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librustc: Don't create extra alloca slot for by value bindings in match.

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Luqman Aden 2014-06-21 08:01:12 -04:00 committed by Luqman Aden
parent 67776ba3da
commit 94a56a3758
2 changed files with 56 additions and 116 deletions
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142
src/librustc/middle/trans/_match.rs
View File

@ -64,10 +64,8 @@
* We store information about the bound variables for each arm as part of the
* per-arm `ArmData` struct. There is a mapping from identifiers to
* `BindingInfo` structs. These structs contain the mode/id/type of the
* binding, but they also contain up to two LLVM values, called `llmatch` and
* `llbinding` respectively (the `llbinding`, as will be described shortly, is
* optional and only present for by-value bindings---therefore it is bundled
* up as part of the `TransBindingMode` type). Both point at allocas.
* binding, but they also contain an LLVM value which points at an alloca
* called `llmatch`.
*
* The `llmatch` binding always stores a pointer into the value being matched
* which points at the data for the binding. If the value being matched has
@ -83,18 +81,12 @@
* up against an identifier, we store the current pointer into the
* corresponding alloca.
*
* In addition, for each by-value binding (copy or move), we will create a
* second alloca (`llbinding`) that will hold the final value. In this
* example, that means that `d` would have this second alloca of type `D` (and
* hence `llbinding` has type `D*`).
*
* Once a pattern is completely matched, and assuming that there is no guard
* pattern, we will branch to a block that leads to the body itself. For any
* by-value bindings, this block will first load the ptr from `llmatch` (the
* one of type `D*`) and copy/move the value into `llbinding` (the one of type
* `D`). The second alloca then becomes the value of the local variable. For
* by ref bindings, the value of the local variable is simply the first
* alloca.
* one of type `D*`) and then load a second time to get the actual value (the
* one of type `D`). For by ref bindings, the value of the local variable is
* simply the first alloca.
*
* So, for the example above, we would generate a setup kind of like this:
*
@ -102,13 +94,13 @@
* | Entry |
* +-------+
* |
* +-------------------------------------------+
* | llmatch_c = (addr of first half of tuple) |
* | llmatch_d = (addr of first half of tuple) |
* +-------------------------------------------+
* +--------------------------------------------+
* | llmatch_c = (addr of first half of tuple) |
* | llmatch_d = (addr of second half of tuple) |
* +--------------------------------------------+
* |
* +--------------------------------------+
* | *llbinding_d = **llmatch_dlbinding_d |
* | *llbinding_d = **llmatch_d |
* +--------------------------------------+
*
* If there is a guard, the situation is slightly different, because we must
@ -127,22 +119,20 @@
* +-------------------------------------------+
* |
* +-------------------------------------------------+
* | *llbinding_d = **llmatch_dlbinding_d |
* | *llbinding_d = **llmatch_d |
* | check condition |
* | if false { free *llbinding_d, goto next case } |
* | if false { goto next case } |
* | if true { goto body } |
* +-------------------------------------------------+
*
* The handling for the cleanups is a bit... sensitive. Basically, the body
* is the one that invokes `add_clean()` for each binding. During the guard
* evaluation, we add temporary cleanups and revoke them after the guard is
* evaluated (it could fail, after all). Presuming the guard fails, we drop
* the various values we copied explicitly. Note that guards and moves are
* evaluated (it could fail, after all). Note that guards and moves are
* just plain incompatible.
*
* Some relevant helper functions that manage bindings:
* - `create_bindings_map()`
* - `store_non_ref_bindings()`
* - `insert_lllocals()`
*
*
@ -215,7 +205,6 @@ use middle::trans::datum;
use middle::trans::datum::*;
use middle::trans::expr::Dest;
use middle::trans::expr;
use middle::trans::glue;
use middle::trans::tvec;
use middle::trans::type_of;
use middle::trans::debuginfo;
@ -362,8 +351,8 @@ fn variant_opt(bcx: &Block, pat_id: ast::NodeId) -> Opt {
}
#[deriving(Clone)]
enum TransBindingMode {
TrByValue(/*llbinding:*/ ValueRef),
pub enum TransBindingMode {
TrByValue,
TrByRef,
}
@ -376,12 +365,12 @@ enum TransBindingMode {
* - `id` is the node id of the binding
* - `ty` is the Rust type of the binding */
#[deriving(Clone)]
struct BindingInfo {
llmatch: ValueRef,
trmode: TransBindingMode,
id: ast::NodeId,
span: Span,
ty: ty::t,
pub struct BindingInfo {
pub llmatch: ValueRef,
pub trmode: TransBindingMode,
pub id: ast::NodeId,
pub span: Span,
pub ty: ty::t,
}
type BindingsMap = HashMap<Ident, BindingInfo>;
@ -1260,41 +1249,6 @@ fn compare_values<'a>(
}
}
fn store_non_ref_bindings<'a>(
bcx: &'a Block<'a>,
bindings_map: &BindingsMap,
opt_cleanup_scope: Option<cleanup::ScopeId>)
-> &'a Block<'a>
{
/*!
* For each copy/move binding, copy the value from the value being
* matched into its final home. This code executes once one of
* the patterns for a given arm has completely matched. It adds
* cleanups to the `opt_cleanup_scope`, if one is provided.
*/
let fcx = bcx.fcx;
let mut bcx = bcx;
for (_, &binding_info) in bindings_map.iter() {
match binding_info.trmode {
TrByValue(lldest) => {
let llval = Load(bcx, binding_info.llmatch); // get a T*
let datum = Datum::new(llval, binding_info.ty, Lvalue);
bcx = datum.store_to(bcx, lldest);
match opt_cleanup_scope {
None => {}
Some(s) => {
fcx.schedule_drop_mem(s, lldest, binding_info.ty);
}
}
}
TrByRef => {}
}
}
return bcx;
}
fn insert_lllocals<'a>(bcx: &'a Block<'a>,
bindings_map: &BindingsMap,
cleanup_scope: cleanup::ScopeId)
@ -1308,9 +1262,8 @@ fn insert_lllocals<'a>(bcx: &'a Block<'a>,
for (&ident, &binding_info) in bindings_map.iter() {
let llval = match binding_info.trmode {
// By value bindings: use the stack slot that we
// copied/moved the value into
TrByValue(lldest) => lldest,
// By value bindings: load from the ptr into the matched value
TrByValue => Load(bcx, binding_info.llmatch),
// By ref binding: use the ptr into the matched value
TrByRef => binding_info.llmatch
@ -1327,9 +1280,7 @@ fn insert_lllocals<'a>(bcx: &'a Block<'a>,
if bcx.sess().opts.debuginfo == FullDebugInfo {
debuginfo::create_match_binding_metadata(bcx,
ident,
binding_info.id,
binding_info.span,
datum);
binding_info);
}
}
bcx
@ -1355,11 +1306,8 @@ fn compile_guard<'a, 'b>(
// scope for any non-ref bindings we create.
let temp_scope = bcx.fcx.push_custom_cleanup_scope();
let mut bcx = bcx;
bcx = store_non_ref_bindings(bcx, &data.bindings_map,
Some(cleanup::CustomScope(temp_scope)));
bcx = insert_lllocals(bcx, &data.bindings_map,
cleanup::CustomScope(temp_scope));
let mut bcx = insert_lllocals(bcx, &data.bindings_map,
cleanup::CustomScope(temp_scope));
let val = unpack_datum!(bcx, expr::trans(bcx, guard_expr));
let val = val.to_llbool(bcx);
@ -1370,9 +1318,10 @@ fn compile_guard<'a, 'b>(
bcx.fcx.pop_custom_cleanup_scope(temp_scope);
return with_cond(bcx, Not(bcx, val), |bcx| {
// Guard does not match: free the values we copied,
// and remove all bindings from the lllocals table
let bcx = drop_bindings(bcx, data);
// Guard does not match: remove all bindings from the lllocals table
for (_, &binding_info) in data.bindings_map.iter() {
bcx.fcx.lllocals.borrow_mut().remove(&binding_info.id);
}
match chk {
// If the default arm is the only one left, move on to the next
// condition explicitly rather than (possibly) falling back to
@ -1386,21 +1335,6 @@ fn compile_guard<'a, 'b>(
};
bcx
});
fn drop_bindings<'a>(bcx: &'a Block<'a>, data: &ArmData)
-> &'a Block<'a> {
let mut bcx = bcx;
for (_, &binding_info) in data.bindings_map.iter() {
match binding_info.trmode {
TrByValue(llval) => {
bcx = glue::drop_ty(bcx, llval, binding_info.ty);
}
TrByRef => {}
}
bcx.fcx.lllocals.borrow_mut().remove(&binding_info.id);
}
return bcx;
}
}
fn compile_submatch<'a, 'b>(
@ -1836,10 +1770,10 @@ fn create_bindings_map(bcx: &Block, pat: Gc<ast::Pat>) -> BindingsMap {
// in this case, the final type of the variable will be T,
// but during matching we need to store a *T as explained
// above
llmatch = alloca(bcx, llvariable_ty.ptr_to(), "__llmatch");
trmode = TrByValue(alloca(bcx,
llvariable_ty,
bcx.ident(ident).as_slice()));
llmatch = alloca(bcx,
llvariable_ty.ptr_to(),
bcx.ident(ident).as_slice());
trmode = TrByValue;
}
ast::BindByRef(_) => {
llmatch = alloca(bcx,
@ -1925,14 +1859,6 @@ fn trans_match_inner<'a>(scope_cx: &'a Block<'a>,
for arm_data in arm_datas.iter() {
let mut bcx = arm_data.bodycx;
// If this arm has a guard, then the various by-value bindings have
// already been copied into their homes. If not, we do it here. This
// is just to reduce code space. See extensive comment at the start
// of the file for more details.
if arm_data.arm.guard.is_none() {
bcx = store_non_ref_bindings(bcx, &arm_data.bindings_map, None);
}
// insert bindings into the lllocals map and add cleanups
let cleanup_scope = fcx.push_custom_cleanup_scope();
bcx = insert_lllocals(bcx, &arm_data.bindings_map,

30
src/librustc/middle/trans/debuginfo.rs
View File

@ -187,8 +187,8 @@ use metadata::csearch;
use middle::subst;
use middle::trans::adt;
use middle::trans::common::*;
use middle::trans::datum::{Datum, Lvalue};
use middle::trans::machine;
use middle::trans::_match::{BindingInfo, TrByValue, TrByRef};
use middle::trans::type_of;
use middle::trans::type_::Type;
use middle::trans;
@ -938,22 +938,36 @@ pub fn create_captured_var_metadata(bcx: &Block,
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_match_binding_metadata(bcx: &Block,
variable_ident: ast::Ident,
node_id: ast::NodeId,
span: Span,
datum: Datum<Lvalue>) {
binding: BindingInfo) {
if fn_should_be_ignored(bcx.fcx) {
return;
}
let scope_metadata = scope_metadata(bcx.fcx, node_id, span);
let scope_metadata = scope_metadata(bcx.fcx, binding.id, binding.span);
let aops = unsafe {
[llvm::LLVMDIBuilderCreateOpDeref(bcx.ccx().int_type.to_ref())]
};
// Regardless of the actual type (`T`) we're always passed the stack slot (alloca)
// for the binding. For ByRef bindings that's a `T*` but for ByValue bindings we
// actually have `T**`. So to get the actual variable we need to dereference once
// more.
let var_type = match binding.trmode {
TrByValue => IndirectVariable {
alloca: binding.llmatch,
address_operations: aops
},
TrByRef => DirectVariable {
alloca: binding.llmatch
}
};
declare_local(bcx,
variable_ident,
datum.ty,
binding.ty,
scope_metadata,
DirectVariable { alloca: datum.val },
var_type,
LocalVariable,
span);
binding.span);
}
/// Creates debug information for the given function argument.