Strip IR after front-end steps are done (#1092)

* Strip IR after front-end steps are done

The main feature of this change is to unconditonally strip out the `IRHighLevelDeclDecoration`s in an IR module once the "mandatory" IR passes in the front end have run. This ensures that later IR passes (e.g., code emission) *cannot* rely on AST-level information to get their job done.

Since I was already writing a pass to remove some instructions at the end of the front-end passes, I went ahead and also made the `-obfuscate` flag apply to the front-end IR generation by causing it to strip `IRNameHintDecoration`s while it is doing the other stripping. With this, the main identifying information left in IR modules (other than semantics and entry-point names) is mangled name strings for imported/exported symbols.

A few other things got changes along the way:

* Removed the `.expected` file for one of the tests, where that file seemingly shouldn't have been checked in at all.

* Updated the signature of the DCE pass both so that it doesn't require a back-end compile request (it wasn't using it anyway), and so that it takes some options to decide whether to keep symbols marked `[export(...)]` alive (the front-end wants to keep these, while back-end passes currently need to be able to eliminate them).

* Moved the `obfuscateCode` flag from the back-end compile request to the base class shared between front- and back-end requests, and updated the options and repro logic to set both as needed. An obvious improvement in the future would be to have the front- and back-end requests share these settings by referencing a single common object in the end-to-end case, rather than each having their own copy.

* Removed logic that was keeping layout instructions alive in DCE, even if they weren't used. This seems to have been a vestige of an intermediate step between AST and IR layout.

* fixup: add the new files

1 files changed, 0 insertions, 20 deletions

diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index 89e49816f..31224fde2 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -4040,26 +4040,6 @@ namespace Slang
     {
         for(auto dd : inst->getDecorations())
         {
-            // Certain decorations aren't helpful to appear
-            // in output dumps, so we will only include them
-            // in the "detailed" dumping mode.
-            //
-            // For all other modes, we will check the opcode
-            // and skip selected decorations.
-            //
-            if(context->mode != IRDumpMode::Detailed)
-            {
-                switch(dd->op)
-                {
-                default:
-                    break;
-
-                case kIROp_HighLevelDeclDecoration:
-                case kIROp_LayoutDecoration:
-                    continue;
-                }
-            }
-
             dump(context, "[");
             dumpInstBody(context, dd);
             dump(context, "]\n");