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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211004 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 17 insertions, 1 deletions

diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp
index 706e66fb42..c23ab71eaf 100644
--- a/lib/IR/ConstantFold.cpp
+++ b/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;
diff --git a/lib/IR/Constants.cpp b/lib/IR/Constants.cpp
index bb8d60b234..aa26cff6a7 100644
--- a/lib/IR/Constants.cpp
+++ b/lib/IR/Constants.cpp
@@ -1698,6 +1698,19 @@ Constant *ConstantExpr::getAddrSpaceCast(Constant *C, Type *DstTy) {
   assert(CastInst::castIsValid(Instruction::AddrSpaceCast, C, DstTy) &&
          "Invalid constantexpr addrspacecast!");
 
+  // Canonicalize addrspacecasts between different pointer types by first
+  // bitcasting the pointer type and then converting the address space.
+  PointerType *SrcScalarTy = cast<PointerType>(C->getType()->getScalarType());
+  PointerType *DstScalarTy = cast<PointerType>(DstTy->getScalarType());
+  Type *DstElemTy = DstScalarTy->getElementType();
+  if (SrcScalarTy->getElementType() != DstElemTy) {
+    Type *MidTy = PointerType::get(DstElemTy, SrcScalarTy->getAddressSpace());
+    if (VectorType *VT = dyn_cast<VectorType>(DstTy)) {
+      // Handle vectors of pointers.
+      MidTy = VectorType::get(MidTy, VT->getNumElements());
+    }
+    C = getBitCast(C, MidTy);
+  }
   return getFoldedCast(Instruction::AddrSpaceCast, C, DstTy);
 }