LLVMバージョン6.0.0でC ++コンパイラを使用する場合、次のコード
bool isEven(int n) {
bool ret = true;
for (int i = 0; i < n; i ++) {
ret = !ret;
}
return ret;
}
LLVM IRを放出します
define zeroext i1 @_Z6isEveni(i32) local_unnamed_addr #0 !dbg !7 {
call void @llvm.dbg.value(metadata i32 %0, metadata !14, metadata !DIExpression()), !dbg !18
call void @llvm.dbg.value(metadata i8 1, metadata !15, metadata !DIExpression()), !dbg !19
call void @llvm.dbg.value(metadata i32 0, metadata !16, metadata !DIExpression()), !dbg !20
%2 = icmp slt i32 %0, 1, !dbg !21
%3 = and i32 %0, 1, !dbg !23
%4 = icmp eq i32 %3, 0, !dbg !23
%5 = or i1 %4, %2, !dbg !23
ret i1 %5, !dbg !24
}
declare void @llvm.dbg.value(metadata, metadata, metadata) #1
attributes #0 = { nounwind readnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind readnone speculatable }
参照:https : //godbolt.org/z/oPBFey
これは、次の実装と機能的に同等です。
julia> isEven(n::Int) = rem(n, 2) != 0
isEven (generic function with 1 method)
julia> @code_llvm debuginfo=:none isEven(7)
define i8 @julia_isEven_18796(i64) {
top:
%1 = trunc i64 %0 to i8
%2 = and i8 %1, 1
%3 = xor i8 %2, 1
ret i8 %3
}
julia>
ただし、Juliaに移植された元のC ++実装では、非常に異なるLLVM IRになります。
julia> function isEven(n::Int)
out = true
for i in 0:n-1
out = !out
end
return out
end
isEven (generic function with 1 method)
julia> @code_llvm debuginfo=:none isEven(7)
define i8 @julia_isEven_18793(i64) {
top:
%1 = add i64 %0, -1
%2 = icmp sgt i64 %1, -1
br i1 %2, label %L8.L12_crit_edge, label %L25
L8.L12_crit_edge: ; preds = %top
%min.iters.check = icmp ult i64 %0, 128
br i1 %min.iters.check, label %scalar.ph, label %vector.ph
vector.ph: ; preds = %L8.L12_crit_edge
%n.vec = and i64 %0, -128
br label %vector.body
vector.body: ; preds = %vector.body, %vector.ph
%index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
%vec.phi = phi <32 x i8> [ <i8 1, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>, %vector.ph ], [ %3, %vector.body ]
%vec.phi8 = phi <32 x i8> [ zeroinitializer, %vector.ph ], [ %4, %vector.body ]
%vec.phi9 = phi <32 x i8> [ zeroinitializer, %vector.ph ], [ %5, %vector.body ]
%vec.phi10 = phi <32 x i8> [ zeroinitializer, %vector.ph ], [ %6, %vector.body ]
%3 = xor <32 x i8> %vec.phi, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
%4 = xor <32 x i8> %vec.phi8, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
%5 = xor <32 x i8> %vec.phi9, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
%6 = xor <32 x i8> %vec.phi10, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
%index.next = add i64 %index, 128
%7 = icmp eq i64 %index.next, %n.vec
br i1 %7, label %middle.block, label %vector.body
middle.block: ; preds = %vector.body
%bin.rdx = xor <32 x i8> %vec.phi8, %vec.phi
%bin.rdx14 = xor <32 x i8> %5, %bin.rdx
%bin.rdx15 = xor <32 x i8> %6, %bin.rdx14
%rdx.shuf = shufflevector <32 x i8> %bin.rdx15, <32 x i8> undef, <32 x i32> <i32 16, i32 17, i32 18, i32 19, i32 20, i32 21, i32 22, i32 23, i32 24, i32 25, i32 26, i32 27, i32 28, i32 29, i32 30, i32 31, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
%bin.rdx16 = xor <32 x i8> %bin.rdx15, %rdx.shuf
%rdx.shuf17 = shufflevector <32 x i8> %bin.rdx16, <32 x i8> undef, <32 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
%bin.rdx18 = xor <32 x i8> %bin.rdx16, %rdx.shuf17
%rdx.shuf19 = shufflevector <32 x i8> %bin.rdx18, <32 x i8> undef, <32 x i32> <i32 4, i32 5, i32 6, i32 7, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
%bin.rdx20 = xor <32 x i8> %bin.rdx18, %rdx.shuf19
%rdx.shuf21 = shufflevector <32 x i8> %bin.rdx20, <32 x i8> undef, <32 x i32> <i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
%bin.rdx22 = xor <32 x i8> %bin.rdx20, %rdx.shuf21
%rdx.shuf23 = shufflevector <32 x i8> %bin.rdx22, <32 x i8> undef, <32 x i32> <i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
%bin.rdx24 = xor <32 x i8> %bin.rdx22, %rdx.shuf23
%8 = extractelement <32 x i8> %bin.rdx24, i32 0
%cmp.n = icmp eq i64 %n.vec, %0
br i1 %cmp.n, label %L25, label %scalar.ph
scalar.ph: ; preds = %middle.block, %L8.L12_crit_edge
%bc.resume.val = phi i64 [ %n.vec, %middle.block ], [ 0, %L8.L12_crit_edge ]
%bc.merge.rdx = phi i8 [ %8, %middle.block ], [ 1, %L8.L12_crit_edge ]
br label %L12
L12: ; preds = %L12, %scalar.ph
%value_phi2 = phi i8 [ %bc.merge.rdx, %scalar.ph ], [ %9, %L12 ]
%value_phi3 = phi i64 [ %bc.resume.val, %scalar.ph ], [ %11, %L12 ]
%9 = xor i8 %value_phi2, 1
%10 = icmp eq i64 %value_phi3, %1
%11 = add i64 %value_phi3, 1
br i1 %10, label %L25, label %L12
L25: ; preds = %L12, %middle.block, %top
%value_phi6 = phi i8 [ 1, %top ], [ %9, %L12 ], [ %8, %middle.block ]
ret i8 %value_phi6
}
julia> versioninfo()
Julia Version 1.3.1
Commit 2d5741174c (2019-12-30 21:36 UTC)
Platform Info:
OS: macOS (x86_64-apple-darwin18.6.0)
CPU: Intel(R) Core(TM) i7-7920HQ CPU @ 3.10GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.1 (ORCJIT, skylake)
julia>
Juliaがほぼ同じバージョンのLLVMで基本的に同じコードのC ++コンパイラーと同じIRを生成できない理由を誰かが説明できますか?