[PATCH] Fix PR60505

Cong Hou congh@google.com
Wed Mar 19 19:23:00 GMT 2014


On Tue, Mar 18, 2014 at 4:43 AM, Richard Biener <rguenther@suse.de> wrote:
>
> On Mon, 17 Mar 2014, Cong Hou wrote:
>
> > On Mon, Mar 17, 2014 at 6:44 AM, Richard Biener <rguenther@suse.de> wrote:
> > > On Fri, 14 Mar 2014, Cong Hou wrote:
> > >
> > >> On Fri, Mar 14, 2014 at 12:58 AM, Richard Biener <rguenther@suse.de> wrote:
> > >> > On Fri, 14 Mar 2014, Jakub Jelinek wrote:
> > >> >
> > >> >> On Fri, Mar 14, 2014 at 08:52:07AM +0100, Richard Biener wrote:
> > >> >> > > Consider this fact and if there are alias checks, we can safely remove
> > >> >> > > the epilogue if the maximum trip count of the loop is less than or
> > >> >> > > equal to the calculated threshold.
> > >> >> >
> > >> >> > You have to consider n % vf != 0, so an argument on only maximum
> > >> >> > trip count or threshold cannot work.
> > >> >>
> > >> >> Well, if you only check if maximum trip count is <= vf and you know
> > >> >> that for n < vf the vectorized loop + it's epilogue path will not be taken,
> > >> >> then perhaps you could, but it is a very special case.
> > >> >> Now, the question is when we are guaranteed we enter the scalar versioned
> > >> >> loop instead for n < vf, is that in case of versioning for alias or
> > >> >> versioning for alignment?
> > >> >
> > >> > I think neither - I have plans to do the cost model check together
> > >> > with the versioning condition but didn't get around to implement that.
> > >> > That would allow stronger max bounds for the epilogue loop.
> > >>
> > >> In vect_transform_loop(), check_profitability will be set to true if
> > >> th >= VF-1 and the number of iteration is unknown (we only consider
> > >> unknown trip count here), where th is calculated based on the
> > >> parameter PARAM_MIN_VECT_LOOP_BOUND and cost model, with the minimum
> > >> value VF-1. If the loop needs to be versioned, then
> > >> check_profitability with true value will be passed to
> > >> vect_loop_versioning(), in which an enhanced loop bound check
> > >> (considering cost) will be built. So I think if the loop is versioned
> > >> and n < VF, then we must enter the scalar version, and in this case
> > >> removing epilogue should be safe when the maximum trip count <= th+1.
> > >
> > > You mean exactly in the case where the profitability check ensures
> > > that n % vf == 0?  Thus effectively if n == maximum trip count?
> > > That's quite a special case, no?
> >
> >
> > Yes, it is a special case. But it is in this special case that those
> > warnings are thrown out. Also, I think declaring an array with VF*N as
> > length is not unusual.
>
> Ok, but then for the patch compute the cost model threshold once
> in vect_analyze_loop_2 and store it in a new
> LOOP_VINFO_COST_MODEL_THRESHOLD.


Done.


> Also you have to check
> the return value from max_stmt_executions_int as that may return
> -1 if the number cannot be computed (or isn't representable in
> a HOST_WIDE_INT).


It will be converted to unsigned type so that -1 means infinity.


> You also should check for
> LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT which should have the
> same effect on the cost model check.


Done.


>
>
> The existing condition is already complicated enough - adding new
> stuff warrants comments before the (sub-)checks.


OK. Comments added.

Below is the revised patch. Bootstrapped and tested on a x86-64 machine.


Cong



diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e1d8666..eceefb3 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,18 @@
+2014-03-11  Cong Hou  <congh@google.com>
+
+ PR tree-optimization/60505
+ * tree-vectorizer.h (struct _stmt_vec_info): Add th field as the
+ threshold of number of iterations below which no vectorization will be
+ done.
+ * tree-vect-loop.c (new_loop_vec_info):
+ Initialize LOOP_VINFO_COST_MODEL_THRESHOLD.
+ * tree-vect-loop.c (vect_analyze_loop_operations):
+ Set LOOP_VINFO_COST_MODEL_THRESHOLD.
+ * tree-vect-loop.c (vect_transform_loop):
+ Use LOOP_VINFO_COST_MODEL_THRESHOLD.
+ * tree-vect-loop.c (vect_analyze_loop_2): Check the maximum number
+ of iterations of the loop and see if we should build the epilogue.
+
 2014-03-10  Jakub Jelinek  <jakub@redhat.com>

  PR ipa/60457
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 41b6875..09ec1c0 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-03-11  Cong Hou  <congh@google.com>
+
+ PR tree-optimization/60505
+ * gcc.dg/vect/pr60505.c: New test.
+
 2014-03-10  Jakub Jelinek  <jakub@redhat.com>

  PR ipa/60457
diff --git a/gcc/testsuite/gcc.dg/vect/pr60505.c
b/gcc/testsuite/gcc.dg/vect/pr60505.c
new file mode 100644
index 0000000..6940513
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr60505.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Wall -Werror" } */
+
+void foo(char *in, char *out, int num)
+{
+  int i;
+  char ovec[16] = {0};
+
+  for(i = 0; i < num ; ++i)
+    out[i] = (ovec[i] = in[i]);
+  out[num] = ovec[num/2];
+}
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index df6ab6f..1c78e11 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -933,6 +933,7 @@ new_loop_vec_info (struct loop *loop)
   LOOP_VINFO_NITERS (res) = NULL;
   LOOP_VINFO_NITERS_UNCHANGED (res) = NULL;
   LOOP_VINFO_COST_MODEL_MIN_ITERS (res) = 0;
+  LOOP_VINFO_COST_MODEL_THRESHOLD (res) = 0;
   LOOP_VINFO_VECTORIZABLE_P (res) = 0;
   LOOP_VINFO_PEELING_FOR_ALIGNMENT (res) = 0;
   LOOP_VINFO_VECT_FACTOR (res) = 0;
@@ -1579,6 +1580,8 @@ vect_analyze_loop_operations (loop_vec_info
loop_vinfo, bool slp)
           || min_profitable_iters > min_scalar_loop_bound))
     th = (unsigned) min_profitable_iters;

+  LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo) = th;
+
   if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
       && LOOP_VINFO_INT_NITERS (loop_vinfo) <= th)
     {
@@ -1625,6 +1628,7 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)
   bool ok, slp = false;
   int max_vf = MAX_VECTORIZATION_FACTOR;
   int min_vf = 2;
+  unsigned int th;

   /* Find all data references in the loop (which correspond to vdefs/vuses)
      and analyze their evolution in the loop.  Also adjust the minimal
@@ -1769,6 +1773,10 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)

   /* Decide whether we need to create an epilogue loop to handle
      remaining scalar iterations.  */
+  th = ((LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo) + 1)
+        / LOOP_VINFO_VECT_FACTOR (loop_vinfo))
+       * LOOP_VINFO_VECT_FACTOR (loop_vinfo);
+
   if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
       && LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo) > 0)
     {
@@ -1779,7 +1787,14 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)
     }
   else if (LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo)
    || (tree_ctz (LOOP_VINFO_NITERS (loop_vinfo))
-       < (unsigned)exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))))
+       < (unsigned)exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))
+               /* In case of versioning, check if the maximum number of
+                  iterations is greater than th.  If they are identical,
+                  the epilogue is unnecessary.  */
+       && ((!LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo)
+            && !LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT (loop_vinfo))
+                   || (unsigned HOST_WIDE_INT)max_stmt_executions_int
+        (LOOP_VINFO_LOOP (loop_vinfo)) > th)))
     LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo) = true;

   /* If an epilogue loop is required make sure we can create one.  */
@@ -5775,9 +5790,7 @@ vect_transform_loop (loop_vec_info loop_vinfo)
      by our caller.  If the threshold makes all loops profitable that
      run at least the vectorization factor number of times checking
      is pointless, too.  */
-  th = ((PARAM_VALUE (PARAM_MIN_VECT_LOOP_BOUND)
- * LOOP_VINFO_VECT_FACTOR (loop_vinfo)) - 1);
-  th = MAX (th, LOOP_VINFO_COST_MODEL_MIN_ITERS (loop_vinfo));
+  th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
   if (th >= LOOP_VINFO_VECT_FACTOR (loop_vinfo) - 1
       && !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo))
     {
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index f8efe47..f2087e2 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -264,6 +264,11 @@ typedef struct _loop_vec_info {
      values unknown at compile time.  */
   int min_profitable_iters;

+  /* Threshold of number of iterations below which vectorzation will not be
+     performed. It is calculated from MIN_PROFITABLE_ITERS and
+     PARAM_MIN_VECT_LOOP_BOUND.  */
+  unsigned int th;
+
   /* Is the loop vectorizable? */
   bool vectorizable;

@@ -382,6 +387,7 @@ typedef struct _loop_vec_info {
    cost model.  */
 #define LOOP_VINFO_NITERS_UNCHANGED(L)     (L)->num_iters_unchanged
 #define LOOP_VINFO_COST_MODEL_MIN_ITERS(L) (L)->min_profitable_iters
+#define LOOP_VINFO_COST_MODEL_THRESHOLD(L) (L)->th
 #define LOOP_VINFO_VECTORIZABLE_P(L)       (L)->vectorizable
 #define LOOP_VINFO_VECT_FACTOR(L)          (L)->vectorization_factor
 #define LOOP_VINFO_PTR_MASK(L)             (L)->ptr_mask





>
>
> Richard.



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