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, 12 insertions, 0 deletions

diff --git a/source/slang/ir.cpp b/source/slang/ir.cpp
index b1af6521c..8fbe20aa6 100644
--- a/source/slang/ir.cpp
+++ b/source/slang/ir.cpp
@@ -166,6 +166,7 @@ namespace Slang
         case kIROp_if:
         case kIROp_ifElse:
         case kIROp_loopTest:
+        case kIROp_discard:
             return true;
         }
     }
@@ -1150,6 +1151,17 @@ namespace Slang
         return inst;
     }
 
+    IRInst* IRBuilder::emitDiscard()
+    {
+        auto inst = createInst<IRDiscard>(
+            this,
+            kIROp_discard,
+            nullptr);
+        addInst(inst);
+        return inst;
+    }
+
+
     IRInst* IRBuilder::emitBranch(
         IRBlock*    pBlock)
     {