This patch enables the overlap-by-pieces feature of the by-pieces
infrastructure for inlining builtins in case the target has set
riscv_slow_unaligned_access_p to false.

To demonstrate the effect for targets with fast unaligned access,
the following code sequences are generated for a 15-byte memset-zero.

Without overlap_op_by_pieces we get:
  8e:   00053023                sd      zero,0(a0)
  92:   00052423                sw      zero,8(a0)
  96:   00051623                sh      zero,12(a0)
  9a:   00050723                sb      zero,14(a0)

With overlap_op_by_pieces we get:
  7e:   00053023                sd      zero,0(a0)
  82:   000533a3                sd      zero,7(a0)

gcc/ChangeLog:

        * config/riscv/riscv.c (riscv_overlap_op_by_pieces): New function.
        (TARGET_OVERLAP_OP_BY_PIECES_P): Connect to
        riscv_overlap_op_by_pieces.

Signed-off-by: Christoph Muellner <cmuell...@gcc.gnu.org>
---
 gcc/config/riscv/riscv.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/gcc/config/riscv/riscv.c b/gcc/config/riscv/riscv.c
index 576960bb37c..98c76ba657a 100644
--- a/gcc/config/riscv/riscv.c
+++ b/gcc/config/riscv/riscv.c
@@ -5201,6 +5201,14 @@ riscv_slow_unaligned_access (machine_mode, unsigned int)
   return riscv_slow_unaligned_access_p;
 }
 
+/* Implement TARGET_OVERLAP_OP_BY_PIECES_P.  */
+
+static bool
+riscv_overlap_op_by_pieces (void)
+{
+  return !riscv_slow_unaligned_access_p;
+}
+
 /* Implement TARGET_CAN_CHANGE_MODE_CLASS.  */
 
 static bool
@@ -5525,6 +5533,9 @@ riscv_asan_shadow_offset (void)
 #undef TARGET_SLOW_UNALIGNED_ACCESS
 #define TARGET_SLOW_UNALIGNED_ACCESS riscv_slow_unaligned_access
 
+#undef TARGET_OVERLAP_OP_BY_PIECES_P
+#define TARGET_OVERLAP_OP_BY_PIECES_P riscv_overlap_op_by_pieces
+
 #undef TARGET_SECONDARY_MEMORY_NEEDED
 #define TARGET_SECONDARY_MEMORY_NEEDED riscv_secondary_memory_needed
 
-- 
2.31.1

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