GVN: Use the borrows only if they are always live

compiler/rustc_middle/src/mir/statement.rs

@@ -374,6 +374,12 @@ impl<'tcx> Place<'tcx> {
         self.projection.iter().any(|elem| elem.is_indirect())
     }
 
+    /// Returns `true` if all projection of this `Place` always refers to the same memory region
+    /// whatever the state of the program.
+    pub fn is_stable_offset(&self) -> bool {
+        self.projection.iter().all(|elem| elem.is_stable_offset())
+    }
+
     /// Returns `true` if this `Place`'s first projection is `Deref`.
     ///
     /// This is useful because for MIR phases `AnalysisPhase::PostCleanup` and later,

compiler/rustc_middle/src/mir/terminator.rs

@@ -695,28 +695,6 @@ impl<'tcx> TerminatorKind<'tcx> {
             _ => None,
         }
     }
-
-    /// Returns true if the terminator can write to memory.
-    pub fn can_write_to_memory(&self) -> bool {
-        match self {
-            TerminatorKind::Goto { .. }
-            | TerminatorKind::SwitchInt { .. }
-            | TerminatorKind::UnwindResume
-            | TerminatorKind::UnwindTerminate(_)
-            | TerminatorKind::Return
-            | TerminatorKind::Assert { .. }
-            | TerminatorKind::CoroutineDrop
-            | TerminatorKind::FalseEdge { .. }
-            | TerminatorKind::FalseUnwind { .. }
-            | TerminatorKind::Unreachable => false,
-            TerminatorKind::Call { .. }
-            | TerminatorKind::Drop { .. }
-            | TerminatorKind::TailCall { .. }
-            // Yield writes to the resume_arg place.
-            | TerminatorKind::Yield { .. }
-            | TerminatorKind::InlineAsm { .. } => true,
-        }
-    }
 }
 
 #[derive(Copy, Clone, Debug)]