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rustc_mir::transform::simplify - remove nops first

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Removing nops can allow more basic blocks to be merged, but merging
basic blocks can't allow for more nops to be removed, so we should
remove nops first.

This doesn't matter *that* much, because normally we run SimplifyCfg
several times, but there's no reason not to do it.
This commit is contained in:
Ariel Ben-Yehuda 2017-08-01 00:10:46 +03:00
parent ca3105cfdf
commit 5b99523de9
2 changed files with 10 additions and 16 deletions
Download patch file Download diff file Expand all files Collapse all files

4
src/librustc_mir/transform/simplify.rs
View file

@ -105,6 +105,8 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
}
pub fn simplify(mut self) {
self.strip_nops();
loop {
let mut changed = false;
@ -141,8 +143,6 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
if !changed { break }
}
self.strip_nops()
}
// Collapse a goto chain starting from `start`

22
src/test/mir-opt/basic_assignment.rs
View file

@ -50,10 +50,10 @@ fn main() {
// StorageLive(_5);
// StorageLive(_6);
// _6 = _4;
// replace(_5 <- _6) -> [return: bb1, unwind: bb7];
// replace(_5 <- _6) -> [return: bb1, unwind: bb5];
// }
// bb1: {
// drop(_6) -> [return: bb8, unwind: bb5];
// drop(_6) -> [return: bb6, unwind: bb4];
// }
// bb2: {
// resume;
@ -62,27 +62,21 @@ fn main() {
// drop(_4) -> bb2;
// }
// bb4: {
// goto -> bb3;
// drop(_5) -> bb3;
// }
// bb5: {
// drop(_5) -> bb4;
// drop(_6) -> bb4;
// }
// bb6: {
// goto -> bb5;
// }
// bb7: {
// drop(_6) -> bb6;
// }
// bb8: {
// StorageDead(_6);
// _0 = ();
// drop(_5) -> [return: bb9, unwind: bb3];
// drop(_5) -> [return: bb7, unwind: bb3];
// }
// bb9: {
// bb7: {
// StorageDead(_5);
// drop(_4) -> bb10;
// drop(_4) -> bb8;
// }
// bb10: {
// bb8: {
// StorageDead(_4);
// StorageDead(_2);
// StorageDead(_1);