[SVE][CodeGen] Fix implicit TypeSize->uint64_t conversion in TransformFPLoadStorePair

[david-arm]

Summary

In DAGCombiner::TransformFPLoadStorePair we were dropping the scalable
property of TypeSize when trying to create an integer type of equivalent
size. In fact, this optimisation makes no sense for scalable types
since we don't know the size at compile time. I have changed the code
to bail out when encountering scalable type sizes.

I've added a test to

llvm/test/CodeGen/AArch64/sve-fp.ll

that exercises this code path. The test already emits an error if it
encounters warnings due to implicit TypeSize->uint64_t conversions.

[efriedma]

LGTM

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

15760

Mixing early return and non-early-return like this is confusing. But I guess also orthogonal.

15763

The isFloatingPoint check here seems weird; it doesn't really make sense to handle float vectors, but not int vectors. But I guess that's orthogonal.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

 
 /// For a given floating point load / store pair, if the load value isn't used
 /// by any other operations, then consider transforming the pair to integer
 /// load / store operations if the target deems the transformation profitable.
 SDValue DAGCombiner::TransformFPLoadStorePair(SDNode *N) {
   StoreSDNode *ST  = cast<StoreSDNode>(N);
   SDValue Value = ST->getValue();
   if (ISD::isNormalStore(ST) && ISD::isNormalLoad(Value.getNode()) &&
       Value.hasOneUse()) {
     LoadSDNode *LD = cast<LoadSDNode>(Value);
     EVT VT = LD->getMemoryVT();
     if (!VT.isFloatingPoint() ||
         VT != ST->getMemoryVT() ||
         LD->isNonTemporal() ||
         ST->isNonTemporal() ||
         LD->getPointerInfo().getAddrSpace() != 0 ||
         ST->getPointerInfo().getAddrSpace() != 0)
       return SDValue();
 
-    EVT IntVT = EVT::getIntegerVT(*DAG.getContext(), VT.getSizeInBits());
+    TypeSize VTSize = VT.getSizeInBits();
+
+    // We don't know the size of scalable types at compile time so we cannot
+    // create an integer of the equivalent size.
+    if (VTSize.isScalable())
+      return SDValue();
+
+    EVT IntVT = EVT::getIntegerVT(*DAG.getContext(), VTSize.getFixedSize());
     if (!TLI.isOperationLegal(ISD::LOAD, IntVT) ||
         !TLI.isOperationLegal(ISD::STORE, IntVT) ||
         !TLI.isDesirableToTransformToIntegerOp(ISD::LOAD, VT) ||
         !TLI.isDesirableToTransformToIntegerOp(ISD::STORE, VT))
       return SDValue();
 
     Align LDAlign = LD->getAlign();
     Align STAlign = ST->getAlign();

llvm/test/CodeGen/AArch64/sve-fp.ll

; CHECK-NEXT:    ret
   %imagp = getelementptr inbounds %complex, %complex* %outval, i64 0, i32 0, i32 1
   %1 = call double @llvm.aarch64.sve.faddv.nxv2f64(<vscale x 2 x i1> %pred, <vscale x 2 x double> %in1)
   %2 = call double @llvm.aarch64.sve.faddv.nxv2f64(<vscale x 2 x i1> %pred, <vscale x 2 x double> %in2)
   store double %1, double* %realp, align 8
   store double %2, double* %imagp, align 8
   ret void
 }
 
+define void @float_copy(<vscale x 4 x float>* %P1, <vscale x 4 x float>* %P2) {
+; CHECK-LABEL: float_copy:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.s
+; CHECK-NEXT:    ld1w { z0.s }, p0/z, [x0]
+; CHECK-NEXT:    st1w { z0.s }, p0, [x1]
+; CHECK-NEXT:    ret
+  %A = load <vscale x 4 x float>, <vscale x 4 x float>* %P1, align 16
+  store <vscale x 4 x float> %A, <vscale x 4 x float>* %P2, align 16
+  ret void
+}
+
 declare <vscale x 8 x half> @llvm.aarch64.sve.frecps.x.nxv8f16(<vscale x 8 x half>, <vscale x 8 x half>)
 declare <vscale x 4 x float>  @llvm.aarch64.sve.frecps.x.nxv4f32(<vscale x 4 x float> , <vscale x 4 x float>)
 declare <vscale x 2 x double> @llvm.aarch64.sve.frecps.x.nxv2f64(<vscale x 2 x double>, <vscale x 2 x double>)
 
 declare <vscale x 8 x half> @llvm.aarch64.sve.frsqrts.x.nxv8f16(<vscale x 8 x half>, <vscale x 8 x half>)
 declare <vscale x 4 x float> @llvm.aarch64.sve.frsqrts.x.nxv4f32(<vscale x 4 x float>, <vscale x 4 x float>)
 declare <vscale x 2 x double> @llvm.aarch64.sve.frsqrts.x.nxv2f64(<vscale x 2 x double>, <vscale x 2 x double>)
 
 declare <vscale x 2 x double> @llvm.fma.nxv2f64(<vscale x 2 x double>, <vscale x 2 x double>, <vscale x 2 x double>)
 declare <vscale x 4 x float> @llvm.fma.nxv4f32(<vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>)
 declare <vscale x 8 x half> @llvm.fma.nxv8f16(<vscale x 8 x half>, <vscale x 8 x half>, <vscale x 8 x half>)
 
 ; Function Attrs: nounwind readnone
 declare double @llvm.aarch64.sve.faddv.nxv2f64(<vscale x 2 x i1>, <vscale x 2 x double>) #2