[PowerPC] add a new subtarget feature fastMFLR

Some PowerPC CPU may have slow MFLR instruction, so we need to
schedule the MFLR and its store in function prologue away to
hidden the long latency for slow MFLR instruction.

This patch adds a new feature fastMFLR and the new feature will
be used in https://reviews.llvm.org/D137423.

Reviewed By: RolandF

Differential Revision: https://reviews.llvm.org/D137612

diff --git a/llvm/lib/Target/PowerPC/PPC.td b/llvm/lib/Target/PowerPC/PPC.td
index c231bb4..53f930b 100644 (file)
--- a/llvm/lib/Target/PowerPC/PPC.td
+++ b/llvm/lib/Target/PowerPC/PPC.td
@@ -316,6 +316,9 @@ def FeaturePredictableSelectIsExpensive :
                    "true",
                    "Prefer likely predicted branches over selects">;
 
+def FeatureFastMFLR : SubtargetFeature<"fast-MFLR", "HasFastMFLR", "true",
+                                       "MFLR is a fast instruction">;
+
 // 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.
@@ -424,7 +427,7 @@ def ProcessorFeatures {
     !listconcat(FusionFeatures, [
        DirectivePwr10, FeatureISA3_1, FeaturePrefixInstrs,
        FeaturePCRelativeMemops, FeatureP10Vector, FeatureMMA,
-       FeaturePairedVectorMemops]);
+       FeaturePairedVectorMemops, FeatureFastMFLR]);
   list<SubtargetFeature> P10SpecificFeatures = [];
   list<SubtargetFeature> P10InheritableFeatures =
     !listconcat(P9InheritableFeatures, P10AdditionalFeatures);

diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
index 9842423..599629c 100644 (file)
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -149,6 +149,7 @@ void PPCSubtarget::initializeEnvironment() {
   UsePPCPostRASchedStrategy = false;
   PairedVectorMemops = false;
   PredictableSelectIsExpensive = false;
+  HasFastMFLR = false;
   HasModernAIXAs = false;
   IsAIX = false;
 

diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.h b/llvm/lib/Target/PowerPC/PPCSubtarget.h
index 3281816..6df9631 100644 (file)
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -168,6 +168,7 @@ protected:
   bool UsePPCPostRASchedStrategy;
   bool PairedVectorMemops;
   bool PredictableSelectIsExpensive;
+  bool HasFastMFLR;
   bool HasModernAIXAs;
   bool IsAIX;
 
@@ -316,6 +317,7 @@ public:
   bool hasPartwordAtomics() const { return HasPartwordAtomics; }
   bool hasQuadwordAtomics() const { return HasQuadwordAtomics; }
   bool hasDirectMove() const { return HasDirectMove; }
+  bool hasFastMFLR() const { return HasFastMFLR; }
 
   Align getPlatformStackAlignment() const {
     return Align(16);