[MemoryBuiltins][FIX] Adjust index type size properly wrt. AS casts

[jdoerfert]

Summary

Use existing functionality to strip constant offsets that works well
with AS casts and avoids the code duplication.

Since we strip AS casts during the computation of the offset we also
need to adjust the APInt properly to avoid mismatches in the bit width.
This code ensures the caller of compute sees APInts that match the
index type size of the value passed to compute, not the value result
of the strip pointer cast.

[jdoerfert]

Fix comments

[jdoerfert]

llvm/lib/Analysis/MemoryBuiltins.cpp

588

Here, and elsewhere, we could probably give up only on the problematic part (offset vs size).

[arsenm]

llvm/lib/Analysis/MemoryBuiltins.cpp

578–583

There are several flavors of stripPointerCasts. Why isn't this using stripAndAccumulateConstantOffsets?

[jdoerfert]

Use existing strip and accumulate

[jdoerfert]

Remove assertion that does not hold (non-constant GEPs can exist)

[nikic]

llvm/lib/Analysis/MemoryBuiltins.cpp

612

Constant GEPs can have constant expression offsets, which will not be stripped.

[jdoerfert]

llvm/lib/Analysis/MemoryBuiltins.cpp

612

Good point. I'll remove the assertion, nothing we can do with those otherwise.

[jdoerfert]

remove constant expr case and assert

[jdoerfert]

Re-introduce the former bit width adjustment. This passes all unit tests that
the strip change alone failed.

[arsenm]

Missing tests?

[jdoerfert]

Add test

[jdoerfert]

Add check lines

[jdoerfert]

Add test to correct (=latest) version of the patch

[arsenm]

llvm/test/Transforms/InstCombine/builtin-dynamic-object-size.ll

175 ↗

(On Diff #406466)

doesn't cover the special case constantexpr case?

[jdoerfert]

Add second test with constexpr gep & as cast

llvm/include/llvm/Analysis/MemoryBuiltins.h

public:
   // These are "private", except they can't actually be made private. Only
   // compute() should be used by external users.
   SizeOffsetType visitAllocaInst(AllocaInst &I);
   SizeOffsetType visitArgument(Argument &A);
   SizeOffsetType visitCallBase(CallBase &CB);
   SizeOffsetType visitConstantPointerNull(ConstantPointerNull&);
   SizeOffsetType visitExtractElementInst(ExtractElementInst &I);
   SizeOffsetType visitExtractValueInst(ExtractValueInst &I);
-  SizeOffsetType visitGEPOperator(GEPOperator &GEP);
   SizeOffsetType visitGlobalAlias(GlobalAlias &GA);
   SizeOffsetType visitGlobalVariable(GlobalVariable &GV);
   SizeOffsetType visitIntToPtrInst(IntToPtrInst&);
   SizeOffsetType visitLoadInst(LoadInst &I);
   SizeOffsetType visitPHINode(PHINode&);
   SizeOffsetType visitSelectInst(SelectInst &I);
   SizeOffsetType visitUndefValue(UndefValue&);
   SizeOffsetType visitInstruction(Instruction &I);
 
 private:
+  SizeOffsetType computeImpl(Value *V);
   bool CheckedZextOrTrunc(APInt &I);
 };
 
 using SizeOffsetEvalType = std::pair<Value *, Value *>;
 
 /// Evaluate the size and offset of an object pointed to by a Value*.
 /// May create code to compute the result at run-time.
 class ObjectSizeOffsetEvaluator

llvm/lib/Analysis/MemoryBuiltins.cpp

ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout &DL,
     : DL(DL), TLI(TLI), Options(Options) {
   // Pointer size must be rechecked for each object visited since it could have
   // a different address space.
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
   IntTyBits = DL.getIndexTypeSizeInBits(V->getType());
   Zero = APInt::getZero(IntTyBits);
 
-  V = V->stripPointerCasts();
+  APInt Offset(IntTyBits, 0);
+  V = V->stripAndAccumulateConstantOffsets(DL, Offset, /* AllowNonInbounds */ true, /* AllowInvariantGroup */ true);
+  if (Offset.isZero())
+    return computeImpl(V);
+
+  SizeOffsetType SOT = computeImpl(V);
+  return {SOT.first, SOT.second + Offset};
+}
+
+SizeOffsetType ObjectSizeOffsetVisitor::computeImpl(Value *V) {
   if (Instruction *I = dyn_cast<Instruction>(V)) {
     // If we have already seen this instruction, bail out. Cycles can happen in
     // unreachable code after constant propagation.
     if (!SeenInsts.insert(I).second)
       return unknown();
 
-    if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
-      return visitGEPOperator(*GEP);
+    assert(!isa<GEPOperator>(V) && "GEPs should have been stripped already");
     return visit(*I);
   }
   if (Argument *A = dyn_cast<Argument>(V))
     return visitArgument(*A);
   if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
     return visitConstantPointerNull(*P);
   if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
     return visitGlobalAlias(*GA);
   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
     return visitGlobalVariable(*GV);
   if (UndefValue *UV = dyn_cast<UndefValue>(V))
     return visitUndefValue(*UV);
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
     if (CE->getOpcode() == Instruction::IntToPtr)
       return unknown(); // clueless
-    if (CE->getOpcode() == Instruction::GetElementPtr)
-      return visitGEPOperator(cast<GEPOperator>(*CE));
+    assert(!isa<GEPOperator>(CE) && "GEPs should have been stripped already");
   }
 
   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: "
                     << *V << '\n');
   return unknown();
 }
 
 bool ObjectSizeOffsetVisitor::CheckedZextOrTrunc(APInt &I) {
   return ::CheckedZextOrTrunc(I, IntTyBits);

 }
 
 SizeOffsetType
 ObjectSizeOffsetVisitor::visitExtractValueInst(ExtractValueInst&) {
   // Easy cases were already folded by previous passes.
   return unknown();
 }
 
-SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
-  SizeOffsetType PtrData = compute(GEP.getPointerOperand());
-  APInt Offset(DL.getIndexTypeSizeInBits(GEP.getPointerOperand()->getType()), 0);
-  if (!bothKnown(PtrData) || !GEP.accumulateConstantOffset(DL, Offset))
-    return unknown();
-
-  return std::make_pair(PtrData.first, PtrData.second + Offset);
-}
-
 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalAlias(GlobalAlias &GA) {
   if (GA.isInterposable())
     return unknown();
   return compute(GA.getAliasee());
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV){
   if (!GV.hasDefinitiveInitializer())