf (MSG_NOTE, "using an address-based WAR/WAW test\n");
return true;
}
if (create_intersect_range_checks_index (loop, cond_expr, alias_pair))
return;
+ if (create_waw_or_war_checks (cond_expr, alias_pair))
+ return;
+
unsigned HOST_WIDE_INT min_align;
tree_code cmp_code;
/* We don't have to check DR_ALIAS_MIXED_STEPS here, since both versions
projects / gcc.git / commitdiff