[gcc r15-480] rs6000: Enable overlapped by-pieces operations

[HaoChen Gui]

https://gcc.gnu.org/g:fbd115fe83e96e0796cd8e262ed773b0ba07db81

commit r15-480-gfbd115fe83e96e0796cd8e262ed773b0ba07db81
Author: Haochen Gui <guihaoc@gcc.gnu.org>
Date:   Tue May 14 16:37:06 2024 +0800

    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.

Diff:
---
 gcc/config/rs6000/rs6000.cc                    |  3 +++
 gcc/testsuite/gcc.target/powerpc/block-cmp-9.c | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 117999613d83..e713a1e1d570 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -1776,6 +1776,9 @@ 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 000000000000..f16429c2ffb0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { 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;
+}