[PATCH] PR 71483 - Fix live SLP operations

[Richard Biener]

On June 14, 2016 4:14:20 PM GMT+02:00, Alan Hayward <alan.hayward@arm.com> wrote:
>In the given testcase, g++ splits a live operation into two scalar
>statements
>and four vector statements.
>
>_5 = _4 >> 2;
>  _7 = (short int) _5;
>
>Is turned into:
>
>vect__5.32_80 = vect__4.31_76 >> 2;
>  vect__5.32_81 = vect__4.31_77 >> 2;
>  vect__5.32_82 = vect__4.31_78 >> 2;
>  vect__5.32_83 = vect__4.31_79 >> 2;
>  vect__7.33_86 = VEC_PACK_TRUNC_EXPR <vect__5.32_80, vect__5.32_81>;
>  vect__7.33_87 = VEC_PACK_TRUNC_EXPR <vect__5.32_82, vect__5.32_83>;
>
>_5 is then accessed outside the loop.
>
>This patch ensures that vectorizable_live_operation picks the correct
>scalar
>statement.
>I removed the "three possibilites" comment because it was no longer
>accurate
>(it's also possible to have more vector statements than scalar
>statements)
>and
>the calculation is now much simpler.
>
>Tested on x86 and aarch64.
>Ok to commit?

OK.

Thanks,
Richard.

>gcc/
>    PR tree-optimization/71483
>   * tree-vect-loop.c (vectorizable_live_operation): Pick correct index
>    for slp
>
>testsuite/g++.dg/vect
>    PR tree-optimization/71483
>    * pr71483.c: New
>
>
>Alan.
>
>
>diff --git a/gcc/testsuite/g++.dg/vect/pr71483.c
>b/gcc/testsuite/g++.dg/vect/pr71483.c
>new file mode 100644
>index 
>0000000000000000000000000000000000000000..77f879c9a89b8b41ef9dde3c343591857
>2dc8d01
>--- /dev/null
>+++ b/gcc/testsuite/g++.dg/vect/pr71483.c
>@@ -0,0 +1,11 @@
>+/* { dg-do compile } */
>+int b, c, d;
>+short *e;
>+void fn1() {
>+  for (; b; b--) {
>+    d = *e >> 2;
>+    *e++ = d;
>+    c = *e;
>+    *e++ = d;
>+  }
>+}
>diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
>index 
>4c8678505df6ec572b69fd7d12ac55cf4619ece6..a2413bf9c678d11cc2ffd22bc7d984e91
>1831804 100644
>--- a/gcc/tree-vect-loop.c
>+++ b/gcc/tree-vect-loop.c
>@@ -6368,24 +6368,20 @@ vectorizable_live_operation (gimple *stmt,
>
>       int num_scalar = SLP_TREE_SCALAR_STMTS (slp_node).length ();
>       int num_vec = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
>-      int scalar_per_vec = num_scalar / num_vec;
>
>-      /* There are three possibilites here:
>-	 1: All scalar stmts fit in a single vector.
>-	 2: All scalar stmts fit multiple times into a single vector.
>-	    We must choose the last occurence of stmt in the vector.
>-	 3: Scalar stmts are split across multiple vectors.
>-	    We must choose the correct vector and mod the lane accordingly. 
>*/
>+      /* Get the last occurrence of the scalar index from the
>concatenation of
>+	 all the slp vectors. Calculate which slp vector it is and the index
>+	 within.  */
>+      int pos = (num_vec * nunits) - num_scalar + slp_index;
>+      int vec_entry = pos / nunits;
>+      int vec_index = pos % nunits;
>
>       /* Get the correct slp vectorized stmt.  */
>-      int vec_entry = slp_index / scalar_per_vec;
>   vec_lhs = gimple_get_lhs (SLP_TREE_VEC_STMTS (slp_node)[vec_entry]);
>
>       /* Get entry to use.  */
>-      bitstart = build_int_cst (unsigned_type_node,
>-				scalar_per_vec - (slp_index % scalar_per_vec));
>+      bitstart = build_int_cst (unsigned_type_node, vec_index);
>       bitstart = int_const_binop (MULT_EXPR, bitsize, bitstart);
>-      bitstart = int_const_binop (MINUS_EXPR, vec_bitsize, bitstart);
>     }
>   else
>     {