mips, bpf: Optimize loading of 64-bit constants

This patch shaves off a few instructions when loading sparse 64-bit
constants to register. The change is covered by additional tests in
lib/test_bpf.c.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211007142828.634182-1-johan.almbladh@anyfinetworks.com

diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c
index 1f1f7b8..815ade7 100644 (file)
--- a/arch/mips/net/bpf_jit_comp64.c
+++ b/arch/mips/net/bpf_jit_comp64.c
@@ -131,19 +131,25 @@ static void emit_mov_i64(struct jit_context *ctx, u8 dst, u64 imm64)
                emit(ctx, ori, dst, dst, (u16)imm64 & 0xffff);
        } else {
                u8 acc = MIPS_R_ZERO;
+               int shift = 0;
                int k;
 
                for (k = 0; k < 4; k++) {
                        u16 half = imm64 >> (48 - 16 * k);
 
                        if (acc == dst)
-                               emit(ctx, dsll, dst, dst, 16);
+                               shift += 16;
 
                        if (half) {
+                               if (shift)
+                                       emit(ctx, dsll_safe, dst, dst, shift);
                                emit(ctx, ori, dst, acc, half);
                                acc = dst;
+                               shift = 0;
                        }
                }
+               if (shift)
+                       emit(ctx, dsll_safe, dst, dst, shift);
        }
        clobber_reg(ctx, dst);
 }