[IC] Turn non-null MD on pointer loads to range MD on integer loads.

Summary:
This change fixes the FIXME that you recently added when you committed
(a modified version of) my patch.  When `InstCombine` combines a load and
store of an pointer to those of an equivalently-sized integer, it currently
drops any `!nonnull` metadata that might be present.  This change replaces
`!nonnull` metadata with `!range !{ 1, -1 }` metadata instead.

Reviewers: chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D7621

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230462 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/MDBuilder.h

@@ -67,6 +67,9 @@ public:
   /// \brief Return metadata describing the range [Lo, Hi).
   MDNode *createRange(const APInt &Lo, const APInt &Hi);
 
+  /// \brief Return metadata describing the range [Lo, Hi).
+  MDNode *createRange(Constant *Lo, Constant *Hi);
+
   //===------------------------------------------------------------------===//
   // AA metadata.
   //===------------------------------------------------------------------===//

lib/IR/MDBuilder.cpp

@@ -55,14 +55,18 @@ MDNode *MDBuilder::createBranchWeights(ArrayRef<uint32_t> Weights) {
 
 MDNode *MDBuilder::createRange(const APInt &Lo, const APInt &Hi) {
   assert(Lo.getBitWidth() == Hi.getBitWidth() && "Mismatched bitwidths!");
+
+  Type *Ty = IntegerType::get(Context, Lo.getBitWidth());
+  return createRange(ConstantInt::get(Ty, Lo), ConstantInt::get(Ty, Hi));
+}
+
+MDNode *MDBuilder::createRange(Constant *Lo, Constant *Hi) {
   // If the range is everything then it is useless.
   if (Hi == Lo)
     return nullptr;
 
   // Return the range [Lo, Hi).
-  Type *Ty = IntegerType::get(Context, Lo.getBitWidth());
-  Metadata *Range[2] = {createConstant(ConstantInt::get(Ty, Lo)),
-                        createConstant(ConstantInt::get(Ty, Hi))};
+  Metadata *Range[2] = {createConstant(Lo), createConstant(Hi)};
   return MDNode::get(Context, Range);
 }
 

lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -17,6 +17,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/MDBuilder.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
@@ -309,6 +310,7 @@ static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewT
   LoadInst *NewLoad = IC.Builder->CreateAlignedLoad(
       IC.Builder->CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
       LI.getAlignment(), LI.getName());
+  MDBuilder MDB(NewLoad->getContext());
   for (const auto &MDPair : MD) {
     unsigned ID = MDPair.first;
     MDNode *N = MDPair.second;
@@ -335,15 +337,27 @@ static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewT
       break;
 
     case LLVMContext::MD_nonnull:
-      // FIXME: We should translate this into range metadata for integer types
-      // and vice versa.
-      if (NewTy->isPointerTy())
+      // This only directly applies if the new type is also a pointer.
+      if (NewTy->isPointerTy()) {
         NewLoad->setMetadata(ID, N);
+        break;
+      }
+      // If it's integral now, translate it to !range metadata.
+      if (NewTy->isIntegerTy()) {
+        auto *ITy = cast<IntegerType>(NewTy);
+        auto *NullInt = ConstantExpr::getPtrToInt(
+            ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
+        auto *NonNullInt =
+            ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
+        NewLoad->setMetadata(LLVMContext::MD_range,
+                             MDB.createRange(NonNullInt, NullInt));
+      }
       break;
 
     case LLVMContext::MD_range:
       // FIXME: It would be nice to propagate this in some way, but the type
-      // conversions make it hard.
+      // conversions make it hard. If the new type is a pointer, we could
+      // translate it to !nonnull metadata.
       break;
     }
   }

test/Transforms/InstCombine/loadstore-metadata.ll

@@ -82,21 +82,29 @@ exit:
 
 define void @test_load_cast_combine_nonnull(float** %ptr) {
 ; We can't preserve nonnull metadata when converting a load of a pointer to
-; a load of an integer.
-; FIXME: We should really transform this into range metadata and vice versa.
+; a load of an integer. Instead, we translate it to range metadata.
+; FIXME: We should also transform range metadata back into nonnull metadata.
+; FIXME: This test is very fragile. If any LABEL lines are added after
+; this point, the test will fail, because this test depends on a metadata tuple,
+; which is always emitted at the end of the file. At some point, we should
+; consider an option to the IR printer to emit MD tuples after the function
+; that first uses them--this will allow us to refer to them like this and not
+; have the tests break. For now, this function must always come last in this
+; file, and no LABEL lines are to be added after this point.
 ;
 ; CHECK-LABEL: @test_load_cast_combine_nonnull(
-; CHECK: %[[V:.*]] = load i64* %{{.*}}
+; CHECK: %[[V:.*]] = load i64* %{{.*}}, !range ![[MD:[0-9]+]]
 ; CHECK-NOT: !nonnull
 ; CHECK: store i64 %[[V]], i64*
 entry:
   %p = load float** %ptr, !nonnull !3
   %gep = getelementptr float** %ptr, i32 42
   store float* %p, float** %gep
-
   ret void
 }
 
+; This is the metadata tuple that we reference above:
+; CHECK: ![[MD]] = !{i64 1, i64 0}
 !0 = !{ !1, !1, i64 0 }
 !1 = !{ !1 }
 !2 = !{ !2, !1 }