[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.

1 files changed, 6 insertions, 7 deletions

diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index d7fee60..5caed51 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -1414,6 +1414,10 @@ static void WriteOptimizationInfo(raw_ostream &Out, const User *U) {
   } else if (const GEPOperator *GEP = dyn_cast<GEPOperator>(U)) {
     if (GEP->isInBounds())
       Out << " inbounds";
+    if (auto InRange = GEP->getInRange()) {
+      Out << " inrange(" << InRange->getLower() << ", " << InRange->getUpper()
+          << ")";
+    }
   } else if (const auto *NNI = dyn_cast<PossiblyNonNegInst>(U)) {
     if (NNI->hasNonNeg())
       Out << " nneg";
@@ -1691,18 +1695,13 @@ static void WriteConstantInternal(raw_ostream &Out, const Constant *CV,
       Out << ' ' << static_cast<CmpInst::Predicate>(CE->getPredicate());
     Out << " (";
 
-    std::optional<unsigned> InRangeOp;
     if (const GEPOperator *GEP = dyn_cast<GEPOperator>(CE)) {
       WriterCtx.TypePrinter->print(GEP->getSourceElementType(), Out);
       Out << ", ";
-      InRangeOp = GEP->getInRangeIndex();
-      if (InRangeOp)
-        ++*InRangeOp;
     }
 
-    for (User::const_op_iterator OI=CE->op_begin(); OI != CE->op_end(); ++OI) {
-      if (InRangeOp && unsigned(OI - CE->op_begin()) == *InRangeOp)
-        Out << "inrange ";
+    for (User::const_op_iterator OI = CE->op_begin(); OI != CE->op_end();
+         ++OI) {
       WriterCtx.TypePrinter->print((*OI)->getType(), Out);
       Out << ' ';
       WriteAsOperandInternal(Out, *OI, WriterCtx);