[llvm] [X86] Remove TuningPOPCNTFalseDeps from AlderLake (PR #154004)

[via llvm-commits]

ms178 wrote:

Could you please take a look if that is also true for TuningLZCNTFalseDeps? I've applied the patch below locally which also implements  [FeatureERMSB, FeatureFSRM] for Raptor Lake and it seems to perform fine, but that might be an idea for another patch.

```
--- a/llvm/lib/Target/X86/X86.td	2025-08-17 08:57:51.604276317 +0200
+++ b/llvm/lib/Target/X86/X86.td	2025-08-17 09:07:22.804296154 +0200
@@ -1291,10 +1292,23 @@ def ProcessorFeatures {
   list<SubtargetFeature> ADLAdditionalTuning = [TuningPERMFalseDeps,
                                                 TuningPreferMovmskOverVTest,
                                                 TuningFastImmVectorShift];
-  list<SubtargetFeature> ADLTuning = !listconcat(SKLTuning, ADLAdditionalTuning);
+  // Remove inherited false-dependency tunings that do not apply on Alder/Raptor Lake
+  list<SubtargetFeature> ADLRemoveTuning = [TuningPOPCNTFalseDeps,
+                                            TuningLZCNTFalseDeps];
+  list<SubtargetFeature> ADLTuning =
+    !listremove(!listconcat(SKLTuning, ADLAdditionalTuning), ADLRemoveTuning);
   list<SubtargetFeature> ADLFeatures =
     !listconcat(TRMFeatures, ADLAdditionalFeatures);
 
+  // Raptor Lake (client, no AVX-512): enable fast string ops + prefer 128-bit compute
+  list<SubtargetFeature> RLAdditionalFeatures = [FeatureERMSB, FeatureFSRM];
+  list<SubtargetFeature> RLFeatures =
+    !listconcat(ADLFeatures, RLAdditionalFeatures);
+
+  list<SubtargetFeature> RLAdditionalTuning = [TuningPrefer128Bit];
+  list<SubtargetFeature> RLTuning =
+    !listconcat(ADLTuning, RLAdditionalTuning);
+
   // Gracemont
   list<SubtargetFeature> GRTTuning = [TuningMacroFusion,
                                       TuningSlow3OpsLEA,
@@ -1866,7 +1880,7 @@ foreach P = ["sierraforest", "grandridge
                 ProcessorFeatures.GRTTuning>;
 }
 def : ProcModel<"raptorlake", AlderlakePModel,
-                ProcessorFeatures.ADLFeatures, ProcessorFeatures.ADLTuning>;
+                ProcessorFeatures.RLFeatures, ProcessorFeatures.RLTuning>;
 def : ProcModel<"meteorlake", AlderlakePModel,
                 ProcessorFeatures.ADLFeatures, ProcessorFeatures.ADLTuning>;
 def : ProcModel<"arrowlake", AlderlakePModel,

```

https://github.com/llvm/llvm-project/pull/154004