[llvm] [CodeGen] Avoid creating instructions dealing with ones if ones aren't involved in the division (PR #99674)

[Craig Topper via llvm-commits]

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@@ -5320,12 +5327,16 @@ MachineInstr *CombinerHelper::buildUDivUsingMul(MachineInstr &MI) {
     Q = MIB.buildAdd(Ty, NPQ, Q).getReg(0);
   }
 
-  Q = MIB.buildLShr(Ty, Q, PostShift).getReg(0);
-  auto One = MIB.buildConstant(Ty, 1);
-  auto IsOne = MIB.buildICmp(
-      CmpInst::Predicate::ICMP_EQ,
-      Ty.isScalar() ? LLT::scalar(1) : Ty.changeElementSize(1), RHS, One);
-  return MIB.buildSelect(Ty, IsOne, LHS, Q);
+  if (hasAOne) {
+    Q = MIB.buildLShr(Ty, Q, PostShift).getReg(0);
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topperc wrote:

If this really removes instructions, you should be able to show that in an MIR test.

https://github.com/llvm/llvm-project/pull/99674