Canonicalize addrspacecast ConstExpr between different pointer types

As a follow-up to r210375 which canonicalizes addrspacecast
instructions, this patch canonicalizes addrspacecast constant
expressions.

Given clang uses ConstantExpr::getAddrSpaceCast to emit addrspacecast
cosntant expressions, this patch is also a step towards having the
frontend emit canonicalized addrspacecasts.

Piggyback a minor refactor in InstCombineCasts.cpp

Update three affected tests in addrspacecast-alias.ll,
access-non-generic.ll and constant-fold-gep.ll and added one new test in
constant-fold-address-space-pointer.ll

llvm-svn: 211004

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 706e66fb422..c23ab71eaf3 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -529,7 +529,10 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
       // Try hard to fold cast of cast because they are often eliminable.
       if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy))
         return ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy);
-    } else if (CE->getOpcode() == Instruction::GetElementPtr) {
+    } else if (CE->getOpcode() == Instruction::GetElementPtr &&
+               // Do not fold addrspacecast (gep 0, .., 0). It might make the
+               // addrspacecast uncanonicalized.
+               opc != Instruction::AddrSpaceCast) {
       // If all of the indexes in the GEP are null values, there is no pointer
       // adjustment going on.  We might as well cast the source pointer.
       bool isAllNull = true;