[llvm] [LSR] Recognize vscale-relative immediates (PR #88124)

[Graham Hunter via llvm-commits]

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@@ -3931,21 +4082,26 @@ void LSRInstance::GenerateConstantOffsetsImpl(
         int64_t Step = StepInt.isNegative() ?
           StepInt.getSExtValue() : StepInt.getZExtValue();
 
-        for (int64_t Offset : Worklist) {
-          Offset -= Step;
-          GenerateOffset(G, Offset);
+        for (Immediate Offset : Worklist) {
+          if (!Offset.isScalable()) {
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huntergr-arm wrote:

It's trying to subtract an APInt derived from a fixed SCEVAddRecExpr step. We may be able to check for a scalable step to make use of this, but I'd want to come up with an appropriate test first.

https://github.com/llvm/llvm-project/pull/88124