Auto merge of #35764 - eddyb:byegone, r=nikomatsakis

Remove the old AST-based backend from rustc_trans.

Starting with Rust 1.13, `--disable-orbit` , `-Z orbit=off` and `#[rustc_no_mir]` have been removed.
Only the new MIR backend is left in the compiler, and only early const_eval uses ASTs from other crates.

Filling drop (previously "zeroing drop"), `#[unsafe_no_drop_flag]` and associated unstable APIs are gone.
Implementing `Drop` doesn't add a flag anymore to the type, all of the dynamic drop is function local.
This is a [breaking-change], please use `Option::None` and/or `mem::forget` if you are unsure about your ability to prevent/control the drop of a value. In the future, `union` will be usable in some such cases.

**NOTE**: DO NOT MERGE before we get the new beta as the stage0, there's some cruft to remove.

All of this will massively simplify any efforts to implement (and as such it blocks) features such as `union`s, safe use of `#[packed]` or new type layout optimizations, not to mention many other experiments.

9 files changed, 30 insertions, 45 deletions

diff --git a/src/test/codegen/adjustments.rs b/src/test/codegen/adjustments.rs
index 20d04939434..40603845da2 100644
--- a/src/test/codegen/adjustments.rs
+++ b/src/test/codegen/adjustments.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 // Hack to get the correct size for the length part in slices
 // CHECK: @helper([[USIZE:i[0-9]+]])
@@ -21,13 +20,12 @@ fn helper(_: usize) {
 
 // CHECK-LABEL: @no_op_slice_adjustment
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn no_op_slice_adjustment(x: &[u8]) -> &[u8] {
     // We used to generate an extra alloca and memcpy for the block's trailing expression value, so
     // check that we copy directly to the return value slot
-// CHECK: [[SRC:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %x to
-// CHECK: [[DST:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %sret_slot to i8*
-// CHECK: call void @llvm.memcpy.{{.*}}(i8* [[DST]], i8* [[SRC]],
+// CHECK: %2 = insertvalue { i8*, [[USIZE]] } undef, i8* %0, 0
+// CHECK: %3 = insertvalue { i8*, [[USIZE]] } %2, [[USIZE]] %1, 1
+// CHECK: ret { i8*, [[USIZE]] } %3
     { x }
 }
 
diff --git a/src/test/codegen/coercions.rs b/src/test/codegen/coercions.rs
index 74c7192259a..c8c9f5b407c 100644
--- a/src/test/codegen/coercions.rs
+++ b/src/test/codegen/coercions.rs
@@ -11,14 +11,12 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 static X: i32 = 5;
 
 // CHECK-LABEL: @raw_ptr_to_raw_ptr_noop
 // CHECK-NOT: alloca
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn raw_ptr_to_raw_ptr_noop() -> *const i32{
     &X as *const i32
 }
@@ -26,7 +24,6 @@ pub fn raw_ptr_to_raw_ptr_noop() -> *const i32{
 // CHECK-LABEL: @reference_to_raw_ptr_noop
 // CHECK-NOT: alloca
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn reference_to_raw_ptr_noop() -> *const i32 {
     &X
 }
diff --git a/src/test/codegen/consts.rs b/src/test/codegen/consts.rs
index ea4c932d435..36a582ca737 100644
--- a/src/test/codegen/consts.rs
+++ b/src/test/codegen/consts.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 // Below, these constants are defined as enum variants that by itself would
 // have a lower alignment than the enum type. Ensure that we mark them
@@ -20,11 +19,12 @@
 // CHECK: @STATIC = {{.*}}, align 4
 
 // This checks the constants from inline_enum_const
-// CHECK: @const{{[0-9]+}} = {{.*}}, align 2
+// CHECK: @ref{{[0-9]+}} = {{.*}}, align 2
 
 // This checks the constants from {low,high}_align_const, they share the same
 // constant, but the alignment differs, so the higher one should be used
-// CHECK: @const{{[0-9]+}} = {{.*}}, align 4
+// CHECK: [[LOW_HIGH:@ref[0-9]+]] = {{.*}}, align 4
+// CHECK: [[LOW_HIGH_REF:@const[0-9]+]] = {{.*}} [[LOW_HIGH]]
 
 #[derive(Copy, Clone)]
 
@@ -40,32 +40,28 @@ pub static STATIC: E<i16, i32> = E::A(0);
 
 // CHECK-LABEL: @static_enum_const
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn static_enum_const() -> E<i16, i32> {
    STATIC
 }
 
 // CHECK-LABEL: @inline_enum_const
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn inline_enum_const() -> E<i8, i16> {
-    E::A(0)
+    *&E::A(0)
 }
 
 // CHECK-LABEL: @low_align_const
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn low_align_const() -> E<i16, [i16; 3]> {
 // Check that low_align_const and high_align_const use the same constant
-// CHECK: call void @llvm.memcpy.{{.*}}(i8* %{{[0-9]+}}, i8* {{.*}} [[LOW_HIGH:@const[0-9]+]]
-    E::A(0)
+// CHECK: load {{.*}} bitcast ({ i16, i16, [4 x i8] }** [[LOW_HIGH_REF]]
+    *&E::A(0)
 }
 
 // CHECK-LABEL: @high_align_const
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn high_align_const() -> E<i16, i32> {
 // Check that low_align_const and high_align_const use the same constant
-// CHECK: call void @llvm.memcpy.{{.*}}(i8* %{{[0-9]}}, i8* {{.*}} [[LOW_HIGH]]
-    E::A(0)
+// CHECK: load {{.*}} bitcast ({ i16, i16, [4 x i8] }** [[LOW_HIGH_REF]]
+    *&E::A(0)
 }
diff --git a/src/test/codegen/drop.rs b/src/test/codegen/drop.rs
index 25f8c130469..a4bd5cf2c15 100644
--- a/src/test/codegen/drop.rs
+++ b/src/test/codegen/drop.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 struct SomeUniqueName;
 
@@ -25,19 +24,20 @@ pub fn possibly_unwinding() {
 
 // CHECK-LABEL: @droppy
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn droppy() {
 // Check that there are exactly 6 drop calls. The cleanups for the unwinding should be reused, so
 // that's one new drop call per call to possibly_unwinding(), and finally 3 drop calls for the
 // regular function exit. We used to have problems with quadratic growths of drop calls in such
 // functions.
-// CHECK: call{{.*}}drop{{.*}}SomeUniqueName
-// CHECK: call{{.*}}drop{{.*}}SomeUniqueName
-// CHECK: call{{.*}}drop{{.*}}SomeUniqueName
+// CHECK-NOT: invoke{{.*}}drop{{.*}}SomeUniqueName
 // CHECK: call{{.*}}drop{{.*}}SomeUniqueName
 // CHECK: call{{.*}}drop{{.*}}SomeUniqueName
 // CHECK: call{{.*}}drop{{.*}}SomeUniqueName
 // CHECK-NOT: call{{.*}}drop{{.*}}SomeUniqueName
+// CHECK: invoke{{.*}}drop{{.*}}SomeUniqueName
+// CHECK: invoke{{.*}}drop{{.*}}SomeUniqueName
+// CHECK: invoke{{.*}}drop{{.*}}SomeUniqueName
+// CHECK-NOT: {{(call|invoke).*}}drop{{.*}}SomeUniqueName
 // The next line checks for the } that ends the function definition
 // CHECK-LABEL: {{^[}]}}
     let _s = SomeUniqueName;
diff --git a/src/test/codegen/loads.rs b/src/test/codegen/loads.rs
index a65a3e1bb66..def5269e07a 100644
--- a/src/test/codegen/loads.rs
+++ b/src/test/codegen/loads.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 pub struct Bytes {
   a: u8,
@@ -22,15 +21,14 @@ pub struct Bytes {
 
 // CHECK-LABEL: @borrow
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn borrow(x: &i32) -> &i32 {
 // CHECK: load {{(i32\*, )?}}i32** %x{{.*}}, !nonnull
+    &x; // keep variable in an alloca
     x
 }
 
 // CHECK-LABEL: @_box
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn _box(x: Box<i32>) -> i32 {
 // CHECK: load {{(i32\*, )?}}i32** %x{{.*}}, !nonnull
     *x
diff --git a/src/test/codegen/mir_zst_stores.rs b/src/test/codegen/mir_zst_stores.rs
index c1acdaf7031..a2cedc853a1 100644
--- a/src/test/codegen/mir_zst_stores.rs
+++ b/src/test/codegen/mir_zst_stores.rs
@@ -10,7 +10,6 @@
 
 // compile-flags: -C no-prepopulate-passes
 
-#![feature(rustc_attrs)]
 #![crate_type = "lib"]
 use std::marker::PhantomData;
 
@@ -19,7 +18,6 @@ struct Zst { phantom: PhantomData<Zst> }
 
 // CHECK-LABEL: @mir
 #[no_mangle]
-#[rustc_mir]
 fn mir(){
     // CHECK-NOT: getelementptr
     // CHECK-NOT: store{{.*}}undef
diff --git a/src/test/codegen/naked-functions.rs b/src/test/codegen/naked-functions.rs
index 199f7f02018..9de74f72005 100644
--- a/src/test/codegen/naked-functions.rs
+++ b/src/test/codegen/naked-functions.rs
@@ -13,7 +13,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(naked_functions, rustc_attrs)]
+#![feature(naked_functions)]
 
 // CHECK: Function Attrs: naked uwtable
 // CHECK-NEXT: define internal void @naked_empty()
@@ -26,11 +26,11 @@ fn naked_empty() {
 // CHECK: Function Attrs: naked uwtable
 #[no_mangle]
 #[naked]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 // CHECK-NEXT: define internal void @naked_with_args(i{{[0-9]+}})
 fn naked_with_args(a: isize) {
     // CHECK: %a = alloca i{{[0-9]+}}
     // CHECK: ret void
+    &a; // keep variable in an alloca
 }
 
 // CHECK: Function Attrs: naked uwtable
@@ -46,10 +46,10 @@ fn naked_with_return() -> isize {
 // CHECK-NEXT: define internal i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+}})
 #[no_mangle]
 #[naked]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 fn naked_with_args_and_return(a: isize) -> isize {
     // CHECK: %a = alloca i{{[0-9]+}}
     // CHECK: ret i{{[0-9]+}} %{{[0-9]+}}
+    &a; // keep variable in an alloca
     a
 }
 
diff --git a/src/test/codegen/refs.rs b/src/test/codegen/refs.rs
index 36c83412e4f..49ed2229fcd 100644
--- a/src/test/codegen/refs.rs
+++ b/src/test/codegen/refs.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 // Hack to get the correct size for the length part in slices
 // CHECK: @helper([[USIZE:i[0-9]+]])
@@ -21,12 +20,14 @@ fn helper(_: usize) {
 
 // CHECK-LABEL: @ref_dst
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn ref_dst(s: &[u8]) {
     // We used to generate an extra alloca and memcpy to ref the dst, so check that we copy
     // directly to the alloca for "x"
-// CHECK: [[SRC:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %s to i8*
-// CHECK: [[DST:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %x to i8*
-// CHECK: call void @llvm.memcpy.{{.*}}(i8* [[DST]], i8* [[SRC]],
+// CHECK: [[X0:%[0-9]+]] = getelementptr {{.*}} { i8*, [[USIZE]] }* %x, i32 0, i32 0
+// CHECK: store i8* %0, i8** [[X0]]
+// CHECK: [[X1:%[0-9]+]] = getelementptr {{.*}} { i8*, [[USIZE]] }* %x, i32 0, i32 1
+// CHECK: store [[USIZE]] %1, [[USIZE]]* [[X1]]
+
     let x = &*s;
+    &x; // keep variable in an alloca
 }
diff --git a/src/test/codegen/stores.rs b/src/test/codegen/stores.rs
index 89bb5d93c74..9141b7245e3 100644
--- a/src/test/codegen/stores.rs
+++ b/src/test/codegen/stores.rs
@@ -11,7 +11,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
-#![feature(rustc_attrs)]
 
 pub struct Bytes {
   a: u8,
@@ -24,12 +23,11 @@ pub struct Bytes {
 // The array is stored as i32, but its alignment is lower, go with 1 byte to avoid target
 // dependent alignment
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn small_array_alignment(x: &mut [i8; 4], y: [i8; 4]) {
-// CHECK: %y = alloca [4 x i8]
+// CHECK: %arg1 = alloca [4 x i8]
 // CHECK: [[TMP:%.+]] = alloca i32
 // CHECK: store i32 %1, i32* [[TMP]]
-// CHECK: [[Y8:%[0-9]+]] = bitcast [4 x i8]* %y to i8*
+// CHECK: [[Y8:%[0-9]+]] = bitcast [4 x i8]* %arg1 to i8*
 // CHECK: [[TMP8:%[0-9]+]] = bitcast i32* [[TMP]] to i8*
 // CHECK: call void @llvm.memcpy.{{.*}}(i8* [[Y8]], i8* [[TMP8]], i{{[0-9]+}} 4, i32 1, i1 false)
     *x = y;
@@ -39,12 +37,11 @@ pub fn small_array_alignment(x: &mut [i8; 4], y: [i8; 4]) {
 // The struct is stored as i32, but its alignment is lower, go with 1 byte to avoid target
 // dependent alignment
 #[no_mangle]
-#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn small_struct_alignment(x: &mut Bytes, y: Bytes) {
-// CHECK: %y = alloca %Bytes
+// CHECK: %arg1 = alloca %Bytes
 // CHECK: [[TMP:%.+]] = alloca i32
 // CHECK: store i32 %1, i32* [[TMP]]
-// CHECK: [[Y8:%[0-9]+]] = bitcast %Bytes* %y to i8*
+// CHECK: [[Y8:%[0-9]+]] = bitcast %Bytes* %arg1 to i8*
 // CHECK: [[TMP8:%[0-9]+]] = bitcast i32* [[TMP]] to i8*
 // CHECK: call void @llvm.memcpy.{{.*}}(i8* [[Y8]], i8* [[TMP8]], i{{[0-9]+}} 4, i32 1, i1 false)
     *x = y;