[PATCH] rs6000: Enable overlapped by-pieces operations

[HAO CHEN GUI]

Hi,
  This patch enables overlapped by-piece operations. On rs6000, default
move/set/clear ratio is 2. So the overlap is only enabled with compare
by-pieces.

  Bootstrapped and tested on powerpc64-linux BE and LE with no
regressions. Is it OK for the trunk?

Thanks
Gui Haochen

ChangeLog
rs6000: Enable overlapped by-pieces operations

This patch enables overlapped by-piece operations by defining
TARGET_OVERLAP_OP_BY_PIECES_P to true.  On rs6000, default move/set/clear
ratio is 2.  So the overlap is only enabled with compare by-pieces.

gcc/
        * config/rs6000/rs6000.cc (TARGET_OVERLAP_OP_BY_PIECES_P): Define.

gcc/testsuite/
        * gcc.target/powerpc/block-cmp-9.c: New.


patch.diff
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 6b9a40fcc66..2b5f5cf1d86 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -1774,6 +1774,9 @@ static const scoped_attribute_specs *const 
rs6000_attribute_table[] =
 #undef TARGET_CONST_ANCHOR
 #define TARGET_CONST_ANCHOR 0x8000

+#undef TARGET_OVERLAP_OP_BY_PIECES_P
+#define TARGET_OVERLAP_OP_BY_PIECES_P hook_bool_void_true
+
 

 /* Processor table.  */
diff --git a/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c 
b/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c
new file mode 100644
index 00000000000..b5f51affbb7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mdejagnu-cpu=power8" } */
+/* { dg-final { scan-assembler-not {\ml[hb]z\M} } } */
+
+/* Test if by-piece overlap compare is enabled and following case is
+   implemented by two overlap word loads and compares.  */
+
+int foo (const char* s1, const char* s2)
+{
+  return __builtin_memcmp (s1, s2, 7) == 0;
+}