[llvm] [LLVM][CodeGen] Teach SelectionDAG how to expand FREM to a vector math call. (PR #83859)

[Paul Walker via llvm-commits]

================
@@ -1842,6 +1859,116 @@ void VectorLegalizer::ExpandREM(SDNode *Node,
   Results.push_back(Result);
 }
 
+// Try to expand libm nodes into a call to a vector math. Callers provide the
+// LibFunc equivalent of the passed in Node, which is used to lookup mappings
+// within TargetLibraryInfo. Only simply mappings are considered whereby only
+// matching vector operands are allowed and masked functions are passed an all
+// true vector (i.e. Node cannot be a predicated operation).
+bool VectorLegalizer::tryExpandVecMathCall(SDNode *Node, RTLIB::Libcall LC,
+                                           SmallVectorImpl<SDValue> &Results) {
+  // Chain must be propagated but currently strict fp operations are down
+  // converted to their none strict counterpart.
+  assert(!Node->isStrictFPOpcode() && "Unexpected strict fp operation!");
+
+  const char *LCName = TLI.getLibcallName(LC);
+  if (!LCName)
+    return false;
+  LLVM_DEBUG(dbgs() << "Looking for vector variant of " << LCName << "\n");
+
+  EVT VT = Node->getValueType(0);
+  ElementCount VL = VT.getVectorElementCount();
+
+  // Lookup a vector function equivalent to the specified libcall. Prefer
+  // unmasked variants but we will generate a mask if need be.
+  const TargetLibraryInfo &TLibInfo = DAG.getLibInfo();
+  const VecDesc *VD = TLibInfo.getVectorMappingInfo(LCName, VL, false);
+  if (!VD)
+    VD = TLibInfo.getVectorMappingInfo(LCName, VL, /*Masked*/ true);
+  if (!VD)
+    return false;
+
+  LLVMContext *Ctx = DAG.getContext();
+  Type *Ty = VT.getTypeForEVT(*Ctx);
+  Type *ScalarTy = Ty->getScalarType();
+
+  // Construct a scalar function type based on Node's operands.
+  SmallVector<Type *, 8> ArgTys;
+  for (unsigned i = 0; i < Node->getNumOperands(); ++i) {
+    assert(Node->getOperand(i).getValueType() == VT &&
+           "Expected matching vector types!");
+    ArgTys.push_back(ScalarTy);
+  }
+  FunctionType *ScalarFTy = FunctionType::get(ScalarTy, ArgTys, false);
+
+  // Generate call information for the vector function.
+  const std::string MangledName = VD->getVectorFunctionABIVariantString();
+  auto OptVFInfo = VFABI::tryDemangleForVFABI(MangledName, ScalarFTy);
+  if (!OptVFInfo)
+    return false;
+
+  LLVM_DEBUG(dbgs() << "Found vector variant " << VD->getVectorFnName()
+                    << "\n");
+
+  // Sanity check just in case OptVFInfo has unexpected paramaters.
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paulwalker-arm wrote:

Done.

https://github.com/llvm/llvm-project/pull/83859