[ArgumentPromotion] Change use of removed argument in llvm.dbg.value to undef

Summary:
This solves PR33641.

When removing a dead argument we must also handle possibly existing calls
to llvm.dbg.value that use the removed argument. Now we change the use
of the otherwise dead argument to an undef for some other pass to cleanup
later.

If the calls are left untouched, they will later on cause errors:
 "function-local metadata used in wrong function"
since the ArgumentPromotion rewrites the code by creating a new function
with the wanted signature, but the metadata is not recreated so the new
function may then erroneously use metadata from the old function.

Reviewers: mstorsjo, rnk, arsenm

Reviewed By: rnk

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D34874

llvm-svn: 307521

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
index d8cf8d3f5da..53223ab4431 100644
--- a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -124,6 +124,10 @@ doPromotion(Function *F, SmallPtrSetImpl<Argument *> &ArgsToPromote,
     } else if (I->use_empty()) {
       // Dead argument (which are always marked as promotable)
       ++NumArgumentsDead;
+
+      // There may be remaining metadata uses of the argument for things like
+      // llvm.dbg.value. Replace them with undef.
+      I->replaceAllUsesWith(UndefValue::get(I->getType()));
     } else {
       // Okay, this is being promoted. This means that the only uses are loads
       // or GEPs which are only used by loads