IR: support for select and negate (shader-slang#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.

Author: Tim Foley

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;

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");

tests/compute/select-expr.slang

@@ -0,0 +1,18 @@
+//TEST(smoke,compute):COMPARE_COMPUTE:
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+
+// Test IR code generation for the `?:` "select" operator
+
+int test(int input)
+{
+	return input > 1 ? -input : input;
+}
+
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    outputBuffer[dispatchThreadID.x] = test((int) dispatchThreadID.x);
+}

tests/compute/select-expr.slang.expected.txt

@@ -0,0 +1,4 @@
+0
+1
+FFFFFFFE
+FFFFFFFD