[PATCH] D73200: GlobalISel: Add computeKnownBitsForTargetInstr

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: aemerson, aditya_nandakumar, dsanders, paquette.
Herald added subscribers: Petar.Avramovic, volkan, hiraditya, rovka, wdng.
Herald added a project: LLVM.

I think we can save the MRI argument from these since it's in
GISelKnownBits already, but currently not accessible.

Implementation deferred to avoid dependency on other patches.


https://reviews.llvm.org/D73200

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp


Index: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2705,6 +2705,12 @@
   return 1;
 }
 
+unsigned TargetLowering::computeNumSignBitsForTargetInstr(
+  GISelKnownBits &Analysis, Register R, const APInt &DemandedElts,
+  const MachineRegisterInfo &MRI, unsigned Depth) const {
+  return 1;
+}
+
 bool TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
     SDValue Op, const APInt &DemandedElts, APInt &KnownUndef, APInt &KnownZero,
     TargetLoweringOpt &TLO, unsigned Depth) const {
Index: llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -395,6 +395,7 @@
   if (!DstTy.isValid())
     return 1;
 
+  unsigned FirstAnswer = 1;
   switch (Opcode) {
   case TargetOpcode::COPY: {
     MachineOperand &Src = MI.getOperand(1);
@@ -424,13 +425,19 @@
       return NumSrcSignBits - (NumSrcBits - DstTyBits);
     break;
   }
-  default:
+  case TargetOpcode::G_INTRINSIC:
+  case TargetOpcode::G_INTRINSIC_W_SIDE_EFFECTS:
+  default: {
+    unsigned NumBits =
+      TL.computeNumSignBitsForTargetInstr(*this, R, DemandedElts, MRI, Depth);
+    if (NumBits > 1)
+      FirstAnswer = std::max(FirstAnswer, NumBits);
     break;
   }
+  }
 
-  // TODO: Handle target instructions
   // TODO: Fall back to known bits
-  return 1;
+  return FirstAnswer;
 }
 
 unsigned GISelKnownBits::computeNumSignBits(Register R, unsigned Depth) {
Index: llvm/include/llvm/CodeGen/TargetLowering.h
===================================================================
--- llvm/include/llvm/CodeGen/TargetLowering.h
+++ llvm/include/llvm/CodeGen/TargetLowering.h
@@ -3233,6 +3233,16 @@
                                                    const SelectionDAG &DAG,
                                                    unsigned Depth = 0) const;
 
+  /// This method can be implemented by targets that want to expose additional
+  /// information about sign bits to GlobalISel combiners. The DemandedElts
+  /// argument allows us to only collect the minimum sign bits that are shared
+  /// by the requested vector elements.
+  virtual unsigned computeNumSignBitsForTargetInstr(GISelKnownBits &Analysis,
+                                                    Register R,
+                                                    const APInt &DemandedElts,
+                                                    const MachineRegisterInfo &MRI,
+                                                    unsigned Depth = 0) const;
+
   /// Attempt to simplify any target nodes based on the demanded vector
   /// elements, returning true on success. Otherwise, analyze the expression and
   /// return a mask of KnownUndef and KnownZero elements for the expression


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