Auto merge of #35409 - eddyb:mir-storage-stmts, r=nikomatsakis

[MIR] Add Storage{Live,Dead} statements to emit llvm.lifetime.{start,end}.

Storage live ranges are tracked for all MIR variables and temporaries with a drop scope.
`StorageLive` is lowered to `llvm.lifetime.start` and `StorageDead` to `llvm.lifetime.end`.

There are some improvements possible here, such as:
* pack multiple storage liveness statements by using the index of first local + `u64` bitset
* enforce that locals are not directly accessed outside their storage live range
* shrink storage live ranges for never-borrowed locals to initialization -> last use
* emit storage liveness statements for *all* temporaries
 * however, the remaining ones are *always* SSA immediates, so they'd be noop in MIR trans
 * could have a flag on the temporary that its storage is irrelevant (a la C's old `register`)
   * would also deny borrows if necessary
    * this seems like an overcompliation and with packing & optimizations it may be pointless

Even in the current state, it helps stage2 `rustc` compile `boiler` without overflowing (see #35408).

A later addition fixes #26764 and closes #27372 by emitting `.section` directives for dylib metadata to avoid them being allocated into memory or read as `.note`. For this PR, those bugs were tripping valgrind.

1 files changed, 54 insertions, 0 deletions

diff --git a/src/test/codegen/lifetime_start_end.rs b/src/test/codegen/lifetime_start_end.rs
new file mode 100644
index 00000000000..cf91e7a8bcb
--- /dev/null
+++ b/src/test/codegen/lifetime_start_end.rs
@@ -0,0 +1,54 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -O -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+#![feature(rustc_attrs)]
+
+// CHECK-LABEL: @test
+#[no_mangle]
+#[rustc_mir] // FIXME #27840 MIR has different codegen.
+pub fn test() {
+    let a = 0;
+    &a; // keep variable in an alloca
+
+// CHECK: [[S_a:%[0-9]+]] = bitcast i32* %a to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_a]])
+
+    {
+        let b = &Some(a);
+        &b; // keep variable in an alloca
+
+// CHECK: [[S_b:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"** %b to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_b]])
+
+// CHECK: [[S_tmp2:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"* %tmp2 to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_tmp2]])
+
+// CHECK: [[E_tmp2:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"* %tmp2 to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_tmp2]])
+
+// CHECK: [[E_b:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"** %b to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_b]])
+    }
+
+    let c = 1;
+    &c; // keep variable in an alloca
+
+// CHECK: [[S_c:%[0-9]+]] = bitcast i32* %c to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_c]])
+
+// CHECK: [[E_c:%[0-9]+]] = bitcast i32* %c to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_c]])
+
+// CHECK: [[E_a:%[0-9]+]] = bitcast i32* %a to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_a]])
+}