IR: Don't constant fold GEP bitcasts between different address spaces

PR15262 reported a bug where the following instruction:

  i8 getelementptr inbounds i8* bitcast ([4 x i8] addrspace(12)* @buf to i8*),
                                i32 2

was getting folded into:

  addrspace(12)* getelementptr inbounds ([4 x i8] addrspace(12)* @buf, i32 0,
                                        i32 2)

This caused instcombine to crash because the original instruction and
the folded instruction have different types.  The issue was fixed by
disallowing bitcasts between different address spaces to be folded away.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176156 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 13 deletions

diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp
index a5a9d9f3a7..bf93d4f956 100644
--- a/lib/IR/ConstantFold.cpp
+++ b/lib/IR/ConstantFold.cpp
@@ -1971,21 +1971,30 @@ static Constant *ConstantFoldGetElementPtrImpl(Constant *C,
       }
     }
 
-    // Implement folding of:
-    //    i32* getelementptr ([2 x i32]* bitcast ([3 x i32]* %X to [2 x i32]*),
-    //                        i64 0, i64 0)
-    // To: i32* getelementptr ([3 x i32]* %X, i64 0, i64 0)
+    // Attempt to fold casts to the same type away.  For example, folding:
     //
+    //   i32* getelementptr ([2 x i32]* bitcast ([3 x i32]* %X to [2 x i32]*),
+    //                       i64 0, i64 0)
+    // into:
+    //
+    //   i32* getelementptr ([3 x i32]* %X, i64 0, i64 0)
+    //
+    // Don't fold if the cast is changing address spaces.
     if (CE->isCast() && Idxs.size() > 1 && Idx0->isNullValue()) {
-      if (PointerType *SPT =
-          dyn_cast<PointerType>(CE->getOperand(0)->getType()))
-        if (ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType()))
-          if (ArrayType *CAT =
-        dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType()))
-            if (CAT->getElementType() == SAT->getElementType())
-              return
-                ConstantExpr::getGetElementPtr((Constant*)CE->getOperand(0),
-                                               Idxs, inBounds);
+      PointerType *SrcPtrTy =
+        dyn_cast<PointerType>(CE->getOperand(0)->getType());
+      PointerType *DstPtrTy = dyn_cast<PointerType>(CE->getType());
+      if (SrcPtrTy && DstPtrTy) {
+        ArrayType *SrcArrayTy =
+          dyn_cast<ArrayType>(SrcPtrTy->getElementType());
+        ArrayType *DstArrayTy =
+          dyn_cast<ArrayType>(DstPtrTy->getElementType());
+        if (SrcArrayTy && DstArrayTy
+            && SrcArrayTy->getElementType() == DstArrayTy->getElementType()
+            && SrcPtrTy->getAddressSpace() == DstPtrTy->getAddressSpace())
+          return ConstantExpr::getGetElementPtr((Constant*)CE->getOperand(0),
+                                                Idxs, inBounds);
+      }
     }
   }