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[mir-opt] Allow debuginfo to be generated for a constant or a Place

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Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that `SimplifyLocals` cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The `ConstProp` pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later `SimplifyLocals` pass to remove the local.
This commit is contained in:
Wesley Wiser 2020-05-30 15:02:32 -04:00
parent b776d1c3e3
commit 01aec8d185
23 changed files with 406 additions and 127 deletions
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5
compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
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@ -1409,10 +1409,11 @@ fn generator_layout_and_saved_local_names(
let state_arg = mir::Local::new(1);
for var in &body.var_debug_info {
if var.place.local != state_arg {
let place = if let mir::VarDebugInfoContents::Place(p) = var.value { p } else { continue };
if place.local != state_arg {
continue;
}
match var.place.projection[..] {
match place.projection[..] {
[
// Deref of the `Pin<&mut Self>` state argument.
mir::ProjectionElem::Field(..),