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[PATCH] Improve vectorizer dependence analysis
- From: Richard Biener <rguenther at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Date: Tue, 14 Jun 2016 16:03:55 +0200 (CEST)
- Subject: [PATCH] Improve vectorizer dependence analysis
- Authentication-results: sourceware.org; auth=none
The following patch makes us handle strided group stores in the
vectorizer dependence analysis code as our general dependence
code cannot handle {0, +, s_1} vs. {1, +, s_1} resulting from
a[i] = ..;
a[i+1] = ..;
i+=s;
this prevents the strided store support enhancement from triggering
on symbolic strided stores (it still triggers for constant-step
aka groups with gaps stores).
I also took the opportunity to remove read-read and self dependence
computations - those were never necessary for loop vectorization.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
Richard.
2016-06-14 Richard Biener <rguenther@suse.de>
* tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Do
not consider dependences between accesses that belong to the
same group.
(vect_analyze_data_ref_dependences): Do not analyze read-read
or self-dependences.
Index: gcc/tree-vect-data-refs.c
===================================================================
*** gcc/tree-vect-data-refs.c (revision 237428)
--- gcc/tree-vect-data-refs.c (working copy)
*************** vect_analyze_data_ref_dependence (struct
*** 227,232 ****
--- 231,242 ----
|| (DR_IS_READ (dra) && DR_IS_READ (drb)))
return false;
+ /* We do not have to consider dependences between accesses that belong
+ to the same group. */
+ if (GROUP_FIRST_ELEMENT (stmtinfo_a)
+ && GROUP_FIRST_ELEMENT (stmtinfo_a) == GROUP_FIRST_ELEMENT (stmtinfo_b))
+ return false;
+
/* Even if we have an anti-dependence then, as the vectorized loop covers at
least two scalar iterations, there is always also a true dependence.
As the vectorizer does not re-order loads and stores we can ignore
*************** vect_analyze_data_ref_dependences (loop_
*** 469,475 ****
LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = true;
if (!compute_all_dependences (LOOP_VINFO_DATAREFS (loop_vinfo),
&LOOP_VINFO_DDRS (loop_vinfo),
! LOOP_VINFO_LOOP_NEST (loop_vinfo), true))
return false;
FOR_EACH_VEC_ELT (LOOP_VINFO_DDRS (loop_vinfo), i, ddr)
--- 501,507 ----
LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = true;
if (!compute_all_dependences (LOOP_VINFO_DATAREFS (loop_vinfo),
&LOOP_VINFO_DDRS (loop_vinfo),
! LOOP_VINFO_LOOP_NEST (loop_vinfo), false))
return false;
FOR_EACH_VEC_ELT (LOOP_VINFO_DDRS (loop_vinfo), i, ddr)