Fix setting inline hint based on InstanceDef::requires_inline

For instances where `InstanceDef::requires_inline` is true, an attempt
is made to set an inline hint though a call to the `inline` function.
The attempt is ineffective, since all attributes will be usually removed
by the second call.

Fix the issue by applying the attributes only once, with user provided
attributes having a priority when provided.

Author: tmiasko

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -25,7 +25,7 @@ use crate::value::Value;
 
 /// Mark LLVM function to use provided inline heuristic.
 #[inline]
-fn inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr) {
+fn inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr, requires_inline: bool) {
     use self::InlineAttr::*;
     match inline {
         Hint => Attribute::InlineHint.apply_llfn(Function, val),
@@ -35,11 +35,8 @@ fn inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr) {
                 Attribute::NoInline.apply_llfn(Function, val);
             }
         }
-        None => {
-            Attribute::InlineHint.unapply_llfn(Function, val);
-            Attribute::AlwaysInline.unapply_llfn(Function, val);
-            Attribute::NoInline.unapply_llfn(Function, val);
-        }
+        None if requires_inline => Attribute::InlineHint.apply_llfn(Function, val),
+        None => {}
     };
 }
 
@@ -229,12 +226,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
         }
     }
 
-    // FIXME(eddyb) consolidate these two `inline` calls (and avoid overwrites).
-    if instance.def.requires_inline(cx.tcx) {
-        inline(cx, llfn, attributes::InlineAttr::Hint);
-    }
-
-    inline(cx, llfn, codegen_fn_attrs.inline.clone());
+    inline(cx, llfn, codegen_fn_attrs.inline.clone(), instance.def.requires_inline(cx.tcx));
 
     // The `uwtable` attribute according to LLVM is:
     //

src/test/codegen/inline-hint.rs

@@ -0,0 +1,31 @@
+// Checks that closures, constructors, and shims except
+// for a drop glue receive inline hint by default.
+//
+// compile-flags: -Cno-prepopulate-passes -Zsymbol-mangling-version=v0
+#![crate_type = "lib"]
+
+pub fn f() {
+    let a = A;
+    let b = (0i32, 1i32, 2i32, 3i32);
+    let c = || {};
+
+    a(String::new(), String::new());
+    b.clone();
+    c();
+}
+
+struct A(String, String);
+
+// CHECK:      ; core::ptr::drop_in_place::<inline_hint::A>
+// CHECK-NEXT: ; Function Attrs:
+// CHECK-NOT:  inlinehint
+// CHECK-SAME: {{$}}
+
+// CHECK:      ; <(i32, i32, i32, i32) as core::clone::Clone>::clone
+// CHECK-NEXT: ; Function Attrs: inlinehint
+
+// CHECK:      ; inline_hint::f::{closure#0}
+// CHECK-NEXT: ; Function Attrs: inlinehint
+
+// CHECK:      ; inline_hint::A
+// CHECK-NEXT: ; Function Attrs: inlinehint