[AVX-512] Add support for commuting VPTERNLOG instructions.

VPTERNLOG is a ternary instruction with an immediate specifying the logical operation to perform. For each bit position in the 3 source vectors the bit from each source is concatenated together and the resulting 3-bit value is used to select a bit in the immediate. This bit value is written to the result vector.

We can commute this by swapping operands and modifying the immediate. To modify the immediate we need to swap two pairs of bits. The pairs correspond to the locations in the immediate where the commuted operands bits have opposite values and the uncommuted operand has the same value. Bits 0 and 7 will never be swapped since the relevant bits from all sources are the same value.

This refactors and reuses parts of the FMA3 commuting code which is also a three operand instruction.

llvm-svn: 282132

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index a891af566d8..f5c7c3855fc 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -586,6 +586,25 @@ private:
   /// operand and follow operands form a reference to the stack frame.
   bool isFrameOperand(const MachineInstr &MI, unsigned int Op,
                       int &FrameIndex) const;
+
+  /// Returns true iff the routine could find two commutable operands in the
+  /// given machine instruction with 3 vector inputs.
+  /// The 'SrcOpIdx1' and 'SrcOpIdx2' are INPUT and OUTPUT arguments. Their
+  /// input values can be re-defined in this method only if the input values
+  /// are not pre-defined, which is designated by the special value
+  /// 'CommuteAnyOperandIndex' assigned to it.
+  /// If both of indices are pre-defined and refer to some operands, then the
+  /// method simply returns true if the corresponding operands are commutable
+  /// and returns false otherwise.
+  ///
+  /// For example, calling this method this way:
+  ///     unsigned Op1 = 1, Op2 = CommuteAnyOperandIndex;
+  ///     findThreeSrcCommutedOpIndices(MI, Op1, Op2);
+  /// can be interpreted as a query asking to find an operand that would be
+  /// commutable with the operand#1.
+  bool findThreeSrcCommutedOpIndices(const MachineInstr &MI,
+                                     unsigned &SrcOpIdx1,
+                                     unsigned &SrcOpIdx2) const;
 };
 
 } // End llvm namespace