std.debug.SelfInfo: remove shared logic

There were only a few dozen lines of common logic, and they frankly
introduced more complexity than they eliminated. Instead, let's accept
that the implementations of `SelfInfo` are all pretty different and want
to track different state. This probably fixes some synchronization and
memory bugs by simplifying a bunch of stuff. It also improves the DWARF
unwind cache, making it around twice as fast in a debug build with the
self-hosted x86_64 backend, because we no longer have to redundantly go
through the hashmap lookup logic to find the module. Unwinding on
Windows will also see a slight performance boost from this change,
because `RtlVirtualUnwind` does not need to know the module whatsoever,
so the old `SelfInfo` implementation was doing redundant work. Lastly,
this makes it even easier to implement `SelfInfo` on freestanding
targets; there is no longer a need to emulate a real module system,
since the user controls the whole implementation!

There are various other small refactors here in the `SelfInfo`
implementations as well as in the DWARF unwinding logic. This change
turned out to make a lot of stuff simpler!

1 files changed, 11 insertions, 9 deletions

diff --git a/lib/std/debug/Dwarf/Unwind.zig b/lib/std/debug/Dwarf/Unwind.zig
index 8c4c1a19e6..d351c0421e 100644
--- a/lib/std/debug/Dwarf/Unwind.zig
+++ b/lib/std/debug/Dwarf/Unwind.zig
@@ -530,16 +530,18 @@ pub fn prepare(
     };
     if (saw_terminator != expect_terminator) return bad();
 
-    std.mem.sortUnstable(SortedFdeEntry, fde_list.items, {}, struct {
-        fn lessThan(ctx: void, a: SortedFdeEntry, b: SortedFdeEntry) bool {
-            ctx;
-            return a.pc_begin < b.pc_begin;
-        }
-    }.lessThan);
+    if (need_lookup) {
+        std.mem.sortUnstable(SortedFdeEntry, fde_list.items, {}, struct {
+            fn lessThan(ctx: void, a: SortedFdeEntry, b: SortedFdeEntry) bool {
+                ctx;
+                return a.pc_begin < b.pc_begin;
+            }
+        }.lessThan);
 
-    // This temporary is necessary to avoid an RLS footgun where `lookup` ends up non-null `undefined` on OOM.
-    const final_fdes = try fde_list.toOwnedSlice(gpa);
-    unwind.lookup = .{ .sorted_fdes = final_fdes };
+        // This temporary is necessary to avoid an RLS footgun where `lookup` ends up non-null `undefined` on OOM.
+        const final_fdes = try fde_list.toOwnedSlice(gpa);
+        unwind.lookup = .{ .sorted_fdes = final_fdes };
+    }
 }
 
 fn findCie(unwind: *const Unwind, offset: u64) ?*const CommonInformationEntry {