re PR tree-optimization/86062 (Missed redundancy elimination with struct and array)

2018-06-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/86062
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle arbitrary
	component refs ontop
	of to be offsetted base.

	* g++.dg/tree-ssa/pr86062.C: New testcase.

From-SVN: r261231

gcc/ChangeLog

+2018-06-06  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/86062
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle arbitrary
+	component refs ontop
+	of to be offsetted base.
+
 2018-06-06  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
 
 	* gcc/config/msp430/msp430.c (msp430_attr): Allow interrupt handlers

gcc/testsuite/ChangeLog

+2018-06-06  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/86062
+	* g++.dg/tree-ssa/pr86062.C: New testcase.
+
 2018-06-05  Steve Ellcey  <sellcey@cavium.com>
 
 	PR target/79924

gcc/testsuite/g++.dg/tree-ssa/pr86062.C

+// { dg-do compile }
+// { dg-require-effective-target c++14 }
+// { dg-options "-O2 -ffinite-math-only -fdump-tree-fre1" }
+
+#include <array>
+
+struct I { double i,s; I(double d):i(d),s(d){} };
+typedef std::array<double,3> P;
+typedef std::array<I,3> AP;
+
+static AP c(P const&p){
+      return {p[0],p[1],p[2]};
+}
+template<class T> auto const& ac(T const&p, int n){return p[n];}
+static double g(P const&p, int n)
+{
+    I res = ac(c(p),n);
+      return res.s-res.i;
+}
+
+__attribute__((flatten)) double fff(P p){ return g(p,1); }
+
+// { dg-final { scan-tree-dump "return 0.0;" "fre1" } }

gcc/tree-ssa-sccvn.c

@@ -2270,14 +2270,16 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_,
       /* Apply an extra offset to the inner MEM_REF of the RHS.  */
       if (maybe_ne (extra_off, 0))
 	{
-	  if (rhs.length () < 2
-	      || rhs[0].opcode != MEM_REF
-	      || known_eq (rhs[0].off, -1))
+	  if (rhs.length () < 2)
 	    return (void *)-1;
-	  rhs[0].off += extra_off;
-	  rhs[0].op0 = int_const_binop (PLUS_EXPR, rhs[0].op0,
-					build_int_cst (TREE_TYPE (rhs[0].op0),
-						       extra_off));
+	  int ix = rhs.length () - 2;
+	  if (rhs[ix].opcode != MEM_REF
+	      || known_eq (rhs[ix].off, -1))
+	    return (void *)-1;
+	  rhs[ix].off += extra_off;
+	  rhs[ix].op0 = int_const_binop (PLUS_EXPR, rhs[ix].op0,
+					 build_int_cst (TREE_TYPE (rhs[ix].op0),
+							extra_off));
 	}
 
       /* We need to pre-pend vr->operands[0..i] to rhs.  */