[PATCH] D40320: [NFC] CodeGen: Handle shift amount type in DAGTypeLegalizer::SplitInteger

[Yaxun Liu via Phabricator via llvm-commits]

yaxunl created this revision.

This patch reverts change to X86TargetLowering::getScalarShiftAmountTy in
https://reviews.llvm.org/rL318727 and move the logic to DAGTypeLegalizer::SplitInteger.

The reason is that getScalarShiftAmountTy returns a shift amount type that
is suitable for common use cases in CodeGen. DAGTypeLegalizer::SplitInteger
is a rare situation which requires a shift amount type larger than what
getScalarShiftAmountTy. In this case, it is more reasonable to do special
handling of shift amount type in DAGTypeLegalizer::SplitInteger only. If
similar situations arises the logic may be moved to a separate function.

Since this is NFC, existing lit tests are sufficient.


https://reviews.llvm.org/D40320

Files:
  lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
  lib/Target/X86/X86ISelLowering.h


Index: lib/Target/X86/X86ISelLowering.h
===================================================================
--- lib/Target/X86/X86ISelLowering.h
+++ lib/Target/X86/X86ISelLowering.h
@@ -18,7 +18,6 @@
 #include "llvm/CodeGen/CallingConvLower.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/TargetLowering.h"
-#include "llvm/Support/MathExtras.h"
 #include "llvm/Target/TargetOptions.h"
 
 namespace llvm {
@@ -665,14 +664,8 @@
     void markLibCallAttributes(MachineFunction *MF, unsigned CC,
                                ArgListTy &Args) const override;
 
-    // For i512, DAGTypeLegalizer::SplitInteger needs a shift amount 256,
-    // which cannot be held by i8, therefore use i16 instead. In all the
-    // other situations i8 is sufficient.
     MVT getScalarShiftAmountTy(const DataLayout &, EVT VT) const override {
-      MVT T = VT.getSizeInBits() >= 512 ? MVT::i16 : MVT::i8;
-      assert((VT.getSizeInBits() + 1) / 2 < (1U << T.getSizeInBits()) &&
-             "Scalar shift amount type too small");
-      return T;
+      return MVT::i8;
     }
 
     const MCExpr *
Index: lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
+++ lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
@@ -1172,11 +1172,13 @@
   assert(LoVT.getSizeInBits() + HiVT.getSizeInBits() ==
          Op.getValueSizeInBits() && "Invalid integer splitting!");
   Lo = DAG.getNode(ISD::TRUNCATE, dl, LoVT, Op);
-  Hi =
-      DAG.getNode(ISD::SRL, dl, Op.getValueType(), Op,
-                  DAG.getConstant(LoVT.getSizeInBits(), dl,
-                                  TLI.getScalarShiftAmountTy(
-                                      DAG.getDataLayout(), Op.getValueType())));
+  unsigned ReqShiftAmountInBits = Log2_32(LoVT.getSizeInBits()) + 1;
+  MVT ShiftAmountTy =
+      TLI.getScalarShiftAmountTy(DAG.getDataLayout(), Op.getValueType());
+  if (ReqShiftAmountInBits > ShiftAmountTy.getSizeInBits())
+    ShiftAmountTy = MVT::getIntegerVT(NextPowerOf2(ReqShiftAmountInBits));
+  Hi = DAG.getNode(ISD::SRL, dl, Op.getValueType(), Op,
+                   DAG.getConstant(LoVT.getSizeInBits(), dl, ShiftAmountTy));
   Hi = DAG.getNode(ISD::TRUNCATE, dl, HiVT, Hi);
 }
 


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