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
69 lines
1.9 KiB
LLVM
69 lines
1.9 KiB
LLVM
; RUN: llc -O2 --march=bpfel -mcpu=v1 %s -o - | FileCheck %s
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; Generated from the following C code:
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;
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; #define __bpf_fastcall __attribute__((bpf_fastcall))
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;
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; void bar(void) __bpf_fastcall;
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; void buz(long i, long j);
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;
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; void foo(long i, long j, long k, long l) {
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; bar();
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; if (k > 42l)
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; buz(i, 1);
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; else
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; buz(1, j);
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; }
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;
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; Using the following command:
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;
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; clang --target=bpf -emit-llvm -O2 -S -o - t.c
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;
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; (unnecessary attrs removed maually)
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; Check that function marked with bpf_fastcall does not clobber R1-R5.
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; Use R1 in one branch following call and R2 in another branch following call.
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define dso_local void @foo(i64 noundef %i, i64 noundef %j, i64 noundef %k, i64 noundef %l) {
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entry:
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tail call void @bar() #0
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%cmp = icmp sgt i64 %k, 42
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br i1 %cmp, label %if.then, label %if.else
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if.then:
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tail call void @buz(i64 noundef %i, i64 noundef 1)
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br label %if.end
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if.else:
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tail call void @buz(i64 noundef 1, i64 noundef %j)
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br label %if.end
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if.end:
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ret void
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}
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; CHECK: foo: # @foo
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; CHECK: # %bb.0: # %entry
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; CHECK-NEXT: *(u64 *)(r10 - 8) = r1
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; CHECK-NEXT: *(u64 *)(r10 - 16) = r2
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; CHECK-NEXT: *(u64 *)(r10 - 24) = r3
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; CHECK-NEXT: call bar
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; CHECK-NEXT: r3 = *(u64 *)(r10 - 24)
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; CHECK-NEXT: r2 = *(u64 *)(r10 - 16)
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; CHECK-NEXT: r1 = *(u64 *)(r10 - 8)
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; CHECK-NEXT: r4 = 43
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; CHECK-NEXT: if r4 s> r3 goto [[ELSE:.*]]
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; CHECK-NEXT: # %bb.1: # %if.then
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; CHECK-NEXT: r2 = 1
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; CHECK-NEXT: goto [[END:.*]]
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; CHECK-NEXT: [[ELSE]]: # %if.else
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; CHECK-NEXT: r1 = 1
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; CHECK-NEXT: [[END]]: # %if.end
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; CHECK-NEXT: call buz
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; CHECK-NEXT: exit
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declare dso_local void @bar() #0
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declare dso_local void @buz(i64 noundef, i64 noundef)
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attributes #0 = { "bpf_fastcall" }
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