Currently a load from a constant table gets the range of the whole
table, no matter what is known of its index. For example, with
static const int tbl[4] = { 0, 5, 6, 7 };
and i in [0, 1], tbl[i] is currently [0, 0][5, 7]. With this patch we
get [0, 0][5, 5].
This work comes from my DOM parity obsession, but goes beyond what DOM
gets here. DOM folds a load from a constant table only when the index
can be determined to be a constant, as on the path through i = 1 in:
if (c)
i = 1;
if (tbl[i] == 5)
With this patch we also narrow a load whose index is in a range:
if (i < 2 && tbl[i] > 5)
tbl[i] is [0, 0][5, 5], and we can fold the comparison away.
This implements the following TODO in the code:
/* TODO: If the array index in the expr is an SSA_NAME with a known
range, we could use just values loaded from the corresponding array
elements. */
Oh, and we no longer have to special case INTEGER_CSTs, as ranger
happily handles those.
I've also added a testcase for r17-4029-g7dab38c9d7104e, a phiopt
tweak which couldn't be properly tested until now.
Tested on ppc64le Linux.
gcc/ChangeLog:
* gimple-range-fold.cc (intersects_p): New.
(class ctor_ref_range): Add SRC.
(ctor_ref_range::accumulate_range_from_array_ref): Load only from
the elements the range of the index reaches, a constant index
included.
(fold_using_range::fold_stmt): Pass the source to
range_from_readonly_var.
(fold_using_range::range_from_readonly_var): Add SRC.
* gimple-range-fold.h (fold_using_range::range_from_readonly_var):
Adjust.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/phi-opt-52.c: New test.
* gcc.dg/tree-ssa/vrp-from-cst-agg-10.c: New test.
* gcc.dg/tree-ssa/vrp-from-cst-agg-11.c: New test.
* gcc.dg/tree-ssa/vrp-from-cst-agg-13.c: New test.
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