[llvm] [GlobalISel] Handle div-by-pow2 (PR #83155)

[Shilei Tian via llvm-commits]

================
@@ -5286,6 +5286,62 @@ MachineInstr *CombinerHelper::buildSDivUsingMul(MachineInstr &MI) {
   return MIB.buildMul(Ty, Res, Factor);
 }
 
+bool CombinerHelper::matchSDivByPow2(MachineInstr &MI) {
+  assert(MI.getOpcode() == TargetOpcode::G_SDIV && "Expected SDIV");
+  auto &SDiv = cast<GenericMachineInstr>(MI);
+  Register RHS = SDiv.getReg(2);
+  auto MatchPow2 = [&](const Constant *C) {
+    if (auto *CI = dyn_cast<ConstantInt>(C))
+      return CI->getValue().isPowerOf2() || CI->getValue().isNegatedPowerOf2();
+    return false;
+  };
+  return matchUnaryPredicate(MRI, RHS, MatchPow2, /* AllowUndefs */ false);
+}
+
+void CombinerHelper::applySDivByPow2(MachineInstr &MI) {
----------------
shiltian wrote:

This function is basically a 1:1 mapping from the SelectionDAG version.

https://github.com/llvm/llvm-project/pull/83155