3 files changed, 22 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86.td b/llvm/lib/Target/X86/X86.td
index a799c1fda49..8f6d201bbb4 100644
--- a/llvm/lib/Target/X86/X86.td
+++ b/llvm/lib/Target/X86/X86.td
@@ -427,6 +427,11 @@ def FeatureFastHorizontalOps
         "Prefer horizontal vector math instructions (haddp, phsub, etc.) over "
         "normal vector instructions with shuffles", [FeatureSSE3]>;
 
+def FeatureFastScalarShiftMasks
+    : SubtargetFeature<
+        "fast-scalar-shift-masks", "HasFastScalarShiftMasks", "true",
+        "Prefer a left/right scalar logical shift pair over a shift+and pair">;
+
 def FeatureFastVectorShiftMasks
     : SubtargetFeature<
         "fast-vector-shift-masks", "HasFastVectorShiftMasks", "true",
@@ -784,6 +789,7 @@ def ProcessorFeatures {
                                                       FeatureSlowSHLD,
                                                       FeatureLAHFSAHF,
                                                       FeatureFast15ByteNOP,
+                                                      FeatureFastScalarShiftMasks,
                                                       FeatureFastVectorShiftMasks];
   list<SubtargetFeature> BtVer1Features = BtVer1InheritableFeatures;
 
@@ -825,6 +831,7 @@ def ProcessorFeatures {
                                                       FeatureSlowSHLD,
                                                       FeatureLAHFSAHF,
                                                       FeatureFast11ByteNOP,
+                                                      FeatureFastScalarShiftMasks,
                                                       FeatureBranchFusion];
   list<SubtargetFeature> BdVer1Features = BdVer1InheritableFeatures;
 
@@ -876,6 +883,7 @@ def ProcessorFeatures {
                                        FeatureFastBEXTR,
                                        FeatureFast15ByteNOP,
                                        FeatureBranchFusion,
+                                       FeatureFastScalarShiftMasks,
                                        FeatureMMX,
                                        FeatureMOVBE,
                                        FeatureMWAITX,
@@ -1092,20 +1100,22 @@ foreach P = ["athlon-4", "athlon-xp", "athlon-mp"] in {
 foreach P = ["k8", "opteron", "athlon64", "athlon-fx"] in {
   def : Proc<P, [FeatureX87, FeatureSlowUAMem16, FeatureCMPXCHG8B,
                  FeatureSSE2, Feature3DNowA, FeatureFXSR, FeatureNOPL,
-                 Feature64Bit, FeatureSlowSHLD, FeatureCMOV]>;
+                 Feature64Bit, FeatureSlowSHLD, FeatureCMOV,
+                 FeatureFastScalarShiftMasks]>;
 }
 
 foreach P = ["k8-sse3", "opteron-sse3", "athlon64-sse3"] in {
   def : Proc<P, [FeatureX87, FeatureSlowUAMem16, FeatureCMPXCHG8B, FeatureSSE3,
                  Feature3DNowA, FeatureFXSR, FeatureNOPL, FeatureCMPXCHG16B,
-                 FeatureSlowSHLD, FeatureCMOV, Feature64Bit]>;
+                 FeatureSlowSHLD, FeatureCMOV, Feature64Bit,
+                 FeatureFastScalarShiftMasks]>;
 }
 
 foreach P = ["amdfam10", "barcelona"] in {
   def : Proc<P, [FeatureX87, FeatureCMPXCHG8B, FeatureSSE4A, Feature3DNowA,
                  FeatureFXSR, FeatureNOPL, FeatureCMPXCHG16B, FeatureLZCNT,
                  FeaturePOPCNT, FeatureSlowSHLD, FeatureLAHFSAHF, FeatureCMOV,
-                 Feature64Bit]>;
+                 Feature64Bit, FeatureFastScalarShiftMasks]>;
 }
 
 // Bobcat
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 28bd08f57c1..43911a1b016 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5021,11 +5021,12 @@ bool X86TargetLowering::shouldFoldConstantShiftPairToMask(
           (N->getOpcode() == ISD::SRL &&
            N->getOperand(0).getOpcode() == ISD::SHL)) &&
          "Expected shift-shift mask");
-
-  if (Subtarget.hasFastVectorShiftMasks() && N->getValueType(0).isVector()) {
+  EVT VT = N->getValueType(0);
+  if ((Subtarget.hasFastVectorShiftMasks() && VT.isVector()) ||
+      (Subtarget.hasFastScalarShiftMasks() && !VT.isVector())) {
     // Only fold if the shift values are equal - so it folds to AND.
-    // TODO - we should fold if either is non-uniform but we don't do the
-    // fold for non-splats yet.
+    // TODO - we should fold if either is a non-uniform vector but we don't do
+    // the fold for non-splats yet.
     return N->getOperand(1) == N->getOperand(0).getOperand(1);
   }
   return TargetLoweringBase::shouldFoldConstantShiftPairToMask(N, Level);
diff --git a/llvm/lib/Target/X86/X86Subtarget.h b/llvm/lib/Target/X86/X86Subtarget.h
index 3b11bb12f62..43d4ab71318 100644
--- a/llvm/lib/Target/X86/X86Subtarget.h
+++ b/llvm/lib/Target/X86/X86Subtarget.h
@@ -396,6 +396,9 @@ protected:
   /// Try harder to combine to horizontal vector ops if they are fast.
   bool HasFastHorizontalOps = false;
 
+  /// Prefer a left/right scalar logical shifts pair over a shift+and pair.
+  bool HasFastScalarShiftMasks = false;
+
   /// Prefer a left/right vector logical shifts pair over a shift+and pair.
   bool HasFastVectorShiftMasks = false;
 
@@ -650,6 +653,7 @@ public:
   bool hasFastSHLDRotate() const { return HasFastSHLDRotate; }
   bool hasFastBEXTR() const { return HasFastBEXTR; }
   bool hasFastHorizontalOps() const { return HasFastHorizontalOps; }
+  bool hasFastScalarShiftMasks() const { return HasFastScalarShiftMasks; }
   bool hasFastVectorShiftMasks() const { return HasFastVectorShiftMasks; }
   bool hasMacroFusion() const { return HasMacroFusion; }
   bool hasBranchFusion() const { return HasBranchFusion; }