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LLVM IR and passes skill for reading compiler IR. Use when analyzing LLVM IR, understanding SSA, pass pipeline order, or running opt on bitcode. Activates on queries about LLVM IR, SSA form, opt passes, llvm-dis, pass pipeline, or reading .ll files.
用 Codex 或 Claude 帮你安装 复制这段 Prompt，粘贴到 Codex、Claude 或其他助手里，让它检查 Skill 页面并帮你完成安装。
基于 SOC 职业分类
| name | llvm-ir-and-passes |
| description | LLVM IR and passes skill for reading compiler IR. Use when analyzing LLVM IR, understanding SSA, pass pipeline order, or running opt on bitcode. Activates on queries about LLVM IR, SSA form, opt passes, llvm-dis, pass pipeline, or reading .ll files. |
Teach agents to read and reason about LLVM IR (SSA, types, terminators), navigate the standard pass pipeline, and use opt/llvm-dis for inspection. Complements skills/compilers/llvm (toolchain) and skills/compiler-internals/llvm-passes (writing plugins) — not merged.
-O2 changed in generated IR; Function in SSA form
define i32 @add(i32 %a, i32 %b) {
entry:
%sum = add i32 %a, %b
ret i32 %sum
}
Key concepts: basic blocks, PHI nodes at merges, typed values (i32, ptr, vectors).
clang -S -emit-llvm -O0 -o foo.ll foo.c
clang -c -emit-llvm -O2 -o foo.bc foo.c
llvm-dis foo.bc -o foo.ll
Clang -O2 roughly runs:
SimplifyCFG → InstCombine → GVN → LICM → LoopVectorize → ...
Inspect with:
opt -passes='default<O2>' -S foo.ll -o foo-opt.ll
opt -passes='default<O2>' -print-passes foo.ll 2>&1 | head
| Pass | Shows |
|---|---|
-passes=print<domtree> | Dominator tree |
-passes=print<loops> | Loop nests |
-passes=print-alias-sets | Alias sets |
opt -passes='print<domtree>' -disable-output foo.ll
merge:
%v = phi i32 [ %a, %then ], [ %b, %else ]
undef and poison in IR model LLVM poison semantics — distinct from C UB but related.
opt -passes='instcombine,simplifycfg' -S foo.ll -o - | diff -u foo.ll -
/llvm-ir-and-passes Explain this PHI node and which pass likely created it
| Symptom | Cause | Fix |
|---|---|---|
| Pass not found | LLVM version rename | opt --print-passes for your build |
| IR mismatch | Different LLVM major | Match clang/opt versions |
| "optnone" blocks opts | -O0 attribute | Compile with -O1+ |
| Huge IR | Inlined headers | -fno-discard-value-names off; filter function |
| Wrong pipeline | Legacy vs NPM | Use -passes= syntax |
skills/compilers/llvm — toolchain overviewskills/compiler-internals/llvm-passes — writing PassPluginsskills/compiler-internals/compiler-optimizations-deep — RA and ISelskills/compiler-internals/compiler-frontend — IR generationskills/rust/rustc-basics — rustc --emit=llvm-irCustom allocator skill for memory allocation strategies. Use when implementing pool/slab/arena allocators, tuning jemalloc/mimalloc, writing Rust GlobalAlloc, or benchmarking allocator performance. Activates on queries about jemalloc, mimalloc, tcmalloc, arena allocator, GlobalAlloc, or fragmentation.
NUMA programming skill for multi-socket memory locality. Use when detecting NUMA topology, binding processes with numactl, using libnuma API, building NUMA-aware data structures, or measuring remote access penalties. Activates on queries about numactl, libnuma, NUMA topology, mbind, lstopo, or remote memory access.
AF_XDP skill for high-performance XDP sockets. Use when creating AF_XDP sockets, configuring UMEM and XSK rings, XDP_REDIRECT programs, copy vs zero-copy mode, or comparing with DPDK. Activates on queries about AF_XDP, xsk_umem, XDP_REDIRECT, libbpf xsk, or zero-copy XDP.
DPDK skill for userspace packet I/O. Use when initializing EAL, configuring PMD drivers, using mbuf pools and rte_ring, setting up huge pages, RSS, or testpmd validation. Activates on queries about DPDK, EAL, rte_eth_rx_burst, hugepages, PMD, or testpmd.
io_uring skill for Linux async I/O. Use when building high-performance servers with liburing, multi-shot operations, provided buffers, fixed files, zero-copy send, or tokio-uring. Activates on queries about io_uring, SQE/CQE, liburing, IORING_OP_PROVIDE_BUFFERS, or io_uring vs epoll.
Bare-metal ADC and DAC skill. Use when configuring analog sampling, DMA-driven ADC, calibration, or DAC output on MCUs. Activates on queries about ADC bare-metal, sampling time, DMA ADC, or DAC channel setup.