1.8 regression: isbitstype does not resolve at compile-time

[maleadt]

MWE:

using GPUCompiler

module TestRuntime
    # dummy methods
    signal_exception() = return
    malloc(sz) = C_NULL
    report_oom(sz) = return
    report_exception(ex) = return
    report_exception_name(ex) = return
    report_exception_frame(idx, func, file, line) = return
end

struct TestCompilerParams <: AbstractCompilerParams end
GPUCompiler.runtime_module(::CompilerJob{<:Any,TestCompilerParams}) = TestRuntime

function kernel(ptr::Ptr{T}, val) where {T}
    if isbitstype(T)
        unsafe_store!(ptr, val, 1)
    end
    return
end

function main()
    source = FunctionSpec(kernel, Tuple{Ptr{Float32}, Float32})
    target = NativeCompilerTarget()
    params = TestCompilerParams()
    job = CompilerJob(target, source, params)

    JuliaContext() do ctx
        println(GPUCompiler.compile(:llvm, job; ctx)[1])
    end
end

isinteractive() || main()

On 1.9:

define void @_Z16julia_kernel_6353PtrI7Float32ES0_(i64 zeroext %0, float %1) local_unnamed_addr #0 !dbg !5 {
top:
  %2 = load i8, i8* inttoptr (i64 4914551176 to i8*), align 8, !dbg !7, !tbaa !14
  %3 = and i8 %2, 8, !dbg !18
  %.not = icmp eq i8 %3, 0, !dbg !21
  br i1 %.not, label %L7, label %L6, !dbg !13

L6:                                               ; preds = %top
  %4 = inttoptr i64 %0 to float*, !dbg !24
  store float %1, float* %4, align 1, !dbg !24, !tbaa !28
  br label %L7, !dbg !24

L7:                                               ; preds = %L6, %top
  ret void, !dbg !30
}

... which is Really Bad, since it's leaking CPU values into the GPU IR.

For reference, on 1.8:

define void @_Z16julia_kernel_4963PtrI7Float32ES0_(i64 zeroext %0, float %1) local_unnamed_addr #0 !dbg !5 {
top:
  %2 = inttoptr i64 %0 to float*, !dbg !7
  store float %1, float* %2, align 1, !dbg !7, !tbaa !11
  ret void, !dbg !15
}

Enabling inference remarks gives:

┌ Debug: Inference remark during GPU compilation of MethodInstance for isbitstype(::Type{Float32}): [constprop] Disabled by function heuristic
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for kernel(::Ptr{Float32}, ::Float32): [constprop] Disabled by argument and rettype heuristics
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for unsafe_store!(::Ptr{Float32}, ::Float32, ::Int64): [constprop] Disabled by argument and rettype heuristics
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for Int64(::Int64): [constprop] Disabled by argument and rettype heuristics
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for unsafe_store!(::Ptr{Float32}, ::Float32, ::Int64): [constprop] Disabled by argument and rettype heuristics
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for unsafe_store!(::Ptr{Float32}, ::Float32, ::Int64): [constprop] Disabled by argument and rettype heuristics
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35
┌ Debug: Inference remark during GPU compilation of MethodInstance for kernel(::Ptr{Float32}, ::Float32): Call result type was widened because the return value is unused
└ @ GPUCompiler ~/Julia/pkg/GPUCompiler/src/utils.jl:35

Const-prop of isbitstype being disabled seems crucial here. I wonder if this has anything to do with the fix to JuliaLang/julia@4846fbb (cc @aviatesk).

[vchuravy]

The failure for allocatedinline #302 (comment) is potentially related.

[maleadt]

Defining isoverlayed(::OverlayMethodTable) = false makes this infer properly again, so this is definitely related to JuliaLang/julia#44224

[aviatesk]

I will work on it today.

[aviatesk]

JuliaLang/julia#44515 will beat this out.

[maleadt]

Thanks! Tested the PR, and works great :-)

[maleadt]

And yes this also fixes #302 (comment)