From 0f46e31cfbf415fcd3d3ce121bef94e92c6ccfc8 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Wed, 20 Mar 2024 10:59:45 +0100
Subject: [IR] Change representation of getelementptr inrange (#84341)

As part of the migration to ptradd
(https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699),
we need to change the representation of the `inrange` attribute, which
is used for vtable splitting.

Currently, inrange is specified as follows:

```
getelementptr inbounds ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, inrange i32 1, i64 2)
```

The `inrange` is placed on a GEP index, and all accesses must be "in
range" of that index. The new representation is as follows:

```
getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, i32 1, i64 2)
```

This specifies which offsets are "in range" of the GEP result. The new
representation will continue working when canonicalizing to ptradd
representation:

```
getelementptr inbounds inrange(-16, 16) (i8, ptr @vt, i64 48)
```

The inrange offsets are relative to the return value of the GEP. An
alternative design could make them relative to the source pointer
instead. The result-relative format was chosen on the off-chance that we
want to extend support to non-constant GEPs in the future, in which case
this variant is more expressive.

This implementation "upgrades" the old inrange representation in bitcode
by simply dropping it. This is a very niche feature, and I don't think
trying to upgrade it is worthwhile. Let me know if you disagree.
---
 llvm/lib/IR/Constants.cpp | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

(limited to 'llvm/lib/IR/Constants.cpp')

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 07b5bce..c17419b 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1568,7 +1568,7 @@ Constant *ConstantExpr::getWithOperands(ArrayRef<Constant *> Ops, Type *Ty,
     assert(SrcTy || (Ops[0]->getType() == getOperand(0)->getType()));
     return ConstantExpr::getGetElementPtr(
         SrcTy ? SrcTy : GEPO->getSourceElementType(), Ops[0], Ops.slice(1),
-        GEPO->isInBounds(), GEPO->getInRangeIndex(), OnlyIfReducedTy);
+        GEPO->isInBounds(), GEPO->getInRange(), OnlyIfReducedTy);
   }
   case Instruction::ICmp:
   case Instruction::FCmp:
@@ -2349,17 +2349,16 @@ Constant *ConstantExpr::getCompare(unsigned short Predicate, Constant *C1,
 
 Constant *ConstantExpr::getGetElementPtr(Type *Ty, Constant *C,
                                          ArrayRef<Value *> Idxs, bool InBounds,
-                                         std::optional<unsigned> InRangeIndex,
+                                         std::optional<ConstantRange> InRange,
                                          Type *OnlyIfReducedTy) {
   assert(Ty && "Must specify element type");
   assert(isSupportedGetElementPtr(Ty) && "Element type is unsupported!");
 
-  if (Constant *FC =
-          ConstantFoldGetElementPtr(Ty, C, InBounds, InRangeIndex, Idxs))
-    return FC;          // Fold a few common cases.
+  if (Constant *FC = ConstantFoldGetElementPtr(Ty, C, InBounds, InRange, Idxs))
+    return FC; // Fold a few common cases.
 
-  assert(GetElementPtrInst::getIndexedType(Ty, Idxs) &&
-         "GEP indices invalid!");;
+  assert(GetElementPtrInst::getIndexedType(Ty, Idxs) && "GEP indices invalid!");
+  ;
 
   // Get the result type of the getelementptr!
   Type *ReqTy = GetElementPtrInst::getGEPReturnType(C, Idxs);
@@ -2392,10 +2391,9 @@ Constant *ConstantExpr::getGetElementPtr(Type *Ty, Constant *C,
   }
 
   unsigned SubClassOptionalData = InBounds ? GEPOperator::IsInBounds : 0;
-  if (InRangeIndex && *InRangeIndex < 63)
-    SubClassOptionalData |= (*InRangeIndex + 1) << 1;
   const ConstantExprKeyType Key(Instruction::GetElementPtr, ArgVec, 0,
-                                SubClassOptionalData, std::nullopt, Ty);
+                                SubClassOptionalData, std::nullopt, Ty,
+                                InRange);
 
   LLVMContextImpl *pImpl = C->getContext().pImpl;
   return pImpl->ExprConstants.getOrCreate(ReqTy, Key);
@@ -2691,13 +2689,15 @@ const char *ConstantExpr::getOpcodeName() const {
 }
 
 GetElementPtrConstantExpr::GetElementPtrConstantExpr(
-    Type *SrcElementTy, Constant *C, ArrayRef<Constant *> IdxList, Type *DestTy)
+    Type *SrcElementTy, Constant *C, ArrayRef<Constant *> IdxList, Type *DestTy,
+    std::optional<ConstantRange> InRange)
     : ConstantExpr(DestTy, Instruction::GetElementPtr,
                    OperandTraits<GetElementPtrConstantExpr>::op_end(this) -
                        (IdxList.size() + 1),
                    IdxList.size() + 1),
       SrcElementTy(SrcElementTy),
-      ResElementTy(GetElementPtrInst::getIndexedType(SrcElementTy, IdxList)) {
+      ResElementTy(GetElementPtrInst::getIndexedType(SrcElementTy, IdxList)),
+      InRange(std::move(InRange)) {
   Op<0>() = C;
   Use *OperandList = getOperandList();
   for (unsigned i = 0, E = IdxList.size(); i != E; ++i)
@@ -2712,6 +2712,10 @@ Type *GetElementPtrConstantExpr::getResultElementType() const {
   return ResElementTy;
 }
 
+std::optional<ConstantRange> GetElementPtrConstantExpr::getInRange() const {
+  return InRange;
+}
+
 //===----------------------------------------------------------------------===//
 //                       ConstantData* implementations
 
-- 
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