stage2: implement comptime `@atomicRmw`

 * introduce float_to_int and int_to_float AIR instructionts and
   implement for the LLVM backend and C backend.
 * Sema: implement `zirIntToFloat`.
 * Sema: implement `@atomicRmw` comptime evaluation
   - introduce `storePtrVal` for when one needs to store a Value to a
     pointer which is a Value, and assert it happens at comptime.
 * Value: introduce new functionality:
   - intToFloat
   - numberAddWrap
   - numberSubWrap
   - numberMax
   - numberMin
   - bitwiseAnd
   - bitwiseNand (not implemented yet)
   - bitwiseOr
   - bitwiseXor
 * Sema: hook up `zirBitwise` to the new Value bitwise implementations
 * Type: rename `isFloat` to `isRuntimeFloat` because it returns `false`
   for `comptime_float`.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 5eb4388a9e..6da791cb46 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -917,6 +917,8 @@ fn genBody(o: *Object, body: []const Air.Inst.Index) error{ AnalysisFail, OutOfM
             .atomic_rmw       => try airAtomicRmw(o, inst),
             .atomic_load      => try airAtomicLoad(o, inst),
 
+            .int_to_float, .float_to_int => try airSimpleCast(o, inst),
+
             .atomic_store_unordered => try airAtomicStore(o, inst, toMemoryOrder(.Unordered)),
             .atomic_store_monotonic => try airAtomicStore(o, inst, toMemoryOrder(.Monotonic)),
             .atomic_store_release   => try airAtomicStore(o, inst, toMemoryOrder(.Release)),
@@ -1899,6 +1901,24 @@ fn airArrayToSlice(o: *Object, inst: Air.Inst.Index) !CValue {
     return local;
 }
 
+/// Emits a local variable with the result type and initializes it
+/// with the operand.
+fn airSimpleCast(o: *Object, inst: Air.Inst.Index) !CValue {
+    if (o.liveness.isUnused(inst))
+        return CValue.none;
+
+    const inst_ty = o.air.typeOfIndex(inst);
+    const local = try o.allocLocal(inst_ty, .Const);
+    const ty_op = o.air.instructions.items(.data)[inst].ty_op;
+    const writer = o.writer();
+    const operand = try o.resolveInst(ty_op.operand);
+
+    try writer.writeAll(" = ");
+    try o.writeCValue(writer, operand);
+    try writer.writeAll(";\n");
+    return local;
+}
+
 fn airCmpxchg(o: *Object, inst: Air.Inst.Index, flavor: [*:0]const u8) !CValue {
     const ty_pl = o.air.instructions.items(.data)[inst].ty_pl;
     const extra = o.air.extraData(Air.Cmpxchg, ty_pl.payload).data;