This patch fixes a bug with the calculation of array bounds in the
metadata for noncontiguous 'target update' directives. We record the
array base address, a bias and the array length to pass to libgomp --
but at present, we use the 'whole array size' for the last, which means
that at runtime we might look up an array with lower bound "base+bias"
and upper bound "base+bias+length", which for non-zero bias will overflow
the actual bounds of the array on the host and will (sometimes) return
an unrelated block instead of the correct one.
The fix is to instead calculate a size for the array that encloses the
elements to be transferred, and is guaranteed to be entirely within the
array (user errors excepted).
Tested with offloading to NVPTX. I will apply (to og13) shortly.
2023-07-11 Julian Brown <jul...@codesourcery.com>
gcc/
* omp-low.cc (lower_omp_target): Calculate volume enclosing
transferred elements instead of using whole array size for
noncontiguous 'target update' operations.
---
gcc/omp-low.cc | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc
index 05ac917fb27..c7706a5921f 100644
--- a/gcc/omp-low.cc
+++ b/gcc/omp-low.cc
@@ -14444,11 +14444,13 @@ lower_omp_target (gimple_stmt_iterator *gsi_p,
omp_context *ctx)
tree bias = size_zero_node;
tree volume = size_one_node;
+ tree enclosure = size_one_node;
for (i = dims - 1; i >= 0; i--)
{
tree dim = (*vdim)[i].value;
tree index = (*vindex)[i].value;
tree stride = (*vstride)[i].value;
+ tree len = (*vlen)[i].value;
/* For the bias we want, e.g.:
@@ -14463,6 +14465,20 @@ lower_omp_target (gimple_stmt_iterator *gsi_p,
omp_context *ctx)
size_binop (MULT_EXPR, volume,
index_stride));
volume = size_binop (MULT_EXPR, volume, dim);
+
+ if (i == 0)
+ {
+ tree elems_covered = size_binop (MINUS_EXPR, len,
+ size_one_node);
+ elems_covered = size_binop (MULT_EXPR, elems_covered,
+ stride);
+ elems_covered = size_binop (PLUS_EXPR, elems_covered,
+ size_one_node);
+ enclosure = size_binop (MULT_EXPR, enclosure,
+ elems_covered);
+ }
+ else
+ enclosure = volume;
}
/* If we don't have a separate span size, use the element size
@@ -14470,10 +14486,9 @@ lower_omp_target (gimple_stmt_iterator *gsi_p,
omp_context *ctx)
if (!span)
span = fold_convert (sizetype, elsize);
- /* The size of the whole array -- to make sure we find any
- part of the array via splay-tree lookup that might be
- mapped on the target at runtime. */
- OMP_CLAUSE_SIZE (oc) = size_binop (MULT_EXPR, arrsize, span);
+ /* The size of a volume enclosing the elements to be
+ transferred. */
+ OMP_CLAUSE_SIZE (oc) = size_binop (MULT_EXPR, enclosure, span);
/* And the bias of the first element we will update. */
OMP_CLAUSE_SIZE (dn) = size_binop (MULT_EXPR, bias, span);
--
2.41.0
