🐛 shortestSWAPsBetween returns one SWAP too many (#1395)

MatthiasReumann · web-flow · commit 853eb225f434 · 2025-12-18T09:49:51.000+01:00
diff --git a/mlir/lib/Dialect/MQTOpt/Transforms/Transpilation/Architecture.cpp b/mlir/lib/Dialect/MQTOpt/Transforms/Transpilation/Architecture.cpp
@@ -38,13 +38,13 @@ Architecture::shortestSWAPsBetween(uint32_t u, uint32_t v) const {
   }
 
   llvm::SmallVector<std::pair<uint32_t, uint32_t>> swaps;
-  uint32_t curr = v;
   uint32_t last = v;
+  uint32_t curr = prev_[u][v];
 
   while (curr != u) {
-    curr = prev_[u][curr];
-    swaps.emplace_back(last, curr);
+    swaps.emplace_back(last, curr); // Insert SWAP(last, curr).
     last = curr;
+    curr = prev_[u][curr];
   }
 
   return swaps;

Original file line number	Diff line number	Diff line change
`@@ -38,13 +38,13 @@ Architecture::shortestSWAPsBetween(uint32_t u, uint32_t v) const {`
`38`	`38`	`}`
`39`	`39`
`40`	`40`	`llvm::SmallVector<std::pair<uint32_t, uint32_t>> swaps;`
`41`		`- uint32_t curr = v;`
`42`	`41`	`uint32_t last = v;`
	`42`	`+ uint32_t curr = prev_[u][v];`
`43`	`43`
`44`	`44`	`while (curr != u) {`
`45`		`- curr = prev_[u][curr];`
`46`		`- swaps.emplace_back(last, curr);`
	`45`	`+ swaps.emplace_back(last, curr); // Insert SWAP(last, curr).`
`47`	`46`	`last = curr;`
	`47`	`+ curr = prev_[u][curr];`
`48`	`48`	`}`
`49`	`49`
`50`	`50`	`return swaps;`