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
20 lines
453 B
LLVM
20 lines
453 B
LLVM
; RUN: llc -mtriple=bpfel -mcpu=v1 -filetype=obj -o - %s | llvm-objdump -d - | FileCheck %s
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;
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; Source:
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; int test() {
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; asm volatile("r0 = r0" ::);
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; return 0;
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; }
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; Compilation flag:
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; clang -target bpf -O2 -S -emit-llvm t.c
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; Function Attrs: nounwind
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define dso_local i32 @test() local_unnamed_addr {
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entry:
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tail call void asm sideeffect "r0 = r0", ""()
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ret i32 0
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}
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; CHECK-LABEL: test
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; CHECK: r0 = r0
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; CHECK: r0 = 0
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