At present we reject uncounted loops outright when doing initial loop
analysis in `vect_analyze_loop_form'.
We have the following gating condition that causes rejection of a
given loop:
if (integer_zerop (info->assumptions)
|| !info->number_of_iterations
|| chrec_contains_undetermined (info->number_of_iterations))
We can do away with this check altogether, but not without problems,
allowing many malformed loops through which ought to be rejected as
early as possible.
We observe that a common thread running through these malformed loops
is the absence of any scalar evolution between iterations.
We have therefore adjusted the analysis replacing the checks on
`niters' for a test for the presence of scalar evolution in the loop,
which can be detected via the presence of phi nodes in the loop.
- Detecting uncounted loops going forward:
Given that scalar evolution analysis of uncounted loops sets
`loop_vec_info->num_iters' to `SCEV_NOT_KNOWN', we use this as the
criterion for probing whether a loop is uncounted or not.
Consequently, we introduce a new access function on `loop_vec_info' to
conveniently test whether a loop in question is uncounted or not, in
the form of `LOOP_VINFO_NITERS_UNCOUNTED_P(L)'.
gcc/ChangeLog:
* tree-vect-loop.cc (vect_analyze_loop_form): Relax niters
condition.
* tree-vectorizer.h (LOOP_VINFO_NITERS_UNCOUNTED_P): New.
---
gcc/tree-vect-loop.cc | 31 ++++++++++++++++++++++++++++---
gcc/tree-vectorizer.h | 2 ++
2 files changed, 30 insertions(+), 3 deletions(-)
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index b11b4c168ab..d428f3a11a4 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -1469,6 +1469,20 @@ vect_analyze_loop_form (class loop *loop, gimple
*loop_vectorized_call,
"not vectorized:"
" unsupported control flow in loop.\n");
}
+
+ /* Check if we have any control flow that doesn't leave the loop. */
+ bool has_phi = false;
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ if (!gimple_seq_empty_p (phi_nodes (bbs[i])))
+ {
+ has_phi = true;
+ break;
+ }
+ if (!has_phi)
+ return opt_result::failure_at (vect_location,
+ "not vectorized:"
+ " no scalar evolution detected in loop.\n");
+
free (bbs);
/* Different restrictions apply when we are considering an inner-most loop,
@@ -1593,9 +1607,20 @@ vect_analyze_loop_form (class loop *loop, gimple
*loop_vectorized_call,
std::swap (info->conds[0], info->conds[i]);
}
- if (integer_zerop (info->assumptions)
- || !info->number_of_iterations
- || chrec_contains_undetermined (info->number_of_iterations))
+ if (chrec_contains_undetermined (info->number_of_iterations))
+ {
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "Loop being analyzed as uncounted.\n");
+ if (loop->inner)
+ return opt_result::failure_at
+ (vect_location,
+ "not vectorized: outer loop vectorization of uncounted loops"
+ " is unsupported.\n");
+ return opt_result::success ();
+ }
+
+ if (integer_zerop (info->assumptions))
return opt_result::failure_at
(info->conds[0],
"not vectorized: number of iterations cannot be computed.\n");
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 55f0bee0eb7..a16bb7c477d 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -1258,6 +1258,8 @@ public:
/* Since LOOP_VINFO_NITERS and LOOP_VINFO_NITERSM1 can change after
prologue peeling retain total unchanged scalar loop iterations for
cost model. */
+#define LOOP_VINFO_NITERS_UNCOUNTED_P(L) (LOOP_VINFO_NITERS (L) \
+ == chrec_dont_know)
#define LOOP_VINFO_NITERS_UNCHANGED(L) (L)->num_iters_unchanged
#define LOOP_VINFO_NITERS_ASSUMPTIONS(L) (L)->num_iters_assumptions
#define LOOP_VINFO_COST_MODEL_THRESHOLD(L) (L)->th
--
2.43.0
