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

[Graham Hunter via llvm-commits]

================
@@ -1401,24 +1483,29 @@ void Cost::RateFormula(const Formula &F,
     // allows to fold 2 registers.
     C.NumBaseAdds +=
         NumBaseParts - (1 + (F.Scale && isAMCompletelyFolded(*TTI, LU, F)));
-  C.NumBaseAdds += (F.UnfoldedOffset != 0);
+  C.NumBaseAdds += (F.UnfoldedOffset.isNonZero());
 
   // Accumulate non-free scaling amounts.
   C.ScaleCost += *getScalingFactorCost(*TTI, LU, F, *L).getValue();
 
   // Tally up the non-zero immediates.
   for (const LSRFixup &Fixup : LU.Fixups) {
-    int64_t O = Fixup.Offset;
-    int64_t Offset = (uint64_t)O + F.BaseOffset;
+    // FIXME: We probably want to noticeably increase the cost if the
+    // two offsets differ in scalability?
+    bool Scalable = Fixup.Offset.isScalable() || F.BaseOffset.isScalable();
+    int64_t O = Fixup.Offset.getKnownMinValue();
+    Immediate Offset = Immediate::get(
+        (uint64_t)(O) + F.BaseOffset.getKnownMinValue(), Scalable);
----------------
huntergr-arm wrote:

I think it's more that a wrapper for the casted arithmetic is needed. Right now we would need to cast and add the scalable and fixed parts of StackOffset independently.

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