Work on IR-based cross-compilation (#222)

There are two big changes here:

- Add logic during the initial IR cloning pass for an entry point + target that tries to pick the best possible version of any target-overloaded function. This allows us to pick the intrinsic version of `saturate()` when compiling for HLSL output, but then pick the non-intrinsic version (that is implemented in terms of `clamp()`) when targetting GLSL.

- Add an initial specialization pass that tries to deal with generics. This required some fixing work to IR generation, so that we correctly generate explicit operations to specialize a generic for specific types (this is currently implemented as a `specialize` instruction that takes the generic to specialize plus a declaration-reference that represents the specialized form). With that work in place, we can scan for `specialize` instructions inside of non-generic functions, and use them to trigger generation of specialized code. We rely on the name-mangling scheme to help us find pre-existing specializations when possible.

There are also a bunch of cleanups encountered along the way:

- Don't use the explicit `layout(offset=...)` for uniforms, because it isn't supported by all current drivers. For now we will just assume that our layout rules compute the same values that the driver would for un-marked-up code. We can come back later and try to implement a workaround in the cases where this doesn't apply (e.g., by re-running the layout logic as part of emission, and dropping layout modifiers from variables that don't need explicit layout).

- Fix some issues in IR dump printing so that we print function declarations more nicely.

- Testing: print out failing pixel when image-diff fails

1 files changed, 11 insertions, 2 deletions

diff --git a/source/slang/ir.h b/source/slang/ir.h
index ecc77dbc4..2477c987f 100644
--- a/source/slang/ir.h
+++ b/source/slang/ir.h
@@ -12,6 +12,7 @@
 namespace Slang {
 
 class   Decl;
+class   GenericDecl;
 class   FuncType;
 class   Layout;
 class   Type;
@@ -98,6 +99,7 @@ enum IRDecorationOp : uint16_t
     kIRDecorationOp_HighLevelDecl,
     kIRDecorationOp_Layout,
     kIRDecorationOp_LoopControl,
+    kIRDecorationOp_Target,
 };
 
 // A "decoration" that gets applied to an instruction.
@@ -197,6 +199,11 @@ struct IRInst : IRValue
     // Remove this instruction from its parent block,
     // and then destroy it (it had better have no uses!)
     void removeAndDeallocate();
+
+    // Clear out the arguments of this instruction,
+    // so that we don't appear on the list of uses
+    // for those values.
+    void removeArguments();
 };
 
 typedef int64_t IRIntegerValue;
@@ -321,8 +328,10 @@ struct IRFunc : IRGlobalValue
     // The type of the IR-level function
     IRFuncType* getType() { return (IRFuncType*) type.Ptr(); }
 
-    // Any generic parameters this function has
-    List<RefPtr<Decl>> genericParams;
+    // If this function is generic, then we store a reference
+    // to the AST-level generic that defines its parameters
+    // and their constraints.
+    RefPtr<GenericDecl> genericDecl;
 
     // Convenience accessors for working with the 
     // function's type.