Teach ValueTracking how to look through GlobalAliases. GlobalAliases are

not folded in the constant folder because the constant folder doesn't
simplify ConstantExpr operands.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81864 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 1782edee7b..9494a2f4c5 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Constants.h"
 #include "llvm/Instructions.h"
 #include "llvm/GlobalVariable.h"
+#include "llvm/GlobalAlias.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Operator.h"
@@ -105,6 +106,17 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     KnownOne.clear();
     return;
   }
+  // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
+  // the bits of its aliasee.
+  if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+    if (GA->mayBeOverridden()) {
+      KnownZero.clear(); KnownOne.clear();
+    } else {
+      ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne,
+                        TD, Depth+1);
+    }
+    return;
+  }
 
   KnownZero.clear(); KnownOne.clear();   // Start out not knowing anything.