[SVE][CodeGen] Fix up warnings in sve-split-insert/extract tests

I have fixed up some more ElementCount/TypeSize related warnings in
the following tests:

  CodeGen/AArch64/sve-split-extract-elt.ll
  CodeGen/AArch64/sve-split-insert-elt.ll

In SelectionDAG::CreateStackTemporary we were relying upon the implicit
cast from TypeSize -> uint64_t when calling MachineFrameInfo::CreateStackObject.
I've fixed this by passing in the known minimum size instead, which I
believe is fine because the associated stack id indicates whether this
is a scalable object or not.

I've also fixed up a case in TargetLowering::SimplifyDemandedBits when
extracting a vector element from a scalable vector. The result is a scalar,
hence it wasn't caught at the start of the function. If the vector is
scalable we just bail out for now.

Differential Revision: https://reviews.llvm.org/D86431

Author: david-arm

llvm/include/llvm/Support/TypeSize.h

@@ -116,6 +116,15 @@ class ElementCount {
 
   unsigned getKnownMinValue() const { return Min; }
 
+  // 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).
+  unsigned getFixedValue() const {
+    assert(!Scalable &&
+           "Request for a fixed element count on a scalable object");
+    return Min;
+  }
+
   bool isScalable() const { return Scalable; }
 };
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2030,7 +2030,9 @@ SDValue SelectionDAG::CreateStackTemporary(TypeSize Bytes, Align Alignment) {
   int StackID = 0;
   if (Bytes.isScalable())
     StackID = TFI->getStackIDForScalableVectors();
-  int FrameIdx = MFI.CreateStackObject(Bytes, Alignment,
+  // The stack id gives an indication of whether the object is scalable or
+  // not, so it's safe to pass in the minimum size here.
+  int FrameIdx = MFI.CreateStackObject(Bytes.getKnownMinSize(), Alignment,
                                        false, nullptr, StackID);
   return getFrameIndex(FrameIdx, TLI->getFrameIndexTy(getDataLayout()));
 }

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -2022,10 +2022,14 @@ bool TargetLowering::SimplifyDemandedBits(
   case ISD::EXTRACT_VECTOR_ELT: {
     SDValue Src = Op.getOperand(0);
     SDValue Idx = Op.getOperand(1);
-    unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
+    ElementCount SrcEltCnt = Src.getValueType().getVectorElementCount();
     unsigned EltBitWidth = Src.getScalarValueSizeInBits();
 
+    if (SrcEltCnt.isScalable())
+      return false;
+
     // Demand the bits from every vector element without a constant index.
+    unsigned NumSrcElts = SrcEltCnt.getFixedValue();
     APInt DemandedSrcElts = APInt::getAllOnesValue(NumSrcElts);
     if (auto *CIdx = dyn_cast<ConstantSDNode>(Idx))
       if (CIdx->getAPIntValue().ult(NumSrcElts))

llvm/test/CodeGen/AArch64/sve-split-extract-elt.ll

@@ -1,5 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s 2>%t | FileCheck %s
+; RUN: FileCheck --check-prefix=WARN --allow-empty %s <%t
+
+; If this check fails please read test/CodeGen/AArch64/README for instructions on how to resolve it.
+; WARN-NOT: warning
 
 ; EXTRACT VECTOR ELT
 

llvm/test/CodeGen/AArch64/sve-split-insert-elt.ll

@@ -1,5 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s 2>%t | FileCheck %s
+; RUN: FileCheck --check-prefix=WARN --allow-empty %s <%t
+
+; If this check fails please read test/CodeGen/AArch64/README for instructions on how to resolve it.
+; WARN-NOT: warning
 
 ; INSERT VECTOR ELT