[1/11][IR] Permit load/store/alloca for struct of the same scalable vector type

This patch-set aims to simplify the existing RVV segment load/store
intrinsics to use a type that represents a tuple of vectors instead.

To achieve this, first we need to relax the current limitation for an
aggregate type to be a target of load/store/alloca when the aggregate
type contains homogeneous scalable vector types. Then to adjust the
prolog of an LLVM function during lowering to clang. Finally we
re-define the RVV segment load/store intrinsics to use the tuple types.

The pull request under the RVV intrinsic specification is
riscv-non-isa/rvv-intrinsic-doc#198

---

This is the 1st patch of the patch-set. This patch is originated from
D98169.

This patch allows aggregate type (StructType) that contains homogeneous
scalable vector types to be a target of load/store/alloca. The RFC of
this patch was posted in LLVM Discourse.

https://discourse.llvm.org/t/rfc-ir-permit-load-store-alloca-for-struct-of-the-same-scalable-vector-type/69527

The main changes in this patch are:

Extend `StructLayout::StructSize` from `uint64_t` to `TypeSize` to
accommodate an expression of scalable size.

Allow `StructType:isSized` to also return true for homogeneous
scalable vector types.

Let `Type::isScalableTy` return true when `Type` is `StructType`
and contains scalable vectors

Extra description is added in the LLVM Language Reference Manual on the
relaxation of this patch.

Authored-by: Hsiangkai Wang <kai.wang@sifive.com>
Co-Authored-by: eop Chen <eop.chen@sifive.com>

Reviewed By: craig.topper, nikic

Differential Revision: https://reviews.llvm.org/D146872

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 504c94f..aec1e34 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4345,8 +4345,10 @@ const SCEV *ScalarEvolution::getOffsetOfExpr(Type *IntTy,
   // We can bypass creating a target-independent constant expression and then
   // folding it back into a ConstantInt. This is just a compile-time
   // optimization.
-  return getConstant(
-      IntTy, getDataLayout().getStructLayout(STy)->getElementOffset(FieldNo));
+  const StructLayout *SL = getDataLayout().getStructLayout(STy);
+  assert(!SL->getSizeInBits().isScalable() &&
+         "Cannot get offset for structure containing scalable vector types");
+  return getConstant(IntTy, SL->getElementOffset(FieldNo));
 }
 
 const SCEV *ScalarEvolution::getUnknown(Value *V) {