codegen: optimize const fields of mutable objects #53484
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vtjnash
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gbaraldi
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For example, we seek to eliminate the gc frame from this function, as observed here: ```julia julia> code_llvm((BitSet,), raw=true) do x; r = x.bits; GC.safepoint(); @inbounds r[1]; end ; Function Signature: var"#3"(Base.BitSet) ; @ REPL[1]:1 within `#3` define swiftcc i64 @"julia_#3_494"(ptr nonnull swiftself %pgcstack, ptr noundef nonnull align 8 dereferenceable(16) %"x::BitSet") #0 !dbg !5 { top: call void @llvm.dbg.declare(metadata ptr %"x::BitSet", metadata !21, metadata !DIExpression()), !dbg !22 %ptls_field = getelementptr inbounds ptr, ptr %pgcstack, i64 2 %ptls_load = load ptr, ptr %ptls_field, align 8, !tbaa !23 %0 = getelementptr inbounds ptr, ptr %ptls_load, i64 2 %safepoint = load ptr, ptr %0, align 8, !tbaa !27 fence syncscope("singlethread") seq_cst %1 = load volatile i64, ptr %safepoint, align 8, !dbg !22 fence syncscope("singlethread") seq_cst ; ┌ @ Base.jl:49 within `getproperty` %"x::BitSet.bits" = load atomic ptr, ptr %"x::BitSet" unordered, align 8, !dbg !29, !tbaa !27, !alias.scope !33, !noalias !36, !nonnull !11, !dereferenceable !41, !align !42 ; └ ; ┌ @ gcutils.jl:253 within `safepoint` %ptls_load4 = load ptr, ptr %ptls_field, align 8, !dbg !43, !tbaa !23 %2 = getelementptr inbounds ptr, ptr %ptls_load4, i64 2, !dbg !43 %safepoint5 = load ptr, ptr %2, align 8, !dbg !43, !tbaa !27 fence syncscope("singlethread") seq_cst, !dbg !43 %3 = load volatile i64, ptr %safepoint5, align 8, !dbg !43 fence syncscope("singlethread") seq_cst, !dbg !43 ; └ ; ┌ @ essentials.jl:892 within `getindex` %4 = load ptr, ptr %"x::BitSet.bits", align 8, !dbg !46, !tbaa !49, !alias.scope !52, !noalias !53 %5 = load i64, ptr %4, align 8, !dbg !46, !tbaa !54, !alias.scope !57, !noalias !58 ret i64 %5, !dbg !46 ; └ } ```
Make this analysis even stronger, using a function from llvm-late-gc-lowering.cpp that implements it more aggressively
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|
@nanosoldier |
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Your benchmark job has completed - possible performance regressions were detected. A full report can be found here. |
vtjnash
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One non-null result here, since I assume that means alloc-opt failed for this: |
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For example, we seek to eliminate the gc frame from this function, as
observed here: