5 files changed, 15 insertions, 12 deletions

diff --git a/llvm/lib/Target/X86/X86.td b/llvm/lib/Target/X86/X86.td
index 99d6c6932ae..c6ded683ebc 100644
--- a/llvm/lib/Target/X86/X86.td
+++ b/llvm/lib/Target/X86/X86.td
@@ -273,11 +273,14 @@ def FeatureFastSHLDRotate
           "fast-shld-rotate", "HasFastSHLDRotate", "true",
           "SHLD can be used as a faster rotate">;
 
-// String operations (e.g. REP MOVS) are fast. See "REP String Enhancement" in
-// the Intel Software Development Manual.
-def FeatureFastString
+// Ivy Bridge and newer processors have enhanced REP MOVSB and STOSB (aka
+// "string operations"). See "REP String Enhancement" in the Intel Software
+// Development Manual. This feature essentially meanis that REP MOVSB will copy
+// using the largest available size instead of copying bytes one by one, making
+// it at least as fast as REPMOVS{W,D,Q}.
+def FeatureERMSB
     : SubtargetFeature<
-          "fast-string", "HasFastString", "true",
+          "ermsb", "HasERMSB", "true",
           "REP MOVS/STOS are fast">;
 
 //===----------------------------------------------------------------------===//
@@ -505,7 +508,7 @@ def HSWFeatures : ProcessorFeatures<IVBFeatures.Value, [
   FeatureAVX2,
   FeatureBMI,
   FeatureBMI2,
-  FeatureFastString,
+  FeatureERMSB,
   FeatureFMA,
   FeatureLZCNT,
   FeatureMOVBE,
diff --git a/llvm/lib/Target/X86/X86InstrInfo.td b/llvm/lib/Target/X86/X86InstrInfo.td
index 456a204bafa..c3def461afd 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.td
+++ b/llvm/lib/Target/X86/X86InstrInfo.td
@@ -897,7 +897,7 @@ def NotSlowIncDec : Predicate<"!Subtarget->slowIncDec()">;
 def HasFastMem32 : Predicate<"!Subtarget->isUnalignedMem32Slow()">;
 def HasFastLZCNT : Predicate<"Subtarget->hasFastLZCNT()">;
 def HasFastSHLDRotate : Predicate<"Subtarget->hasFastSHLDRotate()">;
-def HasFastString : Predicate<"Subtarget->hasFastString()">;
+def HasERMSB : Predicate<"Subtarget->hasERMSB()">;
 def HasMFence    : Predicate<"Subtarget->hasMFence()">;
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
index d893738d068..f09040bfe88 100644
--- a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
+++ b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
@@ -215,8 +215,8 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemcpy(
     return SDValue();
 
   MVT AVT;
-  if (Subtarget.hasFastString())
-    // If the target has fast strings, then it's at least as fast to use
+  if (Subtarget.hasERMSB())
+    // If the target has enhanced REPMOVSB, then it's at least as fast to use
     // REP MOVSB instead of REP MOVS{W,D,Q}, and it avoids having to handle
     // BytesLeft.
     AVT = MVT::i8;
diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 0bd29a5a27d..4154530d04e 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -303,7 +303,7 @@ void X86Subtarget::initializeEnvironment() {
   HasFastVectorFSQRT = false;
   HasFastLZCNT = false;
   HasFastSHLDRotate = false;
-  HasFastString = false;
+  HasERMSB = false;
   HasSlowDivide32 = false;
   HasSlowDivide64 = false;
   PadShortFunctions = false;
diff --git a/llvm/lib/Target/X86/X86Subtarget.h b/llvm/lib/Target/X86/X86Subtarget.h
index 2b858c28e04..fd057f36c89 100644
--- a/llvm/lib/Target/X86/X86Subtarget.h
+++ b/llvm/lib/Target/X86/X86Subtarget.h
@@ -232,8 +232,8 @@ protected:
   /// True if SHLD based rotate is fast.
   bool HasFastSHLDRotate;
 
-  /// True if the processor has fast REP MOVS.
-  bool HasFastString;
+  /// True if the processor has enhanced REP MOVSB/STOSB.
+  bool HasERMSB;
 
   /// True if the short functions should be padded to prevent
   /// a stall when returning too early.
@@ -475,7 +475,7 @@ public:
   bool hasFastVectorFSQRT() const { return HasFastVectorFSQRT; }
   bool hasFastLZCNT() const { return HasFastLZCNT; }
   bool hasFastSHLDRotate() const { return HasFastSHLDRotate; }
-  bool hasFastString() const { return HasFastString; }
+  bool hasERMSB() const { return HasERMSB; }
   bool hasSlowDivide32() const { return HasSlowDivide32; }
   bool hasSlowDivide64() const { return HasSlowDivide64; }
   bool padShortFunctions() const { return PadShortFunctions; }