6c412b6c6f
In [1], a few new insns are proposed to expand BPF ISA to
. fixing the limitation of existing insn (e.g., 16bit jmp offset)
. adding new insns which may improve code quality
(sign_ext_ld, sign_ext_mov, st)
. feature complete (sdiv, smod)
. better user experience (bswap)
This patch implemented insn encoding for
. sign-extended load
. sign-extended mov
. sdiv/smod
. bswap insns
. unconditional jump with 32bit offset
The new bswap insns are generated under cpu=v4 for __builtin_bswap.
For cpu=v3 or earlier, for __builtin_bswap, be or le insns are generated
which is not intuitive for the user.
To support 32-bit branch offset, a 32-bit ja (JMPL) insn is implemented.
For conditional branch which is beyond 16-bit offset, llvm will do
some transformation 'cond_jmp' -> 'cond_jmp + jmpl' to simulate 32bit
conditional jmp. See BPFMIPeephole.cpp for details. The algorithm is
hueristic based. I have tested bpf selftest pyperf600 with unroll account
600 which can indeed generate 32-bit jump insn, e.g.,
13: 06 00 00 00 9b cd 00 00 gotol +0xcd9b <LBB0_6619>
Eduard is working on to add 'st' insn to cpu=v4.
A list of llc flags:
disable-ldsx, disable-movsx, disable-bswap,
disable-sdiv-smod, disable-gotol
can be used to disable a particular insn for cpu v4.
For example, user can do:
llc -march=bpf -mcpu=v4 -disable-movsx t.ll
to enable cpu v4 without movsx insns.
References:
[1] https://lore.kernel.org/bpf/4bfe98be-5333-1c7e-2f6d-42486c8ec039@meta.com/
Differential Revision: https://reviews.llvm.org/D144829
105 lines
3.7 KiB
LLVM
105 lines
3.7 KiB
LLVM
; RUN: llc -march=bpfel -mcpu=v4 -verify-machineinstrs -show-mc-encoding < %s | FileCheck %s
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; Source:
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; int f1(char *p) {
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; return *p;
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; }
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; int f2(short *p) {
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; return *p;
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; }
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; int f3(int *p) {
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; return *p;
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; }
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; long f4(char *p) {
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; return *p;
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; }
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; long f5(short *p) {
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; return *p;
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; }
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; long f6(int *p) {
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; return *p;
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; }
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; long f7(long *p) {
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; return *p;
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; }
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; Compilation flags:
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; clang -target bpf -O2 -S -emit-llvm t.c
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i32 @f1(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i8, ptr %p, align 1, !tbaa !3
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%conv = sext i8 %0 to i32
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ret i32 %conv
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}
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; CHECK: r0 = *(s8 *)(r1 + 0) # encoding: [0x91,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i32 @f2(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i16, ptr %p, align 2, !tbaa !6
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%conv = sext i16 %0 to i32
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ret i32 %conv
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}
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; CHECK: r0 = *(s16 *)(r1 + 0) # encoding: [0x89,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i32 @f3(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i32, ptr %p, align 4, !tbaa !8
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ret i32 %0
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}
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; CHECK: w0 = *(u32 *)(r1 + 0) # encoding: [0x61,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i64 @f4(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i8, ptr %p, align 1, !tbaa !3
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%conv = sext i8 %0 to i64
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ret i64 %conv
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}
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; CHECK: r0 = *(s8 *)(r1 + 0) # encoding: [0x91,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i64 @f5(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i16, ptr %p, align 2, !tbaa !6
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%conv = sext i16 %0 to i64
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ret i64 %conv
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}
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; CHECK: r0 = *(s16 *)(r1 + 0) # encoding: [0x89,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i64 @f6(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i32, ptr %p, align 4, !tbaa !8
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%conv = sext i32 %0 to i64
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ret i64 %conv
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}
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; CHECK: r0 = *(s32 *)(r1 + 0) # encoding: [0x81,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read)
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define dso_local i64 @f7(ptr nocapture noundef readonly %p) local_unnamed_addr #0 {
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entry:
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%0 = load i64, ptr %p, align 8, !tbaa !10
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ret i64 %0
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}
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; CHECK: r0 = *(u64 *)(r1 + 0) # encoding: [0x79,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read) "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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!llvm.module.flags = !{!0, !1}
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!llvm.ident = !{!2}
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!0 = !{i32 1, !"wchar_size", i32 4}
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!1 = !{i32 7, !"frame-pointer", i32 2}
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!2 = !{!"clang version 17.0.0 (https://github.com/llvm/llvm-project.git 1bf3221bf1e35d953a0b6783bc6e694cb9b0ceae)"}
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!3 = !{!4, !4, i64 0}
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!4 = !{!"omnipotent char", !5, i64 0}
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!5 = !{!"Simple C/C++ TBAA"}
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!6 = !{!7, !7, i64 0}
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!7 = !{!"short", !4, i64 0}
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!8 = !{!9, !9, i64 0}
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!9 = !{!"int", !4, i64 0}
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!10 = !{!11, !11, i64 0}
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!11 = !{!"long", !4, i64 0}
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