[Debug] Add dbg.value intrinsics for PHIs created during LCSSA.
Summary:
This patch is an enhancement to propagate dbg.value information when Phis are created on behalf of LCSSA.
I noticed a case where a value carried across a loop was reported as <optimized out>.
Specifically this case:
```
int bar(int x, int y) {
return x + y;
}
int foo(int size) {
int val = 0;
for (int i = 0; i < size; ++i) {
val = bar(val, i); // Both val and i are correct
}
return val; // <optimized out>
}
```
In the above case, after all of the interesting computation completes our value
is reported as "optimized out." This change will add a dbg.value to correct this.
This patch also moves the dbg.value insertion routine from LoopRotation.cpp
into Local.cpp, so that we can share it in both places (LoopRotation and LCSSA).
Reviewers: mzolotukhin, aprantl, vsk, davide
Reviewed By: aprantl, vsk
Subscribers: dberlin, llvm-commits
Differential Revision: https://reviews.llvm.org/D42551
llvm-svn: 325926
diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
index ae0e2bb..a68448b 100644
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -43,6 +43,7 @@
#include "llvm/IR/PredIteratorCache.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
@@ -214,11 +215,15 @@
Worklist.push_back(PostProcessPN);
// Keep track of PHI nodes that we want to remove because they did not have
- // any uses rewritten.
+ // any uses rewritten. If the new PHI is used, store it so that we can
+ // try to propagate dbg.value intrinsics to it.
+ SmallVector<PHINode *, 2> NeedDbgValues;
for (PHINode *PN : AddedPHIs)
if (PN->use_empty())
PHIsToRemove.insert(PN);
-
+ else
+ NeedDbgValues.push_back(PN);
+ insertDebugValuesForPHIs(InstBB, NeedDbgValues);
Changed = true;
}
// Remove PHI nodes that did not have any uses rewritten.