[llvm] [RISCV] Allow non-loop invariant steps in RISCVGatherScatterLowering (PR #122244)

[Craig Topper via llvm-commits]

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@@ -310,18 +307,31 @@ bool RISCVGatherScatterLowering::matchStridedRecurrence(Value *Index, Loop *L,
   }
   case Instruction::Mul: {
     Start = Builder.CreateMul(Start, SplatOp, "start");
-    Step = Builder.CreateMul(Step, SplatOp, "step");
     Stride = Builder.CreateMul(Stride, SplatOp, "stride");
     break;
   }
   case Instruction::Shl: {
     Start = Builder.CreateShl(Start, SplatOp, "start");
-    Step = Builder.CreateShl(Step, SplatOp, "step");
     Stride = Builder.CreateShl(Stride, SplatOp, "stride");
     break;
   }
   }
 
+  // Adjust the step value after its definition if it's an instruction.
+  if (auto *StepI = dyn_cast<Instruction>(Step))
+    Builder.SetInsertPoint(*StepI->getInsertionPointAfterDef());
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topperc wrote:

If the Step is a loop invariant in an earlier basic block, does this put the new step farther away then necessary. Should we only do this if the Step instruction is in the loop?

https://github.com/llvm/llvm-project/pull/122244