fix missing layout allocation (#42035)

Fixes #41503

(cherry picked from commit 10755f7)

Author: vtjnash

src/jltypes.c

@@ -1547,9 +1547,8 @@ static jl_value_t *inst_datatype_inner(jl_datatype_t *dt, jl_svec_t *p, jl_value
     // leading to incorrect layouts and data races (#40050: the A{T} should be
     // an isbitstype singleton of size 0)
     if (cacheable) {
-        if (dt->layout == NULL && !jl_is_primitivetype(dt) && ndt->types != NULL && ndt->isconcretetype) {
+        if (ndt->layout == NULL && ndt->types != NULL && ndt->isconcretetype)
             jl_compute_field_offsets(ndt);
-        }
         jl_cache_type_(ndt);
         JL_UNLOCK(&typecache_lock); // Might GC
     }

test/compiler/codegen.jl

@@ -594,6 +594,14 @@ f41438(y) = y[].x
 @test f41438(Ref{A41438}(A41438(C_NULL))) === C_NULL
 @test f41438(Ref{B41438}(B41438(C_NULL))) === C_NULL
 
+const S41438 = Pair{Any, Ptr{T}} where T
+g41438() = Array{S41438,1}(undef,1)[1].first
+get_llvm(g41438, ()); # cause allocation of layout
+@test S41438.body.layout != C_NULL
+@test !Base.datatype_pointerfree(S41438.body)
+@test S41438{Int}.layout != C_NULL
+@test !Base.datatype_pointerfree(S41438{Int})
+
 # issue #41157
 f41157(a, b) = a[1] = b[1]
 @test_throws BoundsError f41157(Tuple{Int}[], Tuple{Union{}}[])