Remove StructRet arg attr

It is applied exactly when the return value has an indirect pass mode.
Except for InReg on x86 fastcall, arg attrs are now only used for
optimization purposes and thus are fine to ignore.

Author: bjorn3

compiler/rustc_codegen_llvm/src/abi.rs

@@ -36,7 +36,7 @@ impl ArgAttributeExt for ArgAttribute {
     where
         F: FnMut(llvm::Attribute),
     {
-        for_each_kind!(self, f, NoAlias, NoCapture, NonNull, ReadOnly, StructRet, InReg)
+        for_each_kind!(self, f, NoAlias, NoCapture, NonNull, ReadOnly, InReg)
     }
 }
 
@@ -429,7 +429,8 @@ impl<'tcx> FnAbiLlvmExt<'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             }
             PassMode::Indirect { ref attrs, extra_attrs: _, on_stack } => {
                 assert!(!on_stack);
-                apply(attrs);
+                let i = apply(attrs);
+                llvm::Attribute::StructRet.apply_llfn(llvm::AttributePlace::Argument(i), llfn);
             }
             _ => {}
         }
@@ -484,7 +485,9 @@ impl<'tcx> FnAbiLlvmExt<'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             }
             PassMode::Indirect { ref attrs, extra_attrs: _, on_stack } => {
                 assert!(!on_stack);
-                apply(attrs);
+                let i = apply(attrs);
+                llvm::Attribute::StructRet
+                    .apply_callsite(llvm::AttributePlace::Argument(i), callsite);
             }
             _ => {}
         }

compiler/rustc_middle/src/ty/layout.rs

@@ -2801,10 +2801,6 @@ where
             for arg in &mut self.args {
                 fixup(arg, false);
             }
-            if let PassMode::Indirect { ref mut attrs, extra_attrs: _, on_stack: _ } = self.ret.mode
-            {
-                attrs.set(ArgAttribute::StructRet);
-            }
             return;
         }
 

compiler/rustc_target/src/abi/call/mod.rs

@@ -59,7 +59,6 @@ mod attr_impl {
             const NoCapture = 1 << 2;
             const NonNull   = 1 << 3;
             const ReadOnly  = 1 << 4;
-            const StructRet = 1 << 6;
             const InReg     = 1 << 8;
         }
     }
@@ -619,10 +618,6 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             a => return Err(format!("unrecognized arch \"{}\" in target specification", a)),
         }
 
-        if let PassMode::Indirect { ref mut attrs, extra_attrs: _, on_stack: _ } = self.ret.mode {
-            attrs.set(ArgAttribute::StructRet);
-        }
-
         Ok(())
     }
 }