re PR tree-optimization/79578 (Unnecessary instructions in generated code)

	PR tree-optimization/79578
	* tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
	to compare base operands.

	PR tree-optimization/79578
	* g++.dg/tree-ssa/ssa-dse-3.C: New test.

From-SVN: r245675

gcc/ChangeLog

+2017-02-22 Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/79578
+	* tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
+	to compare base operands.
+
 2017-02-22  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	PR target/79211

gcc/testsuite/ChangeLog

+2017-02-22  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/79578
+	* g++.dg/tree-ssa/ssa-dse-3.C: New test.
+
 2017-02-22  Sameera Deshpande  <sameera.deshpande@imgtec.com>
 
 	* gcc.target/mips/msa-fp-cc.c: New test.

gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C

+/* { dg-do compile } */
+/* { dg-options "-std=c++14 -O3 -fdump-tree-dse1-details" } */
+
+#include <new>
+#include <cstdint>
+
+struct A
+{
+    std::uint16_t a, b;
+};
+
+A* f(char* b) __attribute__((noinline));
+
+A* f(char* b) {
+    auto a = new(b) A{};
+    a->a = 1;
+    a->b = 2;
+    return a;
+}
+
+int main() {
+    char b[sizeof(A)] alignas(A);
+    f(b);
+}
+
+
+/* { dg-final { scan-tree-dump "Deleted dead store: " "dse1" } } */
+

gcc/tree-ssa-dse.c

@@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple *stmt, ao_ref *ref)
   /* Verify we have the same base memory address, the write
      has a known size and overlaps with REF.  */
   if (valid_ao_ref_for_dse (&write)
-      && write.base == ref->base
+      && operand_equal_p (write.base, ref->base, 0)
       && write.size == write.max_size
       && ((write.offset < ref->offset
 	   && write.offset + write.size > ref->offset)