7852ebc088
Before llvm20, (void)__sync_fetch_and_add(...) always generates locked xadd insns. In linux kernel upstream discussion [1], it is found that for arm64 architecture, the original semantics of (void)__sync_fetch_and_add(...), i.e., __atomic_fetch_add(...), is preferred in order for jit to emit proper native barrier insns. In llvm commits [2] and [3], (void)__sync_fetch_and_add(...) will generate the following insns: - for cpu v1/v2: locked xadd insns to keep backward compatibility - for cpu v3/v4: __atomic_fetch_add() insns To ensure proper barrier semantics for (void)__sync_fetch_and_add(...), cpu v3/v4 is recommended. This patch enables cpu=v3 as the default cpu version. For users wanting to use cpu v1, -mcpu=v1 needs to be explicitly added to clang/llc command line. [1] https://lore.kernel.org/bpf/ZqqiQQWRnz7H93Hc@google.com/T/#mb68d67bc8f39e35a0c3db52468b9de59b79f021f [2] https://github.com/llvm/llvm-project/pull/101428 [3] https://github.com/llvm/llvm-project/pull/106494
42 lines
1.2 KiB
LLVM
42 lines
1.2 KiB
LLVM
; REQUIRES: x86_64-linux
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; RUN: llc < %s -march=bpfel -mcpu=v1 -verify-machineinstrs | FileCheck --check-prefix=CHECK-EL %s
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; RUN: llc < %s -march=bpfeb -mcpu=v1 -verify-machineinstrs | FileCheck --check-prefix=CHECK-EB %s
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;
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; This test requires little-endian host, so we specific x86_64-linux here.
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; Source code:
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; struct test_t1 {
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; char a;
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; int b, c, d;
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; };
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;
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; struct test_t1 g;
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; int test()
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; {
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; struct test_t1 t1 = {.a = 1};
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; g = t1;
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; return 0;
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; }
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%struct.test_t1 = type { i8, i32, i32, i32 }
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@test.t1 = private unnamed_addr constant %struct.test_t1 { i8 1, i32 0, i32 0, i32 0 }, align 4
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@g = common local_unnamed_addr global %struct.test_t1 zeroinitializer, align 4
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; Function Attrs: nounwind
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define i32 @test() local_unnamed_addr #0 {
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entry:
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tail call void @llvm.memcpy.p0.p0.i64(ptr align 4 @g, ptr align 4 @test.t1, i64 16, i1 false)
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; CHECK-EL: r2 = 1
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; CHECK-EL: *(u32 *)(r1 + 0) = r2
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; CHECK-EB: r2 = 16777216
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; CHECK-EB: *(u32 *)(r1 + 0) = r2
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ret i32 0
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}
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; CHECK-EL: .section .rodata.cst16,"aM",@progbits,16
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; CHECK-EB: .section .rodata.cst16,"aM",@progbits,16
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declare void @llvm.memcpy.p0.p0.i64(ptr nocapture writeonly, ptr nocapture readonly, i64, i1) #1
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attributes #0 = { nounwind }
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attributes #1 = { argmemonly nounwind }
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