[PATCH] Fix PR87931

Richard Biener rguenther@suse.de
Tue Nov 13 12:59:00 GMT 2018


We need to restrict what we handle as last operation in a nested
cycle because vectorizable_reduction performs the code-generation
in the end.

Boostrap and regtest in progress on x86_64-unknown-linux-gnu.

Richard.

2018-11-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87931
	* tree-vect-loop.c (vect_is_simple_reduction): Restrict
	nested cycles we support to latch computations vectorizable_reduction
	handles.

	* gcc.dg/graphite/pr87931.c: New testcase.

Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c	(revision 266061)
+++ gcc/tree-vect-loop.c	(working copy)
@@ -2983,6 +2976,22 @@ vect_is_simple_reduction (loop_vec_info
 
   if (nested_in_vect_loop && !check_reduction)
     {
+      /* FIXME: Even for non-reductions code generation is funneled
+	 through vectorizable_reduction for the stmt defining the
+	 PHI latch value.  So we have to artificially restrict ourselves
+	 for the supported operations.  */
+      switch (get_gimple_rhs_class (code))
+	{
+	case GIMPLE_BINARY_RHS:
+	case GIMPLE_TERNARY_RHS:
+	  break;
+	default:
+	  /* Not supported by vectorizable_reduction.  */
+	  if (dump_enabled_p ())
+	    report_vect_op (MSG_MISSED_OPTIMIZATION, def_stmt,
+			    "nested cycle: not handled operation: ");
+	  return NULL;
+	}
       if (dump_enabled_p ())
 	report_vect_op (MSG_NOTE, def_stmt, "detected nested cycle: ");
       return def_stmt_info;
Index: gcc/testsuite/gcc.dg/graphite/pr87931.c
===================================================================
--- gcc/testsuite/gcc.dg/graphite/pr87931.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/graphite/pr87931.c	(working copy)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fno-tree-copy-prop -fgraphite-identity" } */
+
+#define N 40
+#define M 128
+float in[N+M];
+float coeff[M];
+float fir_out[N];
+
+void fir ()
+{
+  int i,j,k;
+  float diff;
+
+  for (i = 0; i < N; i++) {
+    diff = 0;
+    for (j = 0; j < M; j++) {
+      diff += in[j+i]*coeff[j];
+    }
+    fir_out[i] = diff;
+  }
+}



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