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

[Philip Reames 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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preames wrote:

Good catch in both respects.  We need to insert this at the end of the preheader if Step is outside the loop.  

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