[llvm] [TTI] getScalingFactorCost should return InstructionCost::getInvalid() instead of -1. (PR #129802)

[David Sherwood via llvm-commits]

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@@ -364,7 +364,7 @@ class TargetTransformInfoImplBase {
                               Scale, AddrSpace, /*I=*/nullptr,
                               BaseOffset.getScalable()))
       return 0;
-    return -1;
+    return InstructionCost::getInvalid();
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david-arm wrote:

The fix looks sensible, but the fact all the tests pass means that we were also missing some test coverage. Do you know if it's even possible to expose the invalid cost path in a test?

https://github.com/llvm/llvm-project/pull/129802