[llvm] [AMDGPU] Preserve all analyses if nothing changed (PR #117994)

[Jay Foad via llvm-commits]

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@@ -2303,10 +2303,12 @@ PreservedAnalyses AMDGPUCodeGenPreparePass::run(Function &F,
   SIModeRegisterDefaults Mode(F, *Impl.ST);
   Impl.HasFP32DenormalFlush =
       Mode.FP32Denormals == DenormalMode::getPreserveSign();
+  if (!Impl.run(F))
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jayfoad wrote:

The old code was checking `Impl.FlowChanged` before calling `Impl.run` which seems completely wrong.

https://github.com/llvm/llvm-project/pull/117994