Prevent analysis of functions only referenced at comptime

The idea here is that there are two ways we can reference a function at runtime:

* Through a direct call, i.e. where the function is comptime-known
* Through a function pointer

This means we can easily perform a form of rudimentary escape analysis
on functions. If we ever see a `decl_ref` or `ref` of a function, we
have a function pointer, which could "leak" into runtime code, so we
emit the function; but for a plain `decl_val`, there's no need to.

This change means that `comptime { _ = f; }` no longer forces a function
to be emitted, which was used for some things (mainly tests). These use
sites have been replaced with `_ = &f;`, which still triggers analysis
of the function body, since you're taking a pointer to the function.

Resolves: #6256
Resolves: #15353

11 files changed, 21 insertions, 19 deletions

diff --git a/test/cases/compile_errors/closure_get_depends_on_failed_decl.zig b/test/cases/compile_errors/closure_get_depends_on_failed_decl.zig
index ccdbf67713..be451d2fc8 100644
--- a/test/cases/compile_errors/closure_get_depends_on_failed_decl.zig
+++ b/test/cases/compile_errors/closure_get_depends_on_failed_decl.zig
@@ -3,7 +3,7 @@ pub inline fn instanceRequestAdapter() void {}
 pub inline fn requestAdapter(
     comptime callbackArg: fn () callconv(.Inline) void,
 ) void {
-    _ = (struct {
+    _ = &(struct {
         pub fn callback() callconv(.C) void {
             callbackArg();
         }
diff --git a/test/cases/compile_errors/compileLog_of_tagged_enum_doesnt_crash_the_compiler.zig b/test/cases/compile_errors/compileLog_of_tagged_enum_doesnt_crash_the_compiler.zig
index 55676f9230..f7de8129b7 100644
--- a/test/cases/compile_errors/compileLog_of_tagged_enum_doesnt_crash_the_compiler.zig
+++ b/test/cases/compile_errors/compileLog_of_tagged_enum_doesnt_crash_the_compiler.zig
@@ -1,5 +1,5 @@
 const Bar = union(enum(u32)) {
-    X: i32 = 1
+    X: i32 = 1,
 };
 
 fn testCompileLog(x: Bar) void {
@@ -7,7 +7,8 @@ fn testCompileLog(x: Bar) void {
 }
 
 pub export fn entry() void {
-    comptime testCompileLog(Bar{.X = 123});
+    comptime testCompileLog(Bar{ .X = 123 });
+    _ = &testCompileLog;
 }
 
 // error
diff --git a/test/cases/compile_errors/compile_log.zig b/test/cases/compile_errors/compile_log.zig
index e1ea460dc3..444d091017 100644
--- a/test/cases/compile_errors/compile_log.zig
+++ b/test/cases/compile_errors/compile_log.zig
@@ -1,10 +1,11 @@
 export fn foo() void {
-    comptime bar(12, "hi",);
+    comptime bar(12, "hi");
+    _ = &bar;
 }
 fn bar(a: i32, b: []const u8) void {
-    @compileLog("begin",);
+    @compileLog("begin");
     @compileLog("a", a, "b", b);
-    @compileLog("end",);
+    @compileLog("end");
 }
 export fn baz() void {
     const S = struct { a: u32 };
@@ -15,8 +16,8 @@ export fn baz() void {
 // backend=llvm
 // target=native
 //
-// :5:5: error: found compile log statement
-// :11:5: note: also here
+// :6:5: error: found compile log statement
+// :12:5: note: also here
 //
 // Compile Log Output:
 // @as(*const [5:0]u8, "begin")
diff --git a/test/cases/compile_errors/dereference_slice.zig b/test/cases/compile_errors/dereference_slice.zig
index 7dba3b55d8..55d6078b22 100644
--- a/test/cases/compile_errors/dereference_slice.zig
+++ b/test/cases/compile_errors/dereference_slice.zig
@@ -2,7 +2,7 @@ fn entry(x: []i32) i32 {
     return x.*;
 }
 comptime {
-    _ = entry;
+    _ = &entry;
 }
 
 // error
diff --git a/test/cases/compile_errors/extern_function_with_comptime_parameter.zig b/test/cases/compile_errors/extern_function_with_comptime_parameter.zig
index 58f15f7fab..8ade9ca2aa 100644
--- a/test/cases/compile_errors/extern_function_with_comptime_parameter.zig
+++ b/test/cases/compile_errors/extern_function_with_comptime_parameter.zig
@@ -4,9 +4,9 @@ fn f() i32 {
 }
 pub extern fn entry1(b: u32, comptime a: [2]u8, c: i32) void;
 pub extern fn entry2(b: u32, noalias a: anytype, i43) void;
-comptime { _ = f; }
-comptime { _ = entry1; }
-comptime { _ = entry2; }
+comptime { _ = &f; }
+comptime { _ = &entry1; }
+comptime { _ = &entry2; }
 
 // error
 // backend=stage2
diff --git a/test/cases/compile_errors/invalid_address_space_coercion.zig b/test/cases/compile_errors/invalid_address_space_coercion.zig
index 4633b12e0f..baf37cbe37 100644
--- a/test/cases/compile_errors/invalid_address_space_coercion.zig
+++ b/test/cases/compile_errors/invalid_address_space_coercion.zig
@@ -2,7 +2,7 @@ fn entry(a: *addrspace(.gs) i32) *i32 {
     return a;
 }
 pub fn main() void {
-    _ = entry;
+    _ = &entry;
 }
 
 // error
diff --git a/test/cases/compile_errors/invalid_pointer_keeps_address_space_when_taking_address_of_dereference.zig b/test/cases/compile_errors/invalid_pointer_keeps_address_space_when_taking_address_of_dereference.zig
index 4d7b3c627b..c59238d6a7 100644
--- a/test/cases/compile_errors/invalid_pointer_keeps_address_space_when_taking_address_of_dereference.zig
+++ b/test/cases/compile_errors/invalid_pointer_keeps_address_space_when_taking_address_of_dereference.zig
@@ -2,7 +2,7 @@ fn entry(a: *addrspace(.gs) i32) *i32 {
     return &a.*;
 }
 pub fn main() void {
-    _ = entry;
+    _ = &entry;
 }
 
 // error
diff --git a/test/cases/compile_errors/noalias_on_non_pointer_param.zig b/test/cases/compile_errors/noalias_on_non_pointer_param.zig
index 806808820f..65e6e141ce 100644
--- a/test/cases/compile_errors/noalias_on_non_pointer_param.zig
+++ b/test/cases/compile_errors/noalias_on_non_pointer_param.zig
@@ -2,10 +2,10 @@ fn f(noalias x: i32) void { _ = x; }
 export fn entry() void { f(1234); }
 
 fn generic(comptime T: type, noalias _: [*]T, noalias _: [*]const T, _: usize) void  {}
-comptime { _ = generic; }
+comptime { _ = &generic; }
 
 fn slice(noalias _: []u8) void  {}
-comptime { _ = slice; }
+comptime { _ = &slice; }
 
 // error
 // backend=stage2
diff --git a/test/cases/compile_errors/pointer_with_different_address_spaces.zig b/test/cases/compile_errors/pointer_with_different_address_spaces.zig
index 2bbea3d3b6..7a434cfa8e 100644
--- a/test/cases/compile_errors/pointer_with_different_address_spaces.zig
+++ b/test/cases/compile_errors/pointer_with_different_address_spaces.zig
@@ -2,7 +2,7 @@ fn entry(a: *addrspace(.gs) i32) *addrspace(.fs) i32 {
     return a;
 }
 export fn entry2() void {
-    _ = entry;
+    _ = &entry;
 }
 
 // error
diff --git a/test/cases/compile_errors/pointers_with_different_address_spaces.zig b/test/cases/compile_errors/pointers_with_different_address_spaces.zig
index e952da2af5..44b1ef8722 100644
--- a/test/cases/compile_errors/pointers_with_different_address_spaces.zig
+++ b/test/cases/compile_errors/pointers_with_different_address_spaces.zig
@@ -2,7 +2,7 @@ fn entry(a: ?*addrspace(.gs) i32) *i32 {
     return a.?;
 }
 pub fn main() void {
-    _ = entry;
+    _ = &entry;
 }
 
 // error
diff --git a/test/cases/compile_errors/slice_sentinel_mismatch-2.zig b/test/cases/compile_errors/slice_sentinel_mismatch-2.zig
index 3cc5ac4c39..ea34805e32 100644
--- a/test/cases/compile_errors/slice_sentinel_mismatch-2.zig
+++ b/test/cases/compile_errors/slice_sentinel_mismatch-2.zig
@@ -2,7 +2,7 @@ fn foo() [:0]u8 {
     var x: []u8 = undefined;
     return x;
 }
-comptime { _ = foo; }
+comptime { _ = &foo; }
 
 // error
 // backend=stage2