Auto merge of #83084 - nagisa:nagisa/features-native, r=petrochenkov

Adjust `-Ctarget-cpu=native` handling in cg_llvm

When cg_llvm encounters the `-Ctarget-cpu=native` it computes an
explciit set of features that applies to the target in order to
correctly compile code for the host CPU (because e.g. `skylake` alone is
not sufficient to tell if some of the instructions are available or
not).

However there were a couple of issues with how we did this. Firstly, the
order in which features were overriden wasn't quite right – conceptually
you'd expect `-Ctarget-cpu=native` option to override the features that
are implicitly set by the target definition. However due to how other
`-Ctarget-cpu` values are handled we must adopt the following order
of priority:

* Features from -Ctarget-cpu=*; are overriden by
* Features implied by --target; are overriden by
* Features from -Ctarget-feature; are overriden by
* function specific features.

Another problem was in that the function level `target-features`
attribute would overwrite the entire set of the globally enabled
features, rather than just the features the
`#[target_feature(enable/disable)]` specified. With something like
`-Ctarget-cpu=native` we'd end up in a situation wherein a function
without `#[target_feature(enable)]` annotation would have a broader
set of features compared to a function with one such attribute. This
turned out to be a cause of heavy run-time regressions in some code
using these function-level attributes in conjunction with
`-Ctarget-cpu=native`, for example.

With this PR rustc is more careful about specifying the entire set of
features for functions that use `#[target_feature(enable/disable)]` or
`#[instruction_set]` attributes.

Sadly testing the original reproducer for this behaviour is quite
impossible – we cannot rely on `-Ctarget-cpu=native` to be anything in
particular on developer or CI machines.

cc https://github.com/rust-lang/rust/issues/83027 `@BurntSushi`

3 files changed, 47 insertions, 18 deletions

diff --git a/src/test/codegen/target-feature-multiple.rs b/src/test/codegen/target-feature-multiple.rs
deleted file mode 100644
index f71a9c3c582..00000000000
--- a/src/test/codegen/target-feature-multiple.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-// only-x86_64
-// compile-flags: -C target-feature=+sse2,-avx,+avx2 -C target-feature=+avx,-avx2
-
-#![crate_type = "lib"]
-
-#[no_mangle]
-pub fn foo() {
-    // CHECK: attributes #0 = { {{.*}}"target-features"="+sse2,-avx,+avx2,+avx,-avx2"{{.*}} }
-}
diff --git a/src/test/codegen/target-feature-on-functions.rs b/src/test/codegen/target-feature-on-functions.rs
deleted file mode 100644
index d4d39d08b1e..00000000000
--- a/src/test/codegen/target-feature-on-functions.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-// only-x86_64
-// compile-flags: -C target-feature=+avx
-
-#![crate_type = "lib"]
-
-#[no_mangle]
-pub fn foo() {
-    // CHECK: attributes #0 = { {{.*}}"target-features"="+avx"{{.*}} }
-}
diff --git a/src/test/codegen/target-feature-overrides.rs b/src/test/codegen/target-feature-overrides.rs
new file mode 100644
index 00000000000..2c19cfd8c22
--- /dev/null
+++ b/src/test/codegen/target-feature-overrides.rs
@@ -0,0 +1,47 @@
+// revisions: COMPAT INCOMPAT
+// needs-llvm-components: x86
+// compile-flags: --target=x86_64-unknown-linux-gnu -Copt-level=3
+// [COMPAT] compile-flags: -Ctarget-feature=+avx2,+avx
+// [INCOMPAT] compile-flags: -Ctarget-feature=-avx2,-avx
+
+// See also src/test/assembly/target-feature-multiple.rs
+#![feature(no_core, lang_items)]
+#![crate_type = "lib"]
+#![no_core]
+
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+extern "C" {
+    fn peach() -> u32;
+}
+
+#[inline]
+#[target_feature(enable = "avx")]
+#[no_mangle]
+pub unsafe fn apple() -> u32 {
+// CHECK-LABEL: @apple()
+// CHECK-SAME: [[APPLEATTRS:#[0-9]+]] {
+// CHECK: {{.*}}call{{.*}}@peach
+    peach()
+}
+
+// target features same as global (not reflected or overriden in IR)
+#[no_mangle]
+pub unsafe fn banana() -> u32 {
+// CHECK-LABEL: @banana()
+// CHECK-SAME: [[BANANAATTRS:#[0-9]+]] {
+// COMPAT: {{.*}}call{{.*}}@peach
+// INCOMPAT: {{.*}}call{{.*}}@apple
+    apple() // Compatible for inline in COMPAT revision and can't be inlined in INCOMPAT
+}
+
+// CHECK: attributes [[APPLEATTRS]]
+// COMPAT-SAME: "target-features"="+avx2,+avx,+avx"
+// INCOMPAT-SAME: "target-features"="-avx2,-avx,+avx"
+// CHECK: attributes [[BANANAATTRS]]
+// CHECK-NOT: target-features
+// CHECK-SAME: }