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.

llvm-svn: 176156

2 files changed, 42 insertions, 13 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index a5a9d9f3a7c..bf93d4f9566 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/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);
+      }
     }
   }
 
diff --git a/llvm/test/Other/constant-fold-gep.ll b/llvm/test/Other/constant-fold-gep.ll
index 0224e9f984c..44b66284dd7 100644
--- a/llvm/test/Other/constant-fold-gep.ll
+++ b/llvm/test/Other/constant-fold-gep.ll
@@ -447,4 +447,24 @@ define i32* @fZ() nounwind {
   ret i32* %t
 }
 
+; PR15262 - Check GEP folding with casts between address spaces.
+
+@p0 = global [4 x i8] zeroinitializer, align 1
+@p12 = addrspace(12) global [4 x i8] zeroinitializer, align 1
+
+define i8* @different_addrspace() nounwind noinline {
+; OPT: different_addrspace
+  %p = getelementptr inbounds i8* bitcast ([4 x i8] addrspace(12)* @p12 to i8*),
+                                  i32 2
+  ret i8* %p
+; OPT: ret i8* getelementptr (i8* bitcast ([4 x i8] addrspace(12)* @p12 to i8*), i32 2)
+}
+
+define i8* @same_addrspace() nounwind noinline {
+; OPT: same_addrspace
+  %p = getelementptr inbounds i8* bitcast ([4 x i8] * @p0 to i8*), i32 2
+  ret i8* %p
+; OPT: ret i8* getelementptr inbounds ([4 x i8]* @p0, i32 0, i32 2)
+}
+
 ; CHECK: attributes #0 = { nounwind }