43a86f14d5
This also paves the way for unifying TargetIsa and MachBackend, since now they map one to one. In theory the two traits could be merged, which would be nice to limit the number of total concepts. Also they have quite different responsibilities, so it might be fine to keep them separate. Interestingly, this PR started as removing RegInfo from the TargetIsa trait since the adapter returned a dummy value there. From the fallout, noticed that all Display implementations didn't needed an ISA anymore (since these were only used to render ISA specific registers). Also the whole family of RegInfo / ValueLoc / RegUnit was exclusively used for the old backend, and these could be removed. Notably, some IR instructions needed to be removed, because they were using RegUnit too: this was the oddball of regfill / regmove / regspill / copy_special, which were IR instructions inserted by the old regalloc. Fare thee well!
59 lines
2.1 KiB
Rust
59 lines
2.1 KiB
Rust
//! Unreachable code elimination.
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use crate::cursor::{Cursor, FuncCursor};
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use crate::dominator_tree::DominatorTree;
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use crate::flowgraph::ControlFlowGraph;
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use crate::ir;
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use crate::timing;
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/// Eliminate unreachable code.
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///
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/// This pass deletes whole blocks that can't be reached from the entry block. It does not delete
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/// individual instructions whose results are unused.
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///
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/// The reachability analysis is performed by the dominator tree analysis.
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pub fn eliminate_unreachable_code(
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func: &mut ir::Function,
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cfg: &mut ControlFlowGraph,
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domtree: &DominatorTree,
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) {
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let _tt = timing::unreachable_code();
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let mut pos = FuncCursor::new(func);
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while let Some(block) = pos.next_block() {
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if domtree.is_reachable(block) {
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continue;
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}
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log::trace!("Eliminating unreachable {}", block);
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// Move the cursor out of the way and make sure the next lop iteration goes to the right
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// block.
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pos.prev_block();
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// Remove all instructions from `block`.
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while let Some(inst) = pos.func.layout.first_inst(block) {
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log::trace!(" - {}", pos.func.dfg.display_inst(inst));
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pos.func.layout.remove_inst(inst);
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}
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// Once the block is completely empty, we can update the CFG which removes it from any
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// predecessor lists.
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cfg.recompute_block(pos.func, block);
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// Finally, remove the block from the layout.
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pos.func.layout.remove_block(block);
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}
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// Remove all jumptable block-list contents that refer to unreachable
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// blocks; the jumptable itself must have been unused (or used only in an
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// unreachable block) if so. Note that we are not necessarily removing *all*
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// unused jumptables, because that would require computing their
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// reachability as well; we are just removing enough to clean up references
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// to deleted blocks.
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for jt_data in func.jump_tables.values_mut() {
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let invalid_ref = jt_data.iter().any(|block| !domtree.is_reachable(*block));
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if invalid_ref {
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jt_data.clear();
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}
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}
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}
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