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

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();

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

+; RUN: opt -passes=gvn -debug-only=local -disable-output 2>&1 < %s | FileCheck %s
+
+define void @replaceDominatedUsesWith_debug(ptr nocapture writeonly %a, i32 %beam) {
+; CHECK: Replace dominated use of 'indvars.iv' as   %0 = zext i32 %beam to i64 in   %1 = shl nuw nsw i64 %indvars.iv, 1
+entry:
+  %0 = zext i32 %beam to i64
+  br label %for.body
+
+for.cond.cleanup:                                 ; preds = %for.inc
+  ret void
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.inc ]
+  %cmp1 = icmp eq i64 %indvars.iv, %0
+  br i1 %cmp1, label %if.then, label %if.else
+
+if.then:                                          ; preds = %for.body
+  %1 = shl nuw nsw i64 %indvars.iv, 1
+  %arrayidx = getelementptr inbounds i32, ptr %a, i64 %1
+  store i32 0, ptr %arrayidx, align 4
+  br label %for.inc
+
+if.else:                                          ; preds = %for.body
+  %2 = shl nuw nsw i64 %indvars.iv, 1
+  %arrayidx4 = getelementptr inbounds i32, ptr %a, i64 %2
+  store i32 1, ptr %arrayidx4, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %if.then, %if.else
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 10000
+  br i1 %exitcond.not, label %for.cond.cleanup, label %for.body
+}