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

[Charles Davis]

Incorporate @reames' and @chandlerc's recommendations. In particular:

- Hoist the MDBuilder object out of the loop.
- Break early in the pointer type case; this eliminates an `else`.

Also:

- Add a FIXME for `!range` -> `!nonnull' MD.


http://reviews.llvm.org/D7621

Files:
  lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  test/Transforms/InstCombine/loadstore-metadata.ll

Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ 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 @@
   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 +337,24 @@
       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()) {
+        const auto *ITy = cast<IntegerType>(NewTy)
+        NewLoad->setMetadata(LLVMContext::MD_range,
+                             MDB.createRange(APInt(ITy->getBitWidth(), 1),
+                                             ITy->getMask()));
+      }
       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;
     }
   }
Index: test/Transforms/InstCombine/loadstore-metadata.ll
===================================================================
--- test/Transforms/InstCombine/loadstore-metadata.ll
+++ test/Transforms/InstCombine/loadstore-metadata.ll
@@ -82,21 +82,21 @@
 
 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.
 ;
 ; 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
 }
 
+; CHECK: ![[MD]] = !{i64 1, i64 -1}
 !0 = !{ !1, !1, i64 0 }
 !1 = !{ !1 }
 !2 = !{ !2, !1 }

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