[SelectionDAG][RISCV][SVE] Harden fixed offset version of ComputeValueVTs against scalable offsets.

[craig.topper]

Summary

Use getFixedValue instead of getKnownMinValue to convert TypeSize
to uint64_t. I believe this would have caught the bug fixed by
D157872.

To prevent false failures, I had to treat a scalable 0 as if it
is fixed value.

[craig.topper]

Add the whole patch.

[paulwalker-arm]

llvm/lib/CodeGen/Analysis.cpp

151

A value of zero is both fixed and scalable compatible so I think perhaps this should just always be getFixedValue() and TypeSize should be updated to allow the scalable zero case to return 0.

I also think isFixed() and isScalable() should return true for the zero case but that can be a job for later.

[craig.topper]

Sync the zero check into getFixedValue.

llvm/include/llvm/Support/TypeSize.h

 //===- TypeSize.h - Wrapper around type sizes -------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
public:
   constexpr bool isKnownMultipleOf(ScalarTy RHS) const {
     return getKnownMinValue() % RHS == 0;
   }
 
   // Return the minimum value with the assumption that the count is exact.
   // Use in places where a scalable count doesn't make sense (e.g. non-vector
   // types, or vectors in backends which don't support scalable vectors).
   constexpr ScalarTy getFixedValue() const {
-    assert(!isScalable() &&
+    assert((!isScalable() || isZero()) &&
            "Request for a fixed element count on a scalable object");
     return getKnownMinValue();
   }
 
   // For some cases, quantity ordering between scalable and fixed quantity types
   // cannot be determined at compile time, so such comparisons aren't allowed.
   //
   // e.g. <vscale x 2 x i16> could be bigger than <4 x i32> with a runtime

llvm/lib/CodeGen/Analysis.cpp

 //===-- Analysis.cpp - CodeGen LLVM IR Analysis Utilities -----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
   return ComputeValueVTs(TLI, DL, Ty, ValueVTs, Offsets, Offset);
 }
 
 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
                            Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
                            SmallVectorImpl<uint64_t> *FixedOffsets,
                            uint64_t StartingOffset) {
   TypeSize Offset = TypeSize::get(StartingOffset, Ty->isScalableTy());
+  if (FixedOffsets) {
     SmallVector<TypeSize, 4> Offsets;
-  if (FixedOffsets)
     ComputeValueVTs(TLI, DL, Ty, ValueVTs, &Offsets, Offset);
-  else
-    ComputeValueVTs(TLI, DL, Ty, ValueVTs, nullptr, Offset);
-
-  if (FixedOffsets)
     for (TypeSize Offset : Offsets)
-      FixedOffsets->push_back(Offset.getKnownMinValue());
+      FixedOffsets->push_back(Offset.getFixedValue());
+  } else {
+    ComputeValueVTs(TLI, DL, Ty, ValueVTs, nullptr, Offset);
+  }
 }
 
 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
                            Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
                            SmallVectorImpl<EVT> *MemVTs,
                            SmallVectorImpl<TypeSize> *Offsets,
                            uint64_t StartingOffset) {
   TypeSize Offset = TypeSize::get(StartingOffset, Ty->isScalableTy());
   return ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, Offsets, Offset);
 }
 
 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
                            Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
                            SmallVectorImpl<EVT> *MemVTs,
                            SmallVectorImpl<uint64_t> *FixedOffsets,
                            uint64_t StartingOffset) {
   TypeSize Offset = TypeSize::get(StartingOffset, Ty->isScalableTy());
+  if (FixedOffsets) {
     SmallVector<TypeSize, 4> Offsets;
-  if (FixedOffsets)
     ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, &Offsets, Offset);
-  else
-    ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, nullptr, Offset);
-
-  if (FixedOffsets)
     for (TypeSize Offset : Offsets)
-      FixedOffsets->push_back(Offset.getKnownMinValue());
+      FixedOffsets->push_back(Offset.getFixedValue());
+  } else {
+    ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, nullptr, Offset);
+  }
 }
 
 void llvm::computeValueLLTs(const DataLayout &DL, Type &Ty,
                             SmallVectorImpl<LLT> &ValueTys,
                             SmallVectorImpl<uint64_t> *Offsets,
                             uint64_t StartingOffset) {
   // Given a struct type, recursively traverse the elements.
   if (StructType *STy = dyn_cast<StructType>(&Ty)) {