IR: add support for `discard` statement (#261)

- Add definition of `discard` instruction
  - A `discard` is a terminator instruction, just like `returnVoid`

- Lower `DiscardStmt` in AST to a `discard` instruction in the IR

- Emit `discard` instruction as a `discard;` statement when emitting HLSL/GLSL

- Add a test case using the "graphics compute" mode that tests discard. The test writes to one entry in a UAV before doing a conditional (always true at runtime) discard, and then writes to another entry; we expect to see the results of the first write, but not the second.

1 files changed, 5 insertions, 0 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 332125fc6..2b7030897 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -5296,6 +5296,10 @@ emitDeclImpl(decl, nullptr);
             emit(";\n");
             break;
 
+        case kIROp_discard:
+            emit("discard;\n");
+            break;
+
         case kIROp_swizzleSet:
             {
                 auto ii = (IRSwizzleSet*)inst;
@@ -5425,6 +5429,7 @@ emitDeclImpl(decl, nullptr);
 
             case kIROp_ReturnVal:
             case kIROp_ReturnVoid:
+            case kIROp_discard:
                 emitIRInst(ctx, terminator);
                 return;