[gcc r14-5923] bpf: Forces __buildin_memcmp not to generate a call upto 1024 bytes.

[gcc r14-5923] bpf: Forces __buildin_memcmp not to generate a call upto 1024 bytes.

[Cupertino Miranda]

https://gcc.gnu.org/g:19cc5857e2cb0fb7c637a35a956f902d44286c2d

commit r14-5923-g19cc5857e2cb0fb7c637a35a956f902d44286c2d
Author: Cupertino Miranda <cupertino.miranda@oracle.com>
Date:   Fri Nov 10 16:42:13 2023 +0000

    bpf: Forces __buildin_memcmp not to generate a call upto 1024 bytes.
    
    This patch forces __builtin_memcmp calls upto data sizes of 1024 to
    become inline in caller.
    This is a requirement by BPF and it mimics the default behaviour of the
    clang BPF implementation.
    
    gcc/ChangeLog:
            * config/bpf/bpf.cc (bpf_use_by_pieces_infrastructure_p): Added
            function to bypass default behaviour.
            * config/bpf/bpf.h (COMPARE_MAX_PIECES): Defined to 1024 bytes.

Diff:
---
 gcc/config/bpf/bpf.cc | 16 ++++++++++++++++
 gcc/config/bpf/bpf.h  |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
index 223a43cbbb3..4bfba289546 100644
--- a/gcc/config/bpf/bpf.cc
+++ b/gcc/config/bpf/bpf.cc
@@ -1117,6 +1117,22 @@ bpf_small_register_classes_for_mode_p (machine_mode mode)
 #define TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P \
   bpf_small_register_classes_for_mode_p
 
+static bool
+bpf_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT size,
+				    unsigned int align ATTRIBUTE_UNUSED,
+				    enum by_pieces_operation op,
+				    bool speed_p)
+{
+  if (op != COMPARE_BY_PIECES)
+    return default_use_by_pieces_infrastructure_p (size, align, op, speed_p);
+
+  return size <= COMPARE_MAX_PIECES;
+}
+
+#undef TARGET_USE_BY_PIECES_INFRASTRUCTURE_P
+#define TARGET_USE_BY_PIECES_INFRASTRUCTURE_P \
+  bpf_use_by_pieces_infrastructure_p
+
 /* Finally, build the GCC target.  */
 
 struct gcc_target targetm = TARGET_INITIALIZER;
diff --git a/gcc/config/bpf/bpf.h b/gcc/config/bpf/bpf.h
index 82702aa7b6b..1f177ec4c4e 100644
--- a/gcc/config/bpf/bpf.h
+++ b/gcc/config/bpf/bpf.h
@@ -489,6 +489,11 @@ enum reg_class
    locations.  */
 #define MOVE_MAX 8
 
+/* Allow upto 1024 bytes moves to occur using by_pieces
+   infrastructure.  This mimics clang behaviour when using
+   __builtin_memcmp.  */
+#define COMPARE_MAX_PIECES 1024
+
 /* An alias for the machine mode for pointers.  */
 #define Pmode DImode