IR: support for select and negate (#257)

- During IR emit, treat a "select" expression (`?:` operator) like any other `InvokeExpr`, since it will have an `__intrinsic_op` modifier attached to turn it into a `select` instruction.

- During HLSL/GLSL emit from IR, turn a `select` instruction into a `?:` expression

- Also add support for the `neg` instruction during HLSL/GLSL emit

Note that right now we are assuming HLSL semantics for `?:` where it does not short-circuit. Correctly handling the GLSL case would require going back to special-case codegen for `SelectExpr`, but we can cross that bridge when we come to it.

2 files changed, 17 insertions, 5 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index d95946204..b66ff76c9 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -4911,6 +4911,13 @@ emitDeclImpl(decl, nullptr);
             }
             break;
 
+        case kIROp_Neg:
+            {
+                emit("-");
+                emitIROperand(ctx, inst->getArg(0));
+            }
+            break;
+
         case kIROp_Sample:
             emitIROperand(ctx, inst->getArg(0));
             emit(".Sample(");
@@ -5033,6 +5040,16 @@ emitDeclImpl(decl, nullptr);
             }
             break;
 
+        case kIROp_Select:
+            {
+                emitIROperand(ctx, inst->getArg(0));
+                emit(" ? ");
+                emitIROperand(ctx, inst->getArg(1));
+                emit(" : ");
+                emitIROperand(ctx, inst->getArg(2));
+            }
+            break;
+
         default:
             emit("/* unhandled */");
             break;
diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 2672c5698..2c64c539b 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -1497,11 +1497,6 @@ struct ExprLoweringVisitorBase : ExprVisitor<Derived, LoweredValInfo>
         return emitDeclRef(context, expr->declRef);
     }
 
-    LoweredValInfo visitSelectExpr(SelectExpr* /*expr*/)
-    {
-        SLANG_UNIMPLEMENTED_X("codegen for select expression");
-    }
-
     LoweredValInfo visitGenericAppExpr(GenericAppExpr* /*expr*/)
     {
         SLANG_UNIMPLEMENTED_X("generic application expression during code generation");