IR: Don't add inbounds to GEPs of extern_weak variables

Global variables that have `extern_weak` linkage may be null, so it's
incorrect to add `inbounds` when constant folding.

This also fixes a bug when parsing global aliases, whose forward
reference placeholders are global variables with `extern_weak` linkage.
If GEPs to these aliases are encountered before the alias itself, the
GEPs would incorrectly gain the `inbounds` keyword as well.

llvm-svn: 215803

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 395ac39..9124c11 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -2144,9 +2144,10 @@ static Constant *ConstantFoldGetElementPtrImpl(Constant *C,
 
   // If all indices are known integers and normalized, we can do a simple
   // check for the "inbounds" property.
-  if (!Unknown && !inBounds &&
-      isa<GlobalVariable>(C) && isInBoundsIndices(Idxs))
-    return ConstantExpr::getInBoundsGetElementPtr(C, Idxs);
+  if (!Unknown && !inBounds)
+    if (auto *GV = dyn_cast<GlobalVariable>(C))
+      if (!GV->hasExternalWeakLinkage() && isInBoundsIndices(Idxs))
+        return ConstantExpr::getInBoundsGetElementPtr(C, Idxs);
 
   return nullptr;
 }