Enable emission of alignment attrs for pointer params

Instead disable creation of assumptions during inlining using an
LLVM opt flag.

The -Z arg-align-attributes option which previously controlled this
behavior is removed.

src/librustc/session/config.rs

@@ -1271,8 +1271,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "set the MIR optimization level (0-3, default: 1)"),
     mutable_noalias: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes on LLVM >= 6)"),
-    arg_align_attributes: bool = (false, parse_bool, [TRACKED],
-        "emit align metadata for reference arguments"),
     dump_mir: Option<String> = (None, parse_opt_string, [UNTRACKED],
         "dump MIR state to file.
         `val` is used to select which passes and functions to dump. For example:

src/librustc_codegen_llvm/abi.rs

@@ -489,12 +489,6 @@ impl<'tcx> FnTypeExt<'tcx> for FnType<'tcx, Ty<'tcx>> {
                     attrs.pointee_size = pointee.size;
                     attrs.pointee_align = Some(pointee.align);
 
-                    // HACK(eddyb) LLVM inserts `llvm.assume` calls when inlining functions
-                    // with align attributes, and those calls later block optimizations.
-                    if !is_return && !cx.tcx.sess.opts.debugging_opts.arg_align_attributes {
-                        attrs.pointee_align = None;
-                    }
-
                     // `Box` pointer parameters never alias because ownership is transferred
                     // `&mut` pointer parameters never alias other parameters,
                     // or mutable global data

src/librustc_codegen_llvm/llvm_util.rs

@@ -74,6 +74,10 @@ unsafe fn configure_llvm(sess: &Session) {
             add("-mergefunc-use-aliases");
         }
 
+        // HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
+        // during inlining. Unfortunately these may block other optimizations.
+        add("-preserve-alignment-assumptions-during-inlining=false");
+
         for arg in &sess.opts.cg.llvm_args {
             add(&(*arg));
         }

src/test/codegen/function-arguments.rs

@@ -28,37 +28,37 @@ pub fn boolean(x: bool) -> bool {
   x
 }
 
-// CHECK: @readonly_borrow(i32* noalias readonly dereferenceable(4) %arg0)
+// CHECK: @readonly_borrow(i32* noalias readonly align 4 dereferenceable(4) %arg0)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn readonly_borrow(_: &i32) {
 }
 
-// CHECK: @static_borrow(i32* noalias readonly dereferenceable(4) %arg0)
+// CHECK: @static_borrow(i32* noalias readonly align 4 dereferenceable(4) %arg0)
 // static borrow may be captured
 #[no_mangle]
 pub fn static_borrow(_: &'static i32) {
 }
 
-// CHECK: @named_borrow(i32* noalias readonly dereferenceable(4) %arg0)
+// CHECK: @named_borrow(i32* noalias readonly align 4 dereferenceable(4) %arg0)
 // borrow with named lifetime may be captured
 #[no_mangle]
 pub fn named_borrow<'r>(_: &'r i32) {
 }
 
-// CHECK: @unsafe_borrow(i16* dereferenceable(2) %arg0)
+// CHECK: @unsafe_borrow(i16* align 2 dereferenceable(2) %arg0)
 // unsafe interior means this isn't actually readonly and there may be aliases ...
 #[no_mangle]
 pub fn unsafe_borrow(_: &UnsafeInner) {
 }
 
-// CHECK: @mutable_unsafe_borrow(i16* dereferenceable(2) %arg0)
+// CHECK: @mutable_unsafe_borrow(i16* align 2 dereferenceable(2) %arg0)
 // ... unless this is a mutable borrow, those never alias
 #[no_mangle]
 pub fn mutable_unsafe_borrow(_: &mut UnsafeInner) {
 }
 
-// CHECK: @mutable_borrow(i32* dereferenceable(4) %arg0)
+// CHECK: @mutable_borrow(i32* align 4 dereferenceable(4) %arg0)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn mutable_borrow(_: &mut i32) {
@@ -69,13 +69,13 @@ pub fn mutable_borrow(_: &mut i32) {
 pub fn indirect_struct(_: S) {
 }
 
-// CHECK: @borrowed_struct(%S* noalias readonly dereferenceable(32) %arg0)
+// CHECK: @borrowed_struct(%S* noalias readonly align 4 dereferenceable(32) %arg0)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn borrowed_struct(_: &S) {
 }
 
-// CHECK: noalias align 4 dereferenceable(4) i32* @_box(i32* noalias dereferenceable(4) %x)
+// CHECK: noalias align 4 dereferenceable(4) i32* @_box(i32* noalias align 4 dereferenceable(4) %x)
 #[no_mangle]
 pub fn _box(x: Box<i32>) -> Box<i32> {
   x
@@ -95,48 +95,48 @@ pub fn struct_return() -> S {
 pub fn helper(_: usize) {
 }
 
-// CHECK: @slice([0 x i8]* noalias nonnull readonly %arg0.0, [[USIZE]] %arg0.1)
+// CHECK: @slice([0 x i8]* noalias nonnull readonly align 1 %arg0.0, [[USIZE]] %arg0.1)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn slice(_: &[u8]) {
 }
 
-// CHECK: @mutable_slice([0 x i8]* nonnull %arg0.0, [[USIZE]] %arg0.1)
+// CHECK: @mutable_slice([0 x i8]* nonnull align 1 %arg0.0, [[USIZE]] %arg0.1)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn mutable_slice(_: &mut [u8]) {
 }
 
-// CHECK: @unsafe_slice([0 x i16]* nonnull %arg0.0, [[USIZE]] %arg0.1)
+// CHECK: @unsafe_slice([0 x i16]* nonnull align 2 %arg0.0, [[USIZE]] %arg0.1)
 // unsafe interior means this isn't actually readonly and there may be aliases ...
 #[no_mangle]
 pub fn unsafe_slice(_: &[UnsafeInner]) {
 }
 
-// CHECK: @str([0 x i8]* noalias nonnull readonly %arg0.0, [[USIZE]] %arg0.1)
+// CHECK: @str([0 x i8]* noalias nonnull readonly align 1 %arg0.0, [[USIZE]] %arg0.1)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn str(_: &[u8]) {
 }
 
-// CHECK: @trait_borrow({}* nonnull %arg0.0, [3 x [[USIZE]]]* noalias readonly dereferenceable({{.*}}) %arg0.1)
+// CHECK: @trait_borrow({}* nonnull align 1 %arg0.0, [3 x [[USIZE]]]* noalias readonly align {{.*}} dereferenceable({{.*}}) %arg0.1)
 // FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn trait_borrow(_: &Drop) {
 }
 
-// CHECK: @trait_box({}* noalias nonnull, [3 x [[USIZE]]]* noalias readonly dereferenceable({{.*}}))
+// CHECK: @trait_box({}* noalias nonnull align 1, [3 x [[USIZE]]]* noalias readonly align {{.*}} dereferenceable({{.*}}))
 #[no_mangle]
 pub fn trait_box(_: Box<Drop>) {
 }
 
-// CHECK: { i8*, i8* } @trait_option(i8* noalias %x.0, i8* %x.1)
+// CHECK: { i8*, i8* } @trait_option(i8* noalias align 1 %x.0, i8* %x.1)
 #[no_mangle]
 pub fn trait_option(x: Option<Box<Drop>>) -> Option<Box<Drop>> {
   x
 }
 
-// CHECK: { [0 x i16]*, [[USIZE]] } @return_slice([0 x i16]* noalias nonnull readonly %x.0, [[USIZE]] %x.1)
+// CHECK: { [0 x i16]*, [[USIZE]] } @return_slice([0 x i16]* noalias nonnull readonly align 2 %x.0, [[USIZE]] %x.1)
 #[no_mangle]
 pub fn return_slice(x: &[u16]) -> &[u16] {
   x