[mlir][emitc] Fix literal translation (#71296)

- Do not emit variables-at-top for literals
- Do not emit an error for a missing name for literals used as call
operands.

Author: aniragil

mlir/lib/Target/Cpp/TranslateToCpp.cpp

@@ -637,6 +637,8 @@ static LogicalResult printOperation(CppEmitter &emitter,
     // regions.
     WalkResult result =
         functionOp.walk<WalkOrder::PreOrder>([&](Operation *op) -> WalkResult {
+          if (isa<emitc::LiteralOp>(op))
+            return WalkResult::skip();
           for (OpResult result : op->getResults()) {
             if (failed(emitter.emitVariableDeclaration(
                     result, /*trailingSemicolon=*/true))) {
@@ -839,7 +841,8 @@ LogicalResult CppEmitter::emitAttribute(Location loc, Attribute attr) {
 
 LogicalResult CppEmitter::emitOperands(Operation &op) {
   auto emitOperandName = [&](Value result) -> LogicalResult {
-    if (!hasValueInScope(result))
+    auto literalDef = dyn_cast_if_present<LiteralOp>(result.getDefiningOp());
+    if (!literalDef && !hasValueInScope(result))
       return op.emitOpError() << "operand value not in scope";
     os << getOrCreateName(result);
     return success();

mlir/test/Target/Cpp/literal.mlir

@@ -10,6 +10,5 @@ func.func @emitc_literal(%arg0: f32) {
 // CPP-DEFAULT: float [[V2:[^ ]*]] = [[V0:[^ ]*]] + M_PI
 
 // CPP-DECLTOP: void emitc_literal(float [[V0:[^ ]*]]) {
-// CPP-DECLTOP: float M_PI;
 // CPP-DECLTOP: float [[V1:[^ ]*]];
 // CPP-DECLTOP: [[V1]] = [[V0:[^ ]*]] + M_PI

mlir/test/Target/Cpp/literal_call_operand.mlir

@@ -1,6 +1,5 @@
 // RUN: mlir-translate -mlir-to-cpp %s | FileCheck %s -check-prefix=CPP-DEFAULT
 // RUN: mlir-translate -mlir-to-cpp -declare-variables-at-top %s | FileCheck %s -check-prefix=CPP-DECLTOP
-// XFAIL: *
 
 func.func @emitc_call_operand() {
   %p0 = emitc.literal "M_PI" : f32
@@ -11,6 +10,5 @@ func.func @emitc_call_operand() {
 // CPP-DEFAULT-NEXT: float v1 = foo(M_PI);
 
 // CPP-DECLTOP: void emitc_call_operand() {
-// CPP-DECLTOP-NEXT: float M_PI;
 // CPP-DECLTOP-NEXT: float v1;
 // CPP-DECLTOP-NEXT: v1 = foo(M_PI);