Auto merge of #45575 - michaelwoerister:tweak-inline-trans-items, r=nikomatsakis

Only instantiate inline- and const-fns if they are referenced (again).

It seems that we have regressed on not translating `#[inline]` functions unless they are actually used. This should bring back this optimization. I also added a regression test this time so it doesn't happen again accidentally.

Fixes #40392.

r? @alexcrichton

UPDATE & PSA
---------------------
This patch **makes translation very lazy** -- in general this is a good thing (we don't want the compiler to do unnecessary work) but it has two consequences:
1. Some error messages are only generated when an item is actually translated. Consequently, this patch will lead to more cases where the compiler will only start emitting errors when the erroneous function is actually used. This has always been true to some extend (e.g. when passing generic values to an intrinsic) but since this is something user-facing it's worth mentioning.
2. When writing tests, one has to make sure that the functions in question are actually generated. In other words, it must not be dead code. This can usually  be achieved by either
    1. making sure the function is exported from the resulting binary or
    2. by making sure the function is called from something that is exported (or `main()`).

Note that it depends on the crate type what functions are exported:
   1. For rlibs and dylibs everything that is reachable from the outside is exported.
   2. For executables, cdylibs, and staticlibs, items are only exported if they are additionally `#[no_mangle]` or have an `#[export_name]`.

The commits in this PR contain many examples of how tests can be updated to comply to the new requirements.

1 files changed, 7 insertions, 7 deletions

diff --git a/src/test/codegen/function-arguments.rs b/src/test/codegen/function-arguments.rs
index d4c7fe9e80a..29e2840c881 100644
--- a/src/test/codegen/function-arguments.rs
+++ b/src/test/codegen/function-arguments.rs
@@ -93,20 +93,20 @@ pub fn struct_return() -> S {
 // Hack to get the correct size for the length part in slices
 // CHECK: @helper([[USIZE:i[0-9]+]] %arg0)
 #[no_mangle]
-fn helper(_: usize) {
+pub fn helper(_: usize) {
 }
 
 // CHECK: @slice(i8* noalias nonnull readonly %arg0.ptr, [[USIZE]] %arg0.meta)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
-fn slice(_: &[u8]) {
+pub fn slice(_: &[u8]) {
 }
 
 // CHECK: @mutable_slice(i8* nonnull %arg0.ptr, [[USIZE]] %arg0.meta)
 // FIXME #25759 This should also have `nocapture`
 // ... there's this LLVM bug that forces us to not use noalias, see #29485
 #[no_mangle]
-fn mutable_slice(_: &mut [u8]) {
+pub fn mutable_slice(_: &mut [u8]) {
 }
 
 // CHECK: @unsafe_slice(%UnsafeInner* nonnull %arg0.ptr, [[USIZE]] %arg0.meta)
@@ -118,23 +118,23 @@ pub fn unsafe_slice(_: &[UnsafeInner]) {
 // CHECK: @str(i8* noalias nonnull readonly %arg0.ptr, [[USIZE]] %arg0.meta)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
-fn str(_: &[u8]) {
+pub fn str(_: &[u8]) {
 }
 
 // CHECK: @trait_borrow({}* nonnull, {}* noalias nonnull readonly)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
-fn trait_borrow(_: &Drop) {
+pub fn trait_borrow(_: &Drop) {
 }
 
 // CHECK: @trait_box({}* noalias nonnull, {}* noalias nonnull readonly)
 #[no_mangle]
-fn trait_box(_: Box<Drop>) {
+pub fn trait_box(_: Box<Drop>) {
 }
 
 // CHECK: { i16*, [[USIZE]] } @return_slice(i16* noalias nonnull readonly %x.ptr, [[USIZE]] %x.meta)
 #[no_mangle]
-fn return_slice(x: &[u16]) -> &[u16] {
+pub fn return_slice(x: &[u16]) -> &[u16] {
   x
 }