Merge from rustc

Author: The Miri Conjob Bot

tests/fail/function_calls/target_feature.rs

@@ -0,0 +1,11 @@
+//@only-target-x86_64: uses x86 target features
+
+fn main() {
+    assert!(!is_x86_feature_detected!("ssse3"));
+    unsafe {
+        ssse3_fn(); //~ ERROR: calling a function that requires unavailable target features: ssse3
+    }
+}
+
+#[target_feature(enable = "ssse3")]
+unsafe fn ssse3_fn() {}

tests/fail/function_calls/target_feature.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: calling a function that requires unavailable target features: ssse3
+  --> $DIR/target_feature.rs:LL:CC
+   |
+LL |         ssse3_fn();
+   |         ^^^^^^^^^^ calling a function that requires unavailable target features: ssse3
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/target_feature.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+

tests/pass/function_calls/target_feature.rs

@@ -0,0 +1,12 @@
+//@only-target-x86_64: uses x86 target features
+//@compile-flags: -C target-feature=+ssse3
+
+fn main() {
+    assert!(is_x86_feature_detected!("ssse3"));
+    unsafe {
+        ssse3_fn();
+    }
+}
+
+#[target_feature(enable = "ssse3")]
+unsafe fn ssse3_fn() {}