llvm_ir_generator: handle no-op coercions.

artiq/compiler/transforms/llvm_ir_generator.py

@@ -848,6 +848,8 @@ class LLVMIRGenerator:
 
     def process_Coerce(self, insn):
         typ, value_typ = insn.type, insn.value().type
+        if typ == value_typ:
+            return self.map(insn.value())
         if builtins.is_int(typ) and builtins.is_float(value_typ):
             return self.llbuilder.fptosi(self.map(insn.value()), self.llty_of_type(typ),
                                          name=insn.name)

artiq/test/lit/codegen/noop_coercion.py

@@ -0,0 +1,4 @@
+# RUN: %python -m artiq.compiler.testbench.llvmgen %s
+
+def f():
+    return float(1.0)