Improve dead code elimination

Author: Wilfred

CHANGELOG.md

@@ -8,6 +8,9 @@ binaries are no longer stripped by default.
 Stripping is now done during linking, rather than shelling out to
 `strip`. This is faster and more robust.
 
+Improved dead code elimination after multiply loops, e.g. `[>++<-][-]`
+is equivalent to `[>++<-]`.
+
 # v1.10.0
 
 Updated to LLVM 13.

src/peephole.rs

@@ -379,15 +379,14 @@ fn remove_dead_loops(instrs: Vec<AstNode>) -> Vec<AstNode> {
             if let Some(prev_change_index) = previous_cell_change(&instrs, index) {
                 let prev_instr = &instrs[prev_change_index];
                 // If the previous instruction set to zero, our loop is dead.
-                // TODO: MultiplyMove also zeroes the current cell.
                 // TODO: define an is_set_zero() helper.
                 if matches!(
                     prev_instr,
                     Set {
                         amount: Wrapping(0),
                         offset: 0,
                         ..
-                    }
+                    } | MultiplyMove { .. }
                 ) {
                     return false;
                 }