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Fix MIR CopyPropagation errneously propagating assignments to function arguments

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sinkuu 2017-11-05 22:08:30 +09:00 • committed by Shotaro Yamada
parent c0d326f06d
commit ae5553d7b0
2 changed files with 122 additions and 0 deletions
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7
src/librustc_mir/transform/copy_prop.rs
View file

@ -99,6 +99,13 @@ impl MirPass for CopyPropagation {
dest_local);
continue
}
// Conservatively gives up if the dest is an argument,
// because there may be uses of the original argument value.
if mir.local_kind(dest_local) == LocalKind::Arg {
debug!(" Can't copy-propagate local: dest {:?} (argument)",
dest_local);
continue;
}
let dest_lvalue_def = dest_use_info.defs_and_uses.iter().filter(|lvalue_def| {
lvalue_def.context.is_mutating_use() && !lvalue_def.context.is_drop()
}).next().unwrap();

115
src/test/mir-opt/copy_propagation_arg.rs Normal file
View file

@ -0,0 +1,115 @@
// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Check that CopyPropagation does not propagate an assignment to a function argument
// (doing so can break usages of the original argument value)
fn dummy(x: u8) -> u8 {
x
}
fn foo(mut x: u8) {
// calling `dummy` to make an use of `x` that copyprop cannot eliminate
x = dummy(x); // this will assign a local to `x`
}
fn bar(mut x: u8) {
dummy(x);
x = 5;
}
fn baz(mut x: i32) {
// self-assignment to a function argument should be eliminated
x = x;
}
fn main() {
// Make sure the function actually gets instantiated.
foo(0);
bar(0);
}
// END RUST SOURCE
// START rustc.foo.CopyPropagation.before.mir
// bb0: {
// StorageLive(_2);
// StorageLive(_3);
// _3 = _1;
// _2 = const dummy(_3) -> bb1;
// }
// bb1: {
// StorageDead(_3);
// _1 = _2;
// StorageDead(_2);
// _0 = ();
// return;
// }
// END rustc.foo.CopyPropagation.before.mir
// START rustc.foo.CopyPropagation.after.mir
// bb0: {
// StorageLive(_2);
// nop;
// nop;
// _2 = const dummy(_1) -> bb1;
// }
// bb1: {
// nop;
// _1 = _2;
// StorageDead(_2);
// _0 = ();
// return;
// }
// END rustc.foo.CopyPropagation.after.mir
// START rustc.bar.CopyPropagation.before.mir
// bb0: {
// StorageLive(_3);
// _3 = _1;
// _2 = const dummy(_3) -> bb1;
// }
// bb1: {
// StorageDead(_3);
// _1 = const 5u8;
// _0 = ();
// return;
// }
// END rustc.bar.CopyPropagation.before.mir
// START rustc.bar.CopyPropagation.after.mir
// bb0: {
// nop;
// nop;
// _2 = const dummy(_1) -> bb1;
// }
// bb1: {
// nop;
// _1 = const 5u8;
// _0 = ();
// return;
// }
// END rustc.bar.CopyPropagation.after.mir
// START rustc.baz.CopyPropagation.before.mir
// bb0: {
// StorageLive(_2);
// _2 = _1;
// _1 = _2;
// StorageDead(_2);
// _0 = ();
// return;
// }
// END rustc.baz.CopyPropagation.before.mir
// START rustc.baz.CopyPropagation.after.mir
// bb0: {
// nop;
// nop;
// nop;
// nop;
// _0 = ();
// return;
// }
// END rustc.baz.CopyPropagation.after.mir