Mark inout asm! operands as used in liveness pass

compiler/rustc_passes/src/liveness.rs

@@ -1174,7 +1174,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                             }
                         }
                         hir::InlineAsmOperand::InOut { expr, .. } => {
-                            succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE);
+                            succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE | ACC_USE);
                         }
                         hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
                             if let Some(expr) = out_expr {

src/test/ui/liveness/liveness-asm.rs

@@ -0,0 +1,44 @@
+// Ensure inout asm! operands are marked as used by the liveness pass
+
+// only-x86_64
+// check-pass
+
+#![feature(asm)]
+#![allow(dead_code)]
+#![warn(unused_assignments)]
+#![warn(unused_variables)]
+
+// Test the single inout case
+unsafe fn f1(mut src: *const u8) {
+    asm!("/*{0}*/", inout(reg) src); //~ WARN value assigned to `src` is never read
+}
+
+unsafe fn f2(mut src: *const u8) -> *const u8 {
+    asm!("/*{0}*/", inout(reg) src);
+    src
+}
+
+// Test the split inout case
+unsafe fn f3(mut src: *const u8) {
+    asm!("/*{0}*/", inout(reg) src => src); //~ WARN value assigned to `src` is never read
+}
+
+unsafe fn f4(mut src: *const u8) -> *const u8 {
+    asm!("/*{0}*/", inout(reg) src => src);
+    src
+}
+
+// Tests the use of field projections
+struct S {
+    field: *mut u8,
+}
+
+unsafe fn f5(src: &mut S) {
+    asm!("/*{0}*/", inout(reg) src.field);
+}
+
+unsafe fn f6(src: &mut S) {
+    asm!("/*{0}*/", inout(reg) src.field => src.field);
+}
+
+fn main() {}

src/test/ui/liveness/liveness-asm.stderr

@@ -0,0 +1,23 @@
+warning: value assigned to `src` is never read
+  --> $DIR/liveness-asm.rs:13:32
+   |
+LL |     asm!("/*{0}*/", inout(reg) src);
+   |                                ^^^
+   |
+note: the lint level is defined here
+  --> $DIR/liveness-asm.rs:8:9
+   |
+LL | #![warn(unused_assignments)]
+   |         ^^^^^^^^^^^^^^^^^^
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `src` is never read
+  --> $DIR/liveness-asm.rs:23:39
+   |
+LL |     asm!("/*{0}*/", inout(reg) src => src);
+   |                                       ^^^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: 2 warnings emitted
+