General purpose teest cases contributed by mw.

src/test/incremental/thinlto/cgu_invalidated_when_import_added.rs

@@ -0,0 +1,62 @@
+// revisions: cfail1 cfail2
+// compile-flags: -O -Zhuman-readable-cgu-names -Cllvm-args=-import-instr-limit=10
+// build-pass
+
+// rust-lang/rust#59535:
+//
+// This is analgous to cgu_invalidated_when_import_removed.rs, but it covers
+// the other direction:
+//
+// We start with a call-graph like `[A] -> [B -> D] [C]` (where the letters are
+// functions and the modules are enclosed in `[]`), and add a new call `D <- C`,
+// yielding the new call-graph: `[A] -> [B -> D] <- [C]`
+//
+// The effect of this is that the compiler previously classfied `D` as internal
+// and the import-set of `[A]` to be just `B`. But after adding the `D <- C` call,
+// `D` is no longer classified as internal, and the import-set of `[A]` becomes
+// both `B` and `D`.
+//
+// We check this case because an early proposed pull request included an
+// assertion that the import-sets monotonically decreased over time, a claim
+// which this test case proves to be false.
+
+fn main() {
+    foo::foo();
+    bar::baz();
+}
+
+mod foo {
+
+    // In cfail1, ThinLTO decides that foo() does not get inlined into main, and
+    // instead bar() gets inlined into foo().
+    // In cfail2, foo() gets inlined into main.
+    pub fn foo(){
+        bar()
+    }
+
+    // This function needs to be big so that it does not get inlined by ThinLTO
+    // but *does* get inlined into foo() when it is declared `internal` in
+    // cfail1 (alone).
+    pub fn bar(){
+        println!("quux1");
+        println!("quux2");
+        println!("quux3");
+        println!("quux4");
+        println!("quux5");
+        println!("quux6");
+        println!("quux7");
+        println!("quux8");
+        println!("quux9");
+    }
+}
+
+mod bar {
+
+    #[inline(never)]
+    pub fn baz() {
+        #[cfg(cfail2)]
+        {
+            crate::foo::bar();
+        }
+    }
+}

src/test/incremental/thinlto/cgu_invalidated_when_import_removed.rs

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+// revisions: cfail1 cfail2
+// compile-flags: -O -Zhuman-readable-cgu-names -Cllvm-args=-import-instr-limit=10
+// build-pass
+
+// rust-lang/rust#59535:
+//
+// Consider a call-graph like `[A] -> [B -> D] <- [C]` (where the letters are
+// functions and the modules are enclosed in `[]`)
+//
+// In our specific instance, the earlier compilations were inlining the call
+// to`B` into `A`; thus `A` ended up with a external reference to the symbol `D`
+// in its object code, to be resolved at subsequent link time. The LTO import
+// information provided by LLVM for those runs reflected that information: it
+// explicitly says during those runs, `B` definition and `D` declaration were
+// imported into `[A]`.
+//
+// The change between incremental builds was that the call `D <- C` was removed.
+//
+// That change, coupled with other decisions within `rustc`, made the compiler
+// decide to make `D` an internal symbol (since it was no longer accessed from
+// other codegen units, this makes sense locally). And then the definition of
+// `D` was inlined into `B` and `D` itself was eliminated entirely.
+//
+// The current LTO import information reported that `B` alone is imported into
+// `[A]` for the *current compilation*. So when the Rust compiler surveyed the
+// dependence graph, it determined that nothing `[A]` imports changed since the
+// last build (and `[A]` itself has not changed either), so it chooses to reuse
+// the object code generated during the previous compilation.
+//
+// But that previous object code has an unresolved reference to `D`, and that
+// causes a link time failure!
+
+fn main() {
+    foo::foo();
+    bar::baz();
+}
+
+mod foo {
+
+    // In cfail1, foo() gets inlined into main.
+    // In cfail2, ThinLTO decides that foo() does not get inlined into main, and
+    // instead bar() gets inlined into foo(). But faulty logic in our incr.
+    // ThinLTO implementation thought that `main()` is unchanged and thus reused
+    // the object file still containing a call to the now non-existant bar().
+    pub fn foo(){
+        bar()
+    }
+
+    // This function needs to be big so that it does not get inlined by ThinLTO
+    // but *does* get inlined into foo() once it is declared `internal` in
+    // cfail2.
+    pub fn bar(){
+        println!("quux1");
+        println!("quux2");
+        println!("quux3");
+        println!("quux4");
+        println!("quux5");
+        println!("quux6");
+        println!("quux7");
+        println!("quux8");
+        println!("quux9");
+    }
+}
+
+mod bar {
+
+    #[inline(never)]
+    pub fn baz() {
+        #[cfg(cfail1)]
+        {
+            crate::foo::bar();
+        }
+    }
+}