Auto merge of #26411 - dotdash:fat_in_registers, r=aatch

This has a number of advantages compared to creating a copy in memory
and passing a pointer. The obvious one is that we don't have to put the
data into memory but can keep it in registers. Since we're currently
passing a pointer anyway (instead of using e.g. a known offset on the
stack, which is what the `byval` attribute would achieve), we only use a
single additional register for each fat pointer, but save at least two
pointers worth of stack in exchange (sometimes more because more than
one copy gets eliminated). On archs that pass arguments on the stack, we
save a pointer worth of stack even without considering the omitted
copies.

Additionally, LLVM can optimize the code a lot better, to a large degree
due to the fact that lots of copies are gone or can be optimized away.
Additionally, we can now emit attributes like nonnull on the data and/or
vtable pointers contained in the fat pointer, potentially allowing for
even more optimizations.

This results in LLVM passes being about 3-7% faster (depending on the
crate), and the resulting code is also a few percent smaller, for
example:

|text|data|filename|
|----|----|--------|
|5671479|3941461|before/librustc-d8ace771.so|
|5447663|3905745|after/librustc-d8ace771.so|
| | | |
|1944425|2394024|before/libstd-d8ace771.so|
|1896769|2387610|after/libstd-d8ace771.so|

I had to remove a call in the backtrace-debuginfo test, because LLVM can
now merge the tails of some blocks when optimizations are turned on,
which can't correctly preserve line info.

Fixes #22924

Cc #22891 (at least for fat pointers the code is good now)

Author: bors

src/librustc_llvm/lib.rs

@@ -2252,6 +2252,18 @@ pub fn get_param(llfn: ValueRef, index: c_uint) -> ValueRef {
     }
 }
 
+pub fn get_params(llfn: ValueRef) -> Vec<ValueRef> {
+    unsafe {
+        let num_params = LLVMCountParams(llfn);
+        let mut params = Vec::with_capacity(num_params as usize);
+        for idx in 0..num_params {
+            params.push(LLVMGetParam(llfn, idx));
+        }
+
+        params
+    }
+}
+
 #[allow(missing_copy_implementations)]
 pub enum RustString_opaque {}
 pub type RustStringRef = *mut RustString_opaque;

src/librustc_trans/trans/_match.rs

@@ -828,19 +828,11 @@ fn compare_values<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
                            None,
                            &format!("comparison of `{}`", rhs_t),
                            StrEqFnLangItem);
-        let t = ty::mk_str_slice(cx.tcx(), cx.tcx().mk_region(ty::ReStatic), ast::MutImmutable);
-        // The comparison function gets the slices by value, so we have to make copies here. Even
-        // if the function doesn't write through the pointer, things like lifetime intrinsics
-        // require that we do this properly
-        let lhs_arg = alloc_ty(cx, t, "lhs");
-        let rhs_arg = alloc_ty(cx, t, "rhs");
-        memcpy_ty(cx, lhs_arg, lhs, t);
-        memcpy_ty(cx, rhs_arg, rhs, t);
-        let res = callee::trans_lang_call(cx, did, &[lhs_arg, rhs_arg], None, debug_loc);
-        call_lifetime_end(res.bcx, lhs_arg);
-        call_lifetime_end(res.bcx, rhs_arg);
-
-        res
+        let lhs_data = Load(cx, expr::get_dataptr(cx, lhs));
+        let lhs_len = Load(cx, expr::get_len(cx, lhs));
+        let rhs_data = Load(cx, expr::get_dataptr(cx, rhs));
+        let rhs_len = Load(cx, expr::get_len(cx, rhs));
+        callee::trans_lang_call(cx, did, &[lhs_data, lhs_len, rhs_data, rhs_len], None, debug_loc)
     }
 
     let _icx = push_ctxt("compare_values");

src/librustc_trans/trans/asm.rs

@@ -45,32 +45,31 @@ pub fn trans_inline_asm<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, ia: &ast::InlineAsm)
         output_types.push(type_of::type_of(bcx.ccx(), out_datum.ty));
         let val = out_datum.val;
         if is_rw {
-            ext_inputs.push(unpack_result!(bcx, {
-                callee::trans_arg_datum(bcx,
-                                       expr_ty(bcx, &**out),
-                                       out_datum,
-                                       cleanup::CustomScope(temp_scope),
-                                       callee::DontAutorefArg)
-            }));
+            bcx = callee::trans_arg_datum(bcx,
+                                          expr_ty(bcx, &**out),
+                                          out_datum,
+                                          cleanup::CustomScope(temp_scope),
+                                          callee::DontAutorefArg,
+                                          &mut ext_inputs);
             ext_constraints.push(i.to_string());
         }
         val
 
     }).collect::<Vec<_>>();
 
     // Now the input operands
-    let mut inputs = ia.inputs.iter().map(|&(ref c, ref input)| {
+    let mut inputs = Vec::new();
+    for &(ref c, ref input) in &ia.inputs {
         constraints.push((*c).clone());
 
         let in_datum = unpack_datum!(bcx, expr::trans(bcx, &**input));
-        unpack_result!(bcx, {
-            callee::trans_arg_datum(bcx,
+        bcx = callee::trans_arg_datum(bcx,
                                     expr_ty(bcx, &**input),
                                     in_datum,
                                     cleanup::CustomScope(temp_scope),
-                                    callee::DontAutorefArg)
-        })
-    }).collect::<Vec<_>>();
+                                    callee::DontAutorefArg,
+                                    &mut inputs);
+    }
     inputs.push_all(&ext_inputs[..]);
 
     // no failure occurred preparing operands, no need to cleanup

src/librustc_trans/trans/attributes.rs

@@ -188,7 +188,7 @@ pub fn from_fn_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_type: ty::Ty<'tcx
     };
 
     // Index 0 is the return value of the llvm func, so we start at 1
-    let mut first_arg_offset = 1;
+    let mut idx = 1;
     if let ty::FnConverging(ret_ty) = ret_ty {
         // A function pointer is called without the declaration
         // available, so we have to apply any attributes with ABI
@@ -206,7 +206,7 @@ pub fn from_fn_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_type: ty::Ty<'tcx
                  .arg(1, llvm::DereferenceableAttribute(llret_sz));
 
             // Add one more since there's an outptr
-            first_arg_offset += 1;
+            idx += 1;
         } else {
             // The `noalias` attribute on the return value is useful to a
             // function ptr caller.
@@ -236,10 +236,9 @@ pub fn from_fn_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_type: ty::Ty<'tcx
         }
     }
 
-    for (idx, &t) in input_tys.iter().enumerate().map(|(i, v)| (i + first_arg_offset, v)) {
+    for &t in input_tys.iter() {
         match t.sty {
-            // this needs to be first to prevent fat pointers from falling through
-            _ if !common::type_is_immediate(ccx, t) => {
+            _ if type_of::arg_is_indirect(ccx, t) => {
                 let llarg_sz = machine::llsize_of_real(ccx, type_of::type_of(ccx, t));
 
                 // For non-immediate arguments the callee gets its own copy of
@@ -256,49 +255,63 @@ pub fn from_fn_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_type: ty::Ty<'tcx
 
             // `Box` pointer parameters never alias because ownership is transferred
             ty::TyBox(inner) => {
-                let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, inner));
-
-                attrs.arg(idx, llvm::Attribute::NoAlias)
-                     .arg(idx, llvm::DereferenceableAttribute(llsz));
+                attrs.arg(idx, llvm::Attribute::NoAlias);
+
+                if common::type_is_sized(ccx.tcx(), inner) {
+                    let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, inner));
+                    attrs.arg(idx, llvm::DereferenceableAttribute(llsz));
+                } else {
+                    attrs.arg(idx, llvm::NonNullAttribute);
+                    if ty::type_is_trait(inner) {
+                        attrs.arg(idx + 1, llvm::NonNullAttribute);
+                    }
+                }
             }
 
-            // `&mut` pointer parameters never alias other parameters, or mutable global data
-            //
-            // `&T` where `T` contains no `UnsafeCell<U>` is immutable, and can be marked as both
-            // `readonly` and `noalias`, as LLVM's definition of `noalias` is based solely on
-            // memory dependencies rather than pointer equality
-            ty::TyRef(b, mt) if mt.mutbl == ast::MutMutable ||
-                                  !ty::type_contents(ccx.tcx(), mt.ty).interior_unsafe() => {
+            ty::TyRef(b, mt) => {
+                // `&mut` pointer parameters never alias other parameters, or mutable global data
+                //
+                // `&T` where `T` contains no `UnsafeCell<U>` is immutable, and can be marked as
+                // both `readonly` and `noalias`, as LLVM's definition of `noalias` is based solely
+                // on memory dependencies rather than pointer equality
+                let interior_unsafe = ty::type_contents(ccx.tcx(), mt.ty).interior_unsafe();
 
-                let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, mt.ty));
-                attrs.arg(idx, llvm::Attribute::NoAlias)
-                     .arg(idx, llvm::DereferenceableAttribute(llsz));
+                if mt.mutbl == ast::MutMutable || !interior_unsafe {
+                    attrs.arg(idx, llvm::Attribute::NoAlias);
+                }
 
-                if mt.mutbl == ast::MutImmutable {
+                if mt.mutbl == ast::MutImmutable && !interior_unsafe {
                     attrs.arg(idx, llvm::Attribute::ReadOnly);
                 }
 
+                // & pointer parameters are also never null and for sized types we also know
+                // exactly how many bytes we can dereference
+                if common::type_is_sized(ccx.tcx(), mt.ty) {
+                    let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, mt.ty));
+                    attrs.arg(idx, llvm::DereferenceableAttribute(llsz));
+                } else {
+                    attrs.arg(idx, llvm::NonNullAttribute);
+                    if ty::type_is_trait(mt.ty) {
+                        attrs.arg(idx + 1, llvm::NonNullAttribute);
+                    }
+                }
+
+                // When a reference in an argument has no named lifetime, it's
+                // impossible for that reference to escape this function
+                // (returned or stored beyond the call by a closure).
                 if let ReLateBound(_, BrAnon(_)) = *b {
                     attrs.arg(idx, llvm::Attribute::NoCapture);
                 }
             }
 
-            // When a reference in an argument has no named lifetime, it's impossible for that
-            // reference to escape this function (returned or stored beyond the call by a closure).
-            ty::TyRef(&ReLateBound(_, BrAnon(_)), mt) => {
-                let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, mt.ty));
-                attrs.arg(idx, llvm::Attribute::NoCapture)
-                     .arg(idx, llvm::DereferenceableAttribute(llsz));
-            }
-
-            // & pointer parameters are also never null and we know exactly how
-            // many bytes we can dereference
-            ty::TyRef(_, mt) => {
-                let llsz = machine::llsize_of_real(ccx, type_of::type_of(ccx, mt.ty));
-                attrs.arg(idx, llvm::DereferenceableAttribute(llsz));
-            }
             _ => ()
         }
+
+        if common::type_is_fat_ptr(ccx.tcx(), t) {
+            idx += 2;
+        } else {
+            idx += 1;
+        }
     }
 
     attrs

src/librustc_trans/trans/base.rs

@@ -1297,16 +1297,28 @@ pub type RvalueDatum<'tcx> = datum::Datum<'tcx, datum::Rvalue>;
 // create_datums_for_fn_args: creates rvalue datums for each of the
 // incoming function arguments. These will later be stored into
 // appropriate lvalue datums.
-pub fn create_datums_for_fn_args<'a, 'tcx>(fcx: &FunctionContext<'a, 'tcx>,
+pub fn create_datums_for_fn_args<'a, 'tcx>(bcx: Block<'a, 'tcx>,
                                            arg_tys: &[Ty<'tcx>])
                                            -> Vec<RvalueDatum<'tcx>> {
     let _icx = push_ctxt("create_datums_for_fn_args");
+    let fcx = bcx.fcx;
 
     // Return an array wrapping the ValueRefs that we get from `get_param` for
     // each argument into datums.
-    arg_tys.iter().enumerate().map(|(i, &arg_ty)| {
-        let llarg = get_param(fcx.llfn, fcx.arg_pos(i) as c_uint);
-        datum::Datum::new(llarg, arg_ty, arg_kind(fcx, arg_ty))
+    let mut i = fcx.arg_offset() as c_uint;
+    arg_tys.iter().map(|&arg_ty| {
+        if common::type_is_fat_ptr(bcx.tcx(), arg_ty) {
+            let llty = type_of::type_of(bcx.ccx(), arg_ty);
+            let data = get_param(fcx.llfn, i);
+            let extra = get_param(fcx.llfn, i + 1);
+            let fat_ptr = expr::make_fat_ptr(bcx, llty, data, extra);
+            i += 2;
+            datum::Datum::new(fat_ptr, arg_ty, datum::Rvalue { mode: datum::ByValue })
+        } else {
+            let llarg = get_param(fcx.llfn, i);
+            i += 1;
+            datum::Datum::new(llarg, arg_ty, arg_kind(fcx, arg_ty))
+        }
     }).collect()
 }
 
@@ -1321,12 +1333,23 @@ fn create_datums_for_fn_args_under_call_abi<'blk, 'tcx>(
         arg_tys: &[Ty<'tcx>])
         -> Vec<RvalueDatum<'tcx>> {
     let mut result = Vec::new();
+    let mut idx = bcx.fcx.arg_offset() as c_uint;
     for (i, &arg_ty) in arg_tys.iter().enumerate() {
         if i < arg_tys.len() - 1 {
             // Regular argument.
-            let llarg = get_param(bcx.fcx.llfn, bcx.fcx.arg_pos(i) as c_uint);
-            result.push(datum::Datum::new(llarg, arg_ty, arg_kind(bcx.fcx,
-                                                                  arg_ty)));
+            result.push(if common::type_is_fat_ptr(bcx.tcx(), arg_ty) {
+                let llty = type_of::type_of(bcx.ccx(), arg_ty);
+                let data = get_param(bcx.fcx.llfn, idx);
+                let extra = get_param(bcx.fcx.llfn, idx + 1);
+                idx += 2;
+                let fat_ptr = expr::make_fat_ptr(bcx, llty, data, extra);
+                datum::Datum::new(fat_ptr, arg_ty, datum::Rvalue { mode: datum::ByValue })
+            } else {
+                let val = get_param(bcx.fcx.llfn, idx);
+                idx += 1;
+                datum::Datum::new(val, arg_ty, arg_kind(bcx.fcx, arg_ty))
+            });
+
             continue
         }
 
@@ -1346,15 +1369,21 @@ fn create_datums_for_fn_args_under_call_abi<'blk, 'tcx>(
                                                                llval| {
                         for (j, &tupled_arg_ty) in
                                     tupled_arg_tys.iter().enumerate() {
-                            let llarg =
-                                get_param(bcx.fcx.llfn,
-                                          bcx.fcx.arg_pos(i + j) as c_uint);
                             let lldest = GEPi(bcx, llval, &[0, j]);
-                            let datum = datum::Datum::new(
-                                llarg,
-                                tupled_arg_ty,
-                                arg_kind(bcx.fcx, tupled_arg_ty));
-                            bcx = datum.store_to(bcx, lldest);
+                            if common::type_is_fat_ptr(bcx.tcx(), tupled_arg_ty) {
+                                let data = get_param(bcx.fcx.llfn, idx);
+                                let extra = get_param(bcx.fcx.llfn, idx + 1);
+                                Store(bcx, data, expr::get_dataptr(bcx, lldest));
+                                Store(bcx, extra, expr::get_len(bcx, lldest));
+                                idx += 2;
+                            } else {
+                                let datum = datum::Datum::new(
+                                    get_param(bcx.fcx.llfn, idx),
+                                    tupled_arg_ty,
+                                    arg_kind(bcx.fcx, tupled_arg_ty));
+                                idx += 1;
+                                bcx = datum.store_to(bcx, lldest);
+                            };
                         }
                         bcx
                     }));
@@ -1566,7 +1595,7 @@ pub fn trans_closure<'a, 'b, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
         }
         _ => {
             let arg_tys = untuple_arguments_if_necessary(ccx, &monomorphized_arg_types, abi);
-            create_datums_for_fn_args(&fcx, &arg_tys)
+            create_datums_for_fn_args(bcx, &arg_tys)
         }
     };
 
@@ -1773,7 +1802,7 @@ fn trans_enum_variant_or_tuple_like_struct<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx
         ty::erase_late_bound_regions(
             ccx.tcx(), &ty::ty_fn_args(ctor_ty));
 
-    let arg_datums = create_datums_for_fn_args(&fcx, &arg_tys[..]);
+    let arg_datums = create_datums_for_fn_args(bcx, &arg_tys[..]);
 
     if !type_is_zero_size(fcx.ccx, result_ty.unwrap()) {
         let dest = fcx.get_ret_slot(bcx, result_ty, "eret_slot");