Local: fix debug output of replaceDominatedUsesWith()

[artagnon]

Summary

The debug output of replaceDominatedUsesWith() prints incorrect
information, and the user is left confused about what exactly was
replaced. Fix this.

[RKSimon]

Any chance of a test case?

[artagnon]

Add test.

[nikic]

llvm/lib/Transforms/Utils/Local.cpp

2899

If you're already here, I think this should either print *From or From->printAsOperand(dbgs()) (the former prints the whole instruction, the latter just the name, but in a way that e.g. also works if it's an unnamed instruction).

llvm/test/Transforms/Util/local-dbg-print.ll

1 ↗

(On Diff #544356)

This needs REQUIRES: asserts.

[artagnon]

Address review comments by @nikic.

[nikic]

LG

llvm/lib/Transforms/Utils/Local.cpp

2901

as -> with?

llvm/lib/Transforms/Utils/Local.cpp

static unsigned replaceDominatedUsesWith(Value *From, Value *To,
                                          const RootType &Root,
                                          const DominatesFn &Dominates) {
   assert(From->getType() == To->getType());
 
   unsigned Count = 0;
   for (Use &U : llvm::make_early_inc_range(From->uses())) {
     if (!Dominates(Root, U))
       continue;
-    U.set(To);
     LLVM_DEBUG(dbgs() << "Replace dominated use of '" << From->getName()
-                      << "' as " << *To << " in " << *U << "\n");
+                      << "' as " << *To << " in " << *U.getUser() << "\n");
+    U.set(To);
     ++Count;
   }
   return Count;
 }
 
 unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) {
    assert(From->getType() == To->getType());
    auto *BB = From->getParent();