Document and clean up CodegenParams (#51140)

- Add documentation to CodegenParams fields per request in #51123
- Fix compare_cgparams which hadn't been updated for recent additions
- Remove unused and untested generic_context

The latter was a codegen option that I added, but eventually ended up
not using anywhere, so remove it for the time being. That said, I may
end up in a situation where I need it again in the very near future, so
I may end up eating my words here, but if I need to put it back, I'll
include a test at least ;).

base/reflection.jl

@@ -1212,33 +1212,98 @@ default_debug_info_kind() = unsafe_load(cglobal(:jl_default_debug_info_kind, Cin
 
 # this type mirrors jl_cgparams_t (documented in julia.h)
 struct CodegenParams
+    """
+    If enabled, generate the necessary code to support the --track-allocations
+    command line flag to julia itself. Note that the option itself does not enable
+    allocation tracking. Rather, it merely generates the support code necessary
+    to perform allocation tracking if requested by the command line option.
+    """
     track_allocations::Cint
+
+    """
+    If enabled, generate the necessary code to support the --code-coverage
+    command line flag to julia itself. Note that the option itself does not enable
+    code coverage. Rather, it merely generates the support code necessary
+    to code coverage if requested by the command line option.
+    """
     code_coverage::Cint
+
+    """
+    If enabled, force the compiler to use the specialized signature
+    for all generated functions, whenever legal. If disabled, the choice is made
+    heuristically and specsig is only used when deemed profitable.
+    """
     prefer_specsig::Cint
+
+    """
+    If enabled, enable emission of `.debug_names` sections.
+    """
     gnu_pubnames::Cint
+
+    """
+    Controls what level of debug info to emit. Currently supported values are:
+    - 0: no debug info
+    - 1: full debug info
+    - 2: Line tables only
+    - 3: Debug directives only
+
+    The integer values currently match the llvm::DICompilerUnit::DebugEmissionKind enum,
+    although this is not guaranteed.
+    """
     debug_info_kind::Cint
+
+    """
+    If enabled, generate a GC safepoint at the entry to every function. Emitting
+    these extra safepoints can reduce the amount of time that other threads are
+    waiting for the currently running thread to reach a safepoint. The cost for
+    a safepoint is small, but non-zero. The option is enabled by default.
+    """
     safepoint_on_entry::Cint
+
+    """
+    If enabled, add an implicit argument to each function call that is used to
+    pass down the current task local state pointer. This argument is passed
+    using the `swiftself` convention, which in the ordinary case means that the
+    pointer is kept in a register and accesses are thus very fast. If this option
+    is disabled, the task local state pointer must be loaded from thread local
+    stroage, which incurs a small amount of additional overhead. The option is enabled by
+    default.
+    """
     gcstack_arg::Cint
+
+    """
+    If enabled, use the Julia PLT mechanism to support lazy-resolution of `ccall`
+    targets. The option may be disabled for use in environments where the julia
+    runtime is unavailable, but is otherwise recommended to be enabled, even if
+    lazy resolution is not required, as the Julia PLT mechanism may have superior
+    performance compared to the native platform mechanism. The options is enabled by default.
+    """
     use_jlplt::Cint
 
-    lookup::Ptr{Cvoid}
+    """
+    A pointer of type
 
-    generic_context::Any
+    typedef jl_value_t *(*jl_codeinstance_lookup_t)(jl_method_instance_t *mi JL_PROPAGATES_ROOT,
+    size_t min_world, size_t max_world);
+
+    that may be used by external compilers as a callback to look up the code instance corresponding
+    to a particular method instance.
+    """
+    lookup::Ptr{Cvoid}
 
     function CodegenParams(; track_allocations::Bool=true, code_coverage::Bool=true,
                    prefer_specsig::Bool=false,
                    gnu_pubnames=true, debug_info_kind::Cint = default_debug_info_kind(),
                    safepoint_on_entry::Bool=true,
                    gcstack_arg::Bool=true, use_jlplt::Bool=true,
-                   lookup::Ptr{Cvoid}=unsafe_load(cglobal(:jl_rettype_inferred_addr, Ptr{Cvoid})),
-                   generic_context = nothing)
+                   lookup::Ptr{Cvoid}=unsafe_load(cglobal(:jl_rettype_inferred_addr, Ptr{Cvoid})))
         return new(
             Cint(track_allocations), Cint(code_coverage),
             Cint(prefer_specsig),
             Cint(gnu_pubnames), debug_info_kind,
             Cint(safepoint_on_entry),
             Cint(gcstack_arg), Cint(use_jlplt),
-            lookup, generic_context)
+            lookup)
     end
 end
 

src/cgutils.cpp

@@ -4146,8 +4146,10 @@ static int compare_cgparams(const jl_cgparams_t *a, const jl_cgparams_t *b)
            (a->prefer_specsig == b->prefer_specsig) &&
            (a->gnu_pubnames == b->gnu_pubnames) &&
            (a->debug_info_kind == b->debug_info_kind) &&
-           (a->lookup == b->lookup) &&
-           (a->generic_context == b->generic_context);
+           (a->safepoint_on_entry == b->safepoint_on_entry) &&
+           (a->gcstack_arg == b->gcstack_arg) &&
+           (a->use_jlplt == b->use_jlplt) &&
+           (a->lookup == b->lookup);
 }
 #endif
 

src/codegen.cpp

@@ -1366,8 +1366,7 @@ extern "C" {
         /* safepoint_on_entry */ 1,
         /* gcstack_arg */ 1,
         /* use_jlplt*/ 1,
-        /* lookup */ jl_rettype_inferred_addr,
-        /* generic_context */ NULL };
+        /* lookup */ jl_rettype_inferred_addr };
 }
 
 
@@ -4632,15 +4631,11 @@ static jl_cgval_t emit_call(jl_codectx_t &ctx, jl_expr_t *ex, jl_value_t *rt, bo
         return emit_intrinsic(ctx, fi, args, nargs - 1);
     }
 
-    jl_value_t *context = ctx.params->generic_context == jl_nothing ? nullptr : ctx.params->generic_context;
-    size_t n_generic_args = nargs + (context ? 1 : 0);
+    size_t n_generic_args = nargs;
 
     SmallVector<jl_cgval_t> generic_argv(n_generic_args);
     jl_cgval_t *argv = generic_argv.data();
-    if (context) {
-        generic_argv[0] = mark_julia_const(ctx, context);
-        argv = &generic_argv[1];
-    }
+
     argv[0] = f;
     for (size_t i = 1; i < nargs; ++i) {
         argv[i] = emit_expr(ctx, args[i]);
@@ -9304,7 +9299,6 @@ extern "C" void jl_init_llvm(void)
 {
     jl_page_size = jl_getpagesize();
     jl_default_debug_info_kind = (int) DICompileUnit::DebugEmissionKind::FullDebug;
-    jl_default_cgparams.generic_context = jl_nothing;
 
     InitializeNativeTarget();
     InitializeNativeTargetAsmPrinter();

src/julia.h

@@ -2381,10 +2381,6 @@ typedef struct {
 
     // Cache access. Default: jl_rettype_inferred.
     jl_codeinstance_lookup_t lookup;
-
-    // If not `nothing`, rewrite all generic calls to call
-    // generic_context(f, args...) instead of f(args...).
-    jl_value_t *generic_context;
 } jl_cgparams_t;
 extern JL_DLLEXPORT int jl_default_debug_info_kind;