[llvm] [InstCombine] Fold max(max(x, c1) << c2, c3) —> max(x << c2, c3) when c3 >= c1 * 2 ^ c2 (PR #140526)

[Yingwei Zheng via llvm-commits]

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@@ -1171,6 +1171,84 @@ static Instruction *moveAddAfterMinMax(IntrinsicInst *II,
   return IsSigned ? BinaryOperator::CreateNSWAdd(NewMinMax, Add->getOperand(1))
                   : BinaryOperator::CreateNUWAdd(NewMinMax, Add->getOperand(1));
 }
+
+//Try canonicalize min/max(x << shamt, c<<shamt) into max(x, c) << shamt
+static Instruction *moveShiftAfterMinMax(IntrinsicInst *II, InstCombiner::BuilderTy &Builder) {
+  Intrinsic::ID MinMaxID = II->getIntrinsicID();
+  assert((MinMaxID == Intrinsic::smax || MinMaxID == Intrinsic::smin ||
+    MinMaxID == Intrinsic::umax || MinMaxID == Intrinsic::umin) &&
+   "Expected a min or max intrinsic");
+  
+  Value *Op0 = II->getArgOperand(0), *Op1 = II->getArgOperand(1);
+  Value *InnerMax;
+  const APInt *C;
+  if (!match(Op0, m_OneUse(m_BinOp(m_Value(InnerMax), m_APInt(C)))) || 
+      !match(Op1, m_APInt(C)))
+      return nullptr;
+  
+  auto* BinOpInst = cast<BinaryOperator>(Op0);
+  Instruction::BinaryOps BinOp = BinOpInst->getOpcode();
+  Value *X;
+  InnerMax = BinOpInst->getOperand(0);
+  // std::cout<< InnerMax->dump() <<std::endl;
+  if(!match(InnerMax,m_OneUse(m_Intrinsic<Intrinsic::umax>(m_Value(X),m_APInt(C))))){
+  if(!match(InnerMax,m_OneUse(m_Intrinsic<Intrinsic::smax>(m_Value(X),m_APInt(C))))){
+  if(!match(InnerMax,m_OneUse(m_Intrinsic<Intrinsic::umin>(m_Value(X),m_APInt(C))))){
+  if(!match(InnerMax,m_OneUse(m_Intrinsic<Intrinsic::smin>(m_Value(X),m_APInt(C))))){
+     return nullptr;
+  }}}}
+  
+  auto *InnerMaxInst = cast<IntrinsicInst>(InnerMax);
+
+  bool IsSigned = MinMaxID == Intrinsic::smax || MinMaxID == Intrinsic::smin;
+  if((IsSigned && !BinOpInst->hasNoSignedWrap()) ||
+     (!IsSigned && !BinOpInst->hasNoUnsignedWrap())) 
+     return nullptr;
+
----------------
dtcxzyw wrote:

Should check that inner min/max has the same intrinsic ID as the outer one.


https://github.com/llvm/llvm-project/pull/140526