[RISCV][GISel] Falling back to SDISel for scalable vector type values (#70133)

This patch also tests the fallback of unsupported formal arguments.

Author: mshockwave

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -19304,6 +19304,23 @@ unsigned RISCVTargetLowering::getCustomCtpopCost(EVT VT,
   return isCtpopFast(VT) ? 0 : 1;
 }
 
+bool RISCVTargetLowering::fallBackToDAGISel(const Instruction &Inst) const {
+  // We don't support scalable vectors in GISel.
+  if (Inst.getType()->isScalableTy())
+    return true;
+
+  for (unsigned i = 0; i < Inst.getNumOperands(); ++i)
+    if (Inst.getOperand(i)->getType()->isScalableTy())
+      return true;
+
+  if (const AllocaInst *AI = dyn_cast<AllocaInst>(&Inst)) {
+    if (AI->getAllocatedType()->isScalableTy())
+      return true;
+  }
+
+  return false;
+}
+
 namespace llvm::RISCVVIntrinsicsTable {
 
 #define GET_RISCVVIntrinsicsTable_IMPL

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -800,6 +800,8 @@ class RISCVTargetLowering : public TargetLowering {
 
   unsigned getMaxSupportedInterleaveFactor() const override { return 8; }
 
+  bool fallBackToDAGISel(const Instruction &Inst) const override;
+
   bool lowerInterleavedLoad(LoadInst *LI,
                             ArrayRef<ShuffleVectorInst *> Shuffles,
                             ArrayRef<unsigned> Indices,

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/fallback.ll

@@ -0,0 +1,44 @@
+; RUN: llc -mtriple=riscv64 -mattr='+v' -O0 -global-isel -global-isel-abort=2 -pass-remarks-missed='gisel*' -verify-machineinstrs %s -o %t.out 2> %t.err
+; RUN: FileCheck %s --check-prefix=FALLBACK-WITH-REPORT-OUT < %t.out
+; RUN: FileCheck %s --check-prefix=FALLBACK-WITH-REPORT-ERR < %t.err
+
+
+declare <vscale x 1 x i8> @llvm.riscv.vadd.nxv1i8.nxv1i8(
+  <vscale x 1 x i8>,
+  <vscale x 1 x i8>,
+  <vscale x 1 x i8>,
+  i64)
+
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to lower arguments{{.*}}scalable_arg
+; FALLBACK-WITH-REPORT-OUT-LABEL: scalable_arg
+define <vscale x 1 x i8> @scalable_arg(<vscale x 1 x i8> %0, <vscale x 1 x i8> %1, i64 %2) nounwind {
+entry:
+  %a = call <vscale x 1 x i8> @llvm.riscv.vadd.nxv1i8.nxv1i8(
+    <vscale x 1 x i8> undef,
+    <vscale x 1 x i8> %0,
+    <vscale x 1 x i8> %1,
+    i64 %2)
+
+  ret <vscale x 1 x i8> %a
+}
+
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to translate instruction{{.*}}scalable_inst
+; FALLBACK-WITH-REPORT-OUT-LABEL: scalable_inst
+define <vscale x 1 x i8> @scalable_inst(i64 %0) nounwind {
+entry:
+  %a = call <vscale x 1 x i8> @llvm.riscv.vadd.nxv1i8.nxv1i8(
+    <vscale x 1 x i8> undef,
+    <vscale x 1 x i8> undef,
+    <vscale x 1 x i8> undef,
+    i64 %0)
+
+  ret <vscale x 1 x i8> %a
+}
+
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to translate instruction{{.*}}scalable_alloca
+; FALLBACK-WITH-REPORT-OUT-LABEL: scalable_alloca
+define void @scalable_alloca() #1 {
+  %local0 = alloca <vscale x 16 x i8>
+  load volatile <vscale x 16 x i8>, ptr %local0
+  ret void
+}