On Thu, Jan 30, 2020 at 03:34:27PM -0800, John Fastabend wrote:
>
> diff --git a/llvm/lib/Target/BPF/BPFInstrInfo.td b/llvm/lib/Target/BPF/BPFInstrInfo.td
> index 0f39294..a187103 100644
> --- a/llvm/lib/Target/BPF/BPFInstrInfo.td
> +++ b/llvm/lib/Target/BPF/BPFInstrInfo.td
> @@ -733,7 +733,7 @@ def : Pat<(i64 (sext GPR32:$src)),
> (SRA_ri (SLL_ri (MOV_32_64 GPR32:$src), 32), 32)>;
>
> def : Pat<(i64 (zext GPR32:$src)),
> - (SRL_ri (SLL_ri (MOV_32_64 GPR32:$src), 32), 32)>;
> + (MOV_32_64 GPR32:$src)>;
That's good optimization and 32-bit zero-extend after mov32 is not x86
specific. It's mandatory on all archs.
But I won't solve this problem. There are both signed and unsigned extensions
in that program. The one that breaks is _singed_ one and it cannot be optimized
into any other instruction by llvm.
Hence the proposal to do pseudo insn for it and upgrade to uapi later.
llvm-objdump -S test_get_stack_rawtp.o
; usize = bpf_get_stack(ctx, raw_data, max_len, BPF_F_USER_STACK);
52: 85 00 00 00 43 00 00 00 call 67
53: b7 02 00 00 00 00 00 00 r2 = 0
54: bc 08 00 00 00 00 00 00 w8 = w0
; if (usize < 0)
55: bc 81 00 00 00 00 00 00 w1 = w8
56: 67 01 00 00 20 00 00 00 r1 <<= 32
57: c7 01 00 00 20 00 00 00 r1 s>>= 32
58: 6d 12 1a 00 00 00 00 00 if r2 s> r1 goto +26 <LBB0_6>
56 and 57 are the shifts.
