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|
//! See docs in build/expr/mod.rs
use crate::build::{BlockAnd, BlockAndExtension, Builder};
use crate::hair::*;
use rustc::middle::region;
use rustc::mir::*;
impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
/// Compile `expr` into a fresh temporary. This is used when building
/// up rvalues so as to freeze the value that will be consumed.
pub fn as_temp<M>(
&mut self,
block: BasicBlock,
temp_lifetime: Option<region::Scope>,
expr: M,
mutability: Mutability,
) -> BlockAnd<Local>
where
M: Mirror<'tcx, Output = Expr<'tcx>>,
{
let expr = self.hir.mirror(expr);
self.expr_as_temp(block, temp_lifetime, expr, mutability)
}
fn expr_as_temp(
&mut self,
mut block: BasicBlock,
temp_lifetime: Option<region::Scope>,
expr: Expr<'tcx>,
mutability: Mutability,
) -> BlockAnd<Local> {
debug!(
"expr_as_temp(block={:?}, temp_lifetime={:?}, expr={:?}, mutability={:?})",
block, temp_lifetime, expr, mutability
);
let this = self;
let expr_span = expr.span;
let source_info = this.source_info(expr_span);
if let ExprKind::Scope {
region_scope,
lint_level,
value,
} = expr.kind
{
return this.in_scope((region_scope, source_info), lint_level, block, |this| {
this.as_temp(block, temp_lifetime, value, mutability)
});
}
let expr_ty = expr.ty;
let temp = {
let mut local_decl = LocalDecl::new_temp(expr_ty, expr_span);
if mutability == Mutability::Not {
local_decl = local_decl.immutable();
}
debug!("creating temp {:?} with block_context: {:?}", local_decl, this.block_context);
// Find out whether this temp is being created within the
// tail expression of a block whose result is ignored.
if let Some(tail_info) = this.block_context.currently_in_block_tail() {
local_decl = local_decl.block_tail(tail_info);
}
this.local_decls.push(local_decl)
};
if !expr_ty.is_never() {
this.cfg.push(
block,
Statement {
source_info,
kind: StatementKind::StorageLive(temp),
},
);
}
unpack!(block = this.into(&Place::Local(temp), block, expr));
// In constants, temp_lifetime is None for temporaries that live for the
// 'static lifetime. Thus we do not drop these temporaries and simply leak them.
// This is equivalent to what `let x = &foo();` does in functions. The temporary
// is lifted to their surrounding scope. In a function that means the temporary lives
// until just before the function returns. In constants that means it outlives the
// constant's initialization value computation. Anything outliving a constant
// must have the `'static` lifetime and live forever.
// Anything with a shorter lifetime (e.g the `&foo()` in `bar(&foo())` or anything
// within a block will keep the regular drops just like runtime code.
if let Some(temp_lifetime) = temp_lifetime {
this.schedule_drop_storage_and_value(
expr_span,
temp_lifetime,
&Place::Local(temp),
expr_ty,
);
}
block.and(temp)
}
}
|
