Fix a regression in the test for #13432 (#55004)

The test for #13432 is supposed to test a particular codegen path
involving Bottom. It turns out that this code path is regressed on
master, but hidden by the fact that in modern julia, the optimizer can
fold this code path early. Fix the bug and add a variant of the test
that shows the issue on julia master. Note that this is both an
assertion failure and incorrect codegen. This PR addresses both.

src/cgutils.cpp

@@ -1598,7 +1598,7 @@ static bool can_optimize_isa_union(jl_uniontype_t *type)
 // a simple case of emit_isa that is obvious not to include a safe-point
 static Value *emit_exactly_isa(jl_codectx_t &ctx, const jl_cgval_t &arg, jl_datatype_t *dt, bool could_be_null=false)
 {
-    assert(jl_is_concrete_type((jl_value_t*)dt));
+    assert(jl_is_concrete_type((jl_value_t*)dt) || is_uniquerep_Type((jl_value_t*)dt));
     if (arg.TIndex) {
         unsigned tindex = get_box_tindex(dt, arg.typ);
         if (tindex > 0) {
@@ -1621,7 +1621,12 @@ static Value *emit_exactly_isa(jl_codectx_t &ctx, const jl_cgval_t &arg, jl_data
             BasicBlock *postBB = BasicBlock::Create(ctx.builder.getContext(), "post_isa", ctx.f);
             ctx.builder.CreateCondBr(isboxed, isaBB, postBB);
             ctx.builder.SetInsertPoint(isaBB);
-            Value *istype_boxed = ctx.builder.CreateICmpEQ(emit_typeof(ctx, arg.Vboxed, false, true), emit_tagfrom(ctx, dt));
+            Value *istype_boxed = NULL;
+            if (is_uniquerep_Type((jl_value_t*)dt)) {
+                istype_boxed = ctx.builder.CreateICmpEQ(decay_derived(ctx, arg.Vboxed), decay_derived(ctx, literal_pointer_val(ctx, jl_tparam0(dt))));
+            } else {
+                istype_boxed = ctx.builder.CreateICmpEQ(emit_typeof(ctx, arg.Vboxed, false, true), emit_tagfrom(ctx, dt));
+            }
             ctx.builder.CreateBr(postBB);
             isaBB = ctx.builder.GetInsertBlock(); // could have changed
             ctx.builder.SetInsertPoint(postBB);

test/core.jl

@@ -3999,6 +3999,14 @@ end
 end
 @test f13432b(true) == true
 @test f13432b(false) == false
+@noinline function f13432c(x)
+    offset = x ? Base.Bottom : 1
+    # Barrier for inference, so the optimizer cannot optimize this,
+    # but codegen can still see this is a constant
+    return ===(offset, Base.inferencebarrier(Base.Bottom))
+end
+@test f13432c(true) == true
+@test f13432c(false) == false
 
 #13433, read!(::IO, a::Vector{UInt8}) should return a
 mutable struct IO13433 <: IO end