[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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@@ -1174,6 +1174,109 @@ static Instruction *moveAddAfterMinMax(IntrinsicInst *II,
   return IsSigned ? BinaryOperator::CreateNSWAdd(NewMinMax, Add->getOperand(1))
                   : BinaryOperator::CreateNUWAdd(NewMinMax, Add->getOperand(1));
 }
+
+/// Returns weather the it holds for (X LOp Y) ROp Z -> (X ROp Z) LOp (Y ROp Z)
+
+static bool rightDistributesOverLeft(Instruction::BinaryOps ROp, bool HasNUW,
+                                     bool HasNSW, Intrinsic::ID LOp) {
+  switch (LOp) {
+  case Intrinsic::umax:
+    if (HasNUW && (ROp == Instruction::AShr || ROp == Instruction::LShr ||
+                   ROp == Instruction::UDiv || ROp == Instruction::Mul ||
+                   ROp == Instruction::Add))
+      return true;
+    return false;
+  case Intrinsic::umin:
+    if (HasNUW && (ROp == Instruction::AShr || ROp == Instruction::LShr ||
+                   ROp == Instruction::UDiv || ROp == Instruction::Sub))
+      return true;
+    return false;
+  case Intrinsic::smax:
+  case Intrinsic::smin:
+    if (HasNSW && ROp == Instruction::AShr)
+      return true;
+    return false;
+  default:
+    return false;
+  }
+}
+
+///  Try canonicalize max(max(X,C1) binop C2, C3) -> max(X binop C2, max(C1
+///  binop C2, C3))
+/// -> max(X binop C2, C4)  //
+
+static Instruction *reduceMinMax(IntrinsicInst *II,
+                                 InstCombiner::BuilderTy &Builder,
+                                 const DataLayout &DL) {
+  Intrinsic::ID MinMaxID = II->getIntrinsicID();
+  assert(isa<MinMaxIntrinsic>(II) && "Expected a min or max intrinsic");
+
+  Value *Op0 = II->getArgOperand(0), *Op1 = II->getArgOperand(1);
+  Value *InnerMax;
+  Constant *C2, *C3;
+  if (!match(Op0, m_OneUse(m_BinOp(m_Value(InnerMax), m_ImmConstant(C2)))) ||
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dtcxzyw wrote:

Please add some multi-use tests. See also https://llvm.org/docs/InstCombineContributorGuide.html#add-multi-use-tests.

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