[PATCH] D143786: [X86] Add `TuningPreferShiftShuffle` for when Shifts are preferable to shuffles.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:16572
 
+
     // Try to use bit rotation instructions.
----------------
remove newline


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:38819
     }
-  }
-
-  // Attempt to match against byte/bit shifts.
-  if (AllowIntDomain &&
-      ((MaskVT.is128BitVector() && Subtarget.hasSSE2()) ||
-       (MaskVT.is256BitVector() && Subtarget.hasAVX2()) ||
-       (MaskVT.is512BitVector() && Subtarget.hasAVX512()))) {
-    int ShiftAmt = matchShuffleAsShift(ShuffleVT, Shuffle, MaskScalarSizeInBits,
-                                       Mask, 0, Zeroable, Subtarget);
-    if (0 < ShiftAmt && (!ShuffleVT.is512BitVector() || Subtarget.hasBWI() ||
-                         32 <= ShuffleVT.getScalarSizeInBits())) {
-      PermuteImm = (unsigned)ShiftAmt;
-      return true;
-    }
-  }
-
-  // Attempt to match against bit rotates.
-  if (!ContainsZeros && AllowIntDomain && MaskScalarSizeInBits < 64 &&
-      ((MaskVT.is128BitVector() && Subtarget.hasXOP()) ||
-       Subtarget.hasAVX512())) {
-    int RotateAmt = matchShuffleAsBitRotate(ShuffleVT, MaskScalarSizeInBits,
-                                            Subtarget, Mask);
-    if (0 < RotateAmt) {
-      Shuffle = X86ISD::VROTLI;
-      PermuteImm = (unsigned)RotateAmt;
-      return true;
+    // Attempt to match against byte/bit shifts.
+    if (AllowIntDomain &&
----------------
newline


================
Comment at: llvm/lib/Target/X86/X86Subtarget.h:252
 
+  bool hasFasterShiftThanShuffle() const { return PreferLowerShuffleAsShift; }
   // If there are no 512-bit vectors and we prefer not to use 512-bit registers,
----------------
You shouldn't need this - the GET_SUBTARGETINFO_MACRO above should have created the getter


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D143786/new/

https://reviews.llvm.org/D143786