fix #32843, codegen attempting typeof(NULL) for some union tags (#40365)

also fixes part of #40065

Author: JeffBezanson

src/cgutils.cpp

@@ -2472,6 +2472,27 @@ static Value *compute_box_tindex(jl_codectx_t &ctx, Value *datatype, jl_value_t
     return tindex;
 }
 
+// Returns typeof(v), or null if v is a null pointer at run time.
+// This is used when the value might have come from an undefined variable,
+// yet we try to read its type to compute a union index when moving the value.
+static Value *emit_typeof_or_null(jl_codectx_t &ctx, Value *v)
+{
+    BasicBlock *nonnull = BasicBlock::Create(jl_LLVMContext, "nonnull", ctx.f);
+    BasicBlock *postBB = BasicBlock::Create(jl_LLVMContext, "postnull", ctx.f);
+    Value *isnull = ctx.builder.CreateICmpEQ(v, Constant::getNullValue(v->getType()));
+    ctx.builder.CreateCondBr(isnull, postBB, nonnull);
+    BasicBlock *entry = ctx.builder.GetInsertBlock();
+    ctx.builder.SetInsertPoint(nonnull);
+    Value *typof = emit_typeof(ctx, v);
+    ctx.builder.CreateBr(postBB);
+    nonnull = ctx.builder.GetInsertBlock(); // could have changed
+    ctx.builder.SetInsertPoint(postBB);
+    PHINode *ti = ctx.builder.CreatePHI(typof->getType(), 2);
+    ti->addIncoming(Constant::getNullValue(typof->getType()), entry);
+    ti->addIncoming(typof, nonnull);
+    return ti;
+}
+
 // get the runtime tindex value, assuming val is already converted to type typ if it has a TIndex
 static Value *compute_tindex_unboxed(jl_codectx_t &ctx, const jl_cgval_t &val, jl_value_t *typ)
 {
@@ -2482,9 +2503,12 @@ static Value *compute_tindex_unboxed(jl_codectx_t &ctx, const jl_cgval_t &val, j
 
     if (val.TIndex)
         return ctx.builder.CreateAnd(val.TIndex, ConstantInt::get(T_int8, 0x7f));
-    if (val.isboxed)
-        return compute_box_tindex(ctx, emit_typeof_boxed(ctx, val), val.typ, typ);
-    return compute_box_tindex(ctx, emit_typeof_boxed(ctx, val), val.typ, typ);
+    Value *typof;
+    if (val.isboxed && !jl_is_concrete_type(val.typ) && !jl_is_type_type(val.typ))
+        typof = emit_typeof_or_null(ctx, val.V);
+    else
+        typof = emit_typeof_boxed(ctx, val);
+    return compute_box_tindex(ctx, typof, val.typ, typ);
 }
 
 static void union_alloca_type(jl_uniontype_t *ut,

src/codegen.cpp

@@ -1504,11 +1504,13 @@ static jl_cgval_t convert_julia_type_union(jl_codectx_t &ctx, const jl_cgval_t &
             // actually need it.
             Value *union_box_dt = NULL;
             BasicBlock *union_isaBB = NULL;
+            BasicBlock *post_union_isaBB = NULL;
             auto maybe_setup_union_isa = [&]() {
                 if (!union_isaBB) {
                     union_isaBB = BasicBlock::Create(jl_LLVMContext, "union_isa", ctx.f);
                     ctx.builder.SetInsertPoint(union_isaBB);
-                    union_box_dt = emit_typeof(ctx, v.Vboxed);
+                    union_box_dt = emit_typeof_or_null(ctx, v.Vboxed);
+                    post_union_isaBB = ctx.builder.GetInsertBlock();
                 }
             };
 
@@ -1540,7 +1542,7 @@ static jl_cgval_t convert_julia_type_union(jl_codectx_t &ctx, const jl_cgval_t &
                 ctx.builder.SetInsertPoint(postBB);
                 PHINode *tindex_phi = ctx.builder.CreatePHI(T_int8, 2);
                 tindex_phi->addIncoming(new_tindex, currBB);
-                tindex_phi->addIncoming(union_box_tindex, union_isaBB);
+                tindex_phi->addIncoming(union_box_tindex, post_union_isaBB);
                 new_tindex = tindex_phi;
             }
         }

test/compiler/codegen.jl

@@ -553,3 +553,11 @@ end
     end
     @test occursin("llvm.julia.gc_preserve_begin", get_llvm(f4, Tuple{Bool}, true, false, false))
 end
+
+# issue #32843
+function f32843(vals0, v)
+    (length(vals0) > 1) && (vals = v[1])
+    (length(vals0) == 1 && vals0[1]==1) && (vals = 1:2)
+    vals
+end
+@test_throws UndefVarError f32843([6], Vector[[1]])