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[const-prop] Handle Rvalue::Len

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This commit is contained in:
Wesley Wiser 2019-05-20 05:46:33 -04:00
parent 1e50e01bb7
commit dee05ab2cc
2 changed files with 46 additions and 23 deletions
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29
src/librustc_mir/transform/const_prop.rs
View file

@ -17,8 +17,7 @@ use syntax_pos::{Span, DUMMY_SP};
use rustc::ty::subst::InternalSubsts;
use rustc_data_structures::indexed_vec::IndexVec;
use rustc::ty::layout::{
LayoutOf, TyLayout, LayoutError,
HasTyCtxt, TargetDataLayout, HasDataLayout,
LayoutOf, TyLayout, LayoutError, HasTyCtxt, TargetDataLayout, HasDataLayout, Size,
};
use crate::interpret::{
@ -386,10 +385,30 @@ impl<'a, 'mir, 'tcx> ConstPropagator<'a, 'mir, 'tcx> {
this.ecx.cast(op, kind, dest.into())?;
Ok(dest.into())
})
}
},
Rvalue::Len(ref place) => {
let place = self.eval_place(&place, source_info)?;
let mplace = place.try_as_mplace().ok()?;
// FIXME(oli-obk): evaluate static/constant slice lengths
Rvalue::Len(_) => None,
if let ty::Slice(_) = mplace.layout.ty.sty {
let len = mplace.meta.unwrap().to_usize(&self.ecx).unwrap();
Some(ImmTy {
imm: Immediate::Scalar(
Scalar::from_uint(
len,
Size::from_bits(
self.tcx.sess.target.usize_ty.bit_width().unwrap() as u64
)
).into(),
),
layout: self.tcx.layout_of(self.param_env.and(self.tcx.types.usize)).ok()?,
}.into())
} else {
trace!("not slice: {:?}", mplace.layout.ty.sty);
None
}
},
Rvalue::NullaryOp(NullOp::SizeOf, ty) => {
type_size_of(self.tcx, self.param_env, ty).and_then(|n| Some(
ImmTy {

40
src/test/mir-opt/const_prop/slice_len.rs
View file

@ -1,22 +1,22 @@
fn test() -> &'static [u32] {
&[1, 2]
}
fn main() {
let x = test()[0];
(&[1u32, 2, 3] as &[u32])[1];
}
// END RUST SOURCE
// START rustc.main.ConstProp.before.mir
// bb1: {
// bb0: {
// ...
// _3 = const 0usize;
// _4 = Len((*_2));
// _5 = Lt(_3, _4);
// assert(move _5, "index out of bounds: the len is move _4 but the index is _3") -> bb2;
// _4 = &(promoted[0]: [u32; 3]);
// _3 = _4;
// _2 = move _3 as &[u32] (Pointer(Unsize));
// ...
// _6 = const 1usize;
// _7 = Len((*_2));
// _8 = Lt(_6, _7);
// assert(move _8, "index out of bounds: the len is move _7 but the index is _6") -> bb1;
// }
// bb2: {
// _1 = (*_2)[_3];
// bb1: {
// _1 = (*_2)[_6];
// ...
// return;
// }
@ -24,13 +24,17 @@ fn main() {
// START rustc.main.ConstProp.after.mir
// bb0: {
// ...
// _3 = const 0usize;
// _4 = Len((*_2));
// _5 = Lt(_3, _4);
// assert(move _5, "index out of bounds: the len is move _4 but the index is _3") -> bb2;
// _4 = const Scalar(AllocId(0).0x0) : &[u32; 3];
// _3 = const Scalar(AllocId(0).0x0) : &[u32; 3];
// _2 = move _3 as &[u32] (Pointer(Unsize));
// ...
// _6 = const 1usize;
// _7 = const 3usize;
// _8 = const true;
// assert(const true, "index out of bounds: the len is move _7 but the index is _6") -> bb1;
// }
// bb2: {
// _1 = (*_2)[_3];
// bb1: {
// _1 = (*_2)[_6];
// ...
// return;
// }