[PATCH] D136319: [GISel] Rework trunc/shl combine in a generic trunc/shift combine

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

Not sure why you deleted the test



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Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:2262
 
-bool CombinerHelper::matchCombineTruncOfShl(
-    MachineInstr &MI, std::pair<Register, Register> &MatchInfo) {
-  assert(MI.getOpcode() == TargetOpcode::G_TRUNC && "Expected a G_TRUNC");
-  Register DstReg = MI.getOperand(0).getReg();
-  Register SrcReg = MI.getOperand(1).getReg();
-  LLT DstTy = MRI.getType(DstReg);
-  Register ShiftSrc;
-  Register ShiftAmt;
-
-  if (MRI.hasOneNonDBGUse(SrcReg) &&
-      mi_match(SrcReg, MRI, m_GShl(m_Reg(ShiftSrc), m_Reg(ShiftAmt))) &&
-      isLegalOrBeforeLegalizer(
-          {TargetOpcode::G_SHL,
-           {DstTy, getTargetLowering().getPreferredShiftAmountTy(DstTy)}})) {
-    KnownBits Known = KB->getKnownBits(ShiftAmt);
-    unsigned Size = DstTy.getSizeInBits();
-    if (Known.countMaxActiveBits() <= Log2_32(Size)) {
-      MatchInfo = std::make_pair(ShiftSrc, ShiftAmt);
-      return true;
-    }
-  }
-  return false;
+static LLT GetMidVTForTruncRightShiftCombine(LLT ShiftTy, LLT TruncTy) {
+  const unsigned ShiftSize = ShiftTy.getScalarSizeInBits();
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Start with lowercase letter 


================
Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:2313-2316
+    // TODO: Fix truncstore combine to handle (trunc(lshr (trunc x), k)).
+    for (auto &User : MRI.use_instructions(DstReg))
+      if (User.getOpcode() == TargetOpcode::G_STORE)
+        return false;
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I don't understand special casing this, I'd rather just ignore it


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D136319/new/

https://reviews.llvm.org/D136319