From 4d614e1d1f964ac1dc7af0261848cf6dc63d915c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= Date: Wed, 15 Sep 2021 00:00:00 +0000 Subject: [PATCH] Do not collapse goto chains beginning with the start block If any block on a goto chain has more than one predecessor, then the new start block would have basic block predecessors. Skip the transformation for the start block altogether, to avoid violating the new invariant that the start block does not have any basic block predecessors. --- compiler/rustc_mir_transform/src/simplify.rs | 25 -------------------- 1 file changed, 25 deletions(-) diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs index e3cfd1d0afcd7..d6cd505cbb569 100644 --- a/compiler/rustc_mir_transform/src/simplify.rs +++ b/compiler/rustc_mir_transform/src/simplify.rs @@ -95,8 +95,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { pub fn simplify(mut self) { self.strip_nops(); - let mut start = START_BLOCK; - // Vec of the blocks that should be merged. We store the indices here, instead of the // statements itself to avoid moving the (relatively) large statements twice. // We do not push the statements directly into the target block (`bb`) as that is slower @@ -105,8 +103,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { loop { let mut changed = false; - self.collapse_goto_chain(&mut start, &mut changed); - for bb in self.basic_blocks.indices() { if self.pred_count[bb] == 0 { continue; @@ -149,27 +145,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { break; } } - - if start != START_BLOCK { - debug_assert!(self.pred_count[START_BLOCK] == 0); - self.basic_blocks.swap(START_BLOCK, start); - self.pred_count.swap(START_BLOCK, start); - - // pred_count == 1 if the start block has no predecessor _blocks_. - if self.pred_count[START_BLOCK] > 1 { - for (bb, data) in self.basic_blocks.iter_enumerated_mut() { - if self.pred_count[bb] == 0 { - continue; - } - - for target in data.terminator_mut().successors_mut() { - if *target == start { - *target = START_BLOCK; - } - } - } - } - } } /// This function will return `None` if