[PATCH] D71883: [PowerPC] Use PredictableSelectIsExpensive to enable select to branch in CGP

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang updated this revision to Diff 236523.
ZhangKang marked 2 inline comments as done.
ZhangKang added a comment.

Modified the patch to follow Nemanjai's comments.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71883/new/

https://reviews.llvm.org/D71883

Files:
  llvm/lib/Target/PowerPC/PPC.td
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/lib/Target/PowerPC/PPCSubtarget.cpp
  llvm/lib/Target/PowerPC/PPCSubtarget.h


Index: llvm/lib/Target/PowerPC/PPCSubtarget.h
===================================================================
--- llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -140,6 +140,7 @@
   bool VectorsUseTwoUnits;
   bool UsePPCPreRASchedStrategy;
   bool UsePPCPostRASchedStrategy;
+  bool PredictableSelectIsExpensive;
 
   POPCNTDKind HasPOPCNTD;
 
@@ -389,6 +390,10 @@
   }
 
   bool isXRaySupported() const override { return IsPPC64 && IsLittleEndian; }
+
+  bool isPredictableSelectIsExpensive() const {
+    return PredictableSelectIsExpensive;
+  }
 };
 } // End llvm namespace
 
Index: llvm/lib/Target/PowerPC/PPCSubtarget.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCSubtarget.cpp
+++ llvm/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -116,6 +116,7 @@
   VectorsUseTwoUnits = false;
   UsePPCPreRASchedStrategy = false;
   UsePPCPostRASchedStrategy = false;
+  PredictableSelectIsExpensive = false;
 
   HasPOPCNTD = POPCNTD_Unavailable;
 }
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1280,6 +1280,11 @@
     MaxLoadsPerMemcmp = 8;
     MaxLoadsPerMemcmpOptSize = 4;
   }
+
+  // Let the subtarget (CPU) decide if a predictable select is more expensive
+  // than the corresponding branch. This information is used in CGP to decide
+  // when to convert selects into branches.
+  PredictableSelectIsExpensive = Subtarget.isPredictableSelectIsExpensive();
 }
 
 /// getMaxByValAlign - Helper for getByValTypeAlignment to determine
Index: llvm/lib/Target/PowerPC/PPC.td
===================================================================
--- llvm/lib/Target/PowerPC/PPC.td
+++ llvm/lib/Target/PowerPC/PPC.td
@@ -210,6 +210,13 @@
                                                  "true",
                                                  "Vectors use two units">;
 
+
+def FeaturePredictableSelectIsExpensive :
+  SubtargetFeature<"predictable-select-expensive",
+                   "PredictableSelectIsExpensive",
+                   "true",
+                   "Prefer likely predicted branches over selects">;
+
 // Since new processors generally contain a superset of features of those that
 // came before them, the idea is to make implementations of new processors
 // less error prone and easier to read.
@@ -277,10 +284,14 @@
     !listconcat(P8InheritableFeatures, P8SpecificFeatures);
 
   // Power9
-  list<SubtargetFeature> P9AdditionalFeatures = [DirectivePwr9,
-                                                 FeatureP9Altivec,
-                                                 FeatureP9Vector,
-                                                 FeatureISA3_0];
+  list<SubtargetFeature> P9AdditionalFeatures =
+    [DirectivePwr9,
+     FeatureP9Altivec,
+     FeatureP9Vector,
+     FeatureISA3_0,
+     FeaturePredictableSelectIsExpensive
+     ];
+
   // Some features are unique to Power9 and there is no reason to assume
   // they will be part of any future CPUs. One example is the narrower
   // dispatch for vector operations than scalar ones. For the time being,


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