Arguments are evaluated multiple times when a generic return type turns out to be comptime-only

[mlugg]

Zig Version

0.14.0-dev.2443+3f7b3daaa

Steps to Reproduce and Observed Behavior

test {
    comptime var foo: u32 = 0;
    _ = bar({
        foo += 1;
    });
    @compileLog(foo);
}

fn bar(val: anytype) if (@TypeOf(val) == void) comptime_int else u32 {
    return 123;
}

$ zig test foo.zig
foo.zig:6:5: error: found compile log statement
    @compileLog(foo);
    ^~~~~~~~~~~~~~~~

Compile Log Output:
@as(u32, 2)

Expected Behavior

The logged value should be 1, because the argument expression should only be evaluated once.

This happens because:

• Sema.analyzeCall notices that we are calling a generic function, so calls Sema.instantiateGenericCall
• After evaluating the arguments, instantiateGenericCall notices that the resolved return type is comptime-only, so returns error.ComptimeReturn
• Sema.analyzeCall catches this and performs a comptime call instead
• This code path re-evaluates the arguments

To fix this, the resolved argument values must be cached after they are first analyzed; perhaps by CallArgsInfo itself, or perhaps through some specialized mechanism between analyzeCall and instantiateGenericCall.