1 files changed, 45 insertions, 7 deletions
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 8f01210d666..5f08c9dd120 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -34109,6 +34109,41 @@ static SDValue detectUSatPattern(SDValue In, EVT VT) {
   return SDValue();
 }
 
+/// Detect patterns of truncation with signed saturation:
+/// (truncate (smin ((smax (x, signed_min_of_dest_type)),
+///                  signed_max_of_dest_type)) to dest_type)
+/// or:
+/// (truncate (smax ((smin (x, signed_max_of_dest_type)),
+///                  signed_min_of_dest_type)) to dest_type).
+/// Return the source value to be truncated or SDValue() if the pattern was not
+/// matched.
+static SDValue detectSSatPattern(SDValue In, EVT VT) {
+  unsigned NumDstBits = VT.getScalarSizeInBits();
+  unsigned NumSrcBits = In.getScalarValueSizeInBits();
+  assert(NumSrcBits > NumDstBits && "Unexpected types for truncate operation");
+
+  auto MatchMinMax = [](SDValue V, unsigned Opcode, const APInt &Limit) {
+    APInt C;
+    if (V.getOpcode() == Opcode &&
+        ISD::isConstantSplatVector(V.getOperand(1).getNode(), C) && C == Limit)
+      return V.getOperand(0);
+    return SDValue();
+  };
+
+  APInt SignedMax = APInt::getSignedMaxValue(NumDstBits).sext(NumSrcBits);
+  APInt SignedMin = APInt::getSignedMinValue(NumDstBits).sext(NumSrcBits);
+
+  if (SDValue SMin = MatchMinMax(In, ISD::SMIN, SignedMax))
+    if (SDValue SMax = MatchMinMax(SMin, ISD::SMAX, SignedMin))
+      return SMax;
+
+  if (SDValue SMax = MatchMinMax(In, ISD::SMAX, SignedMin))
+    if (SDValue SMin = MatchMinMax(SMax, ISD::SMIN, SignedMax))
+      return SMin;
+
+  return SDValue();
+}
+
 /// Detect a pattern of truncation with saturation:
 /// (truncate (umin (x, unsigned_max_of_dest_type)) to dest_type).
 /// The types should allow to use VPMOVUS* instruction on AVX512.
@@ -34121,15 +34156,18 @@ static SDValue detectAVX512USatPattern(SDValue In, EVT VT,
   return detectUSatPattern(In, VT);
 }
 
-static SDValue combineTruncateWithUSat(SDValue In, EVT VT, const SDLoc &DL,
-                                       SelectionDAG &DAG,
-                                       const X86Subtarget &Subtarget) {
+static SDValue combineTruncateWithSat(SDValue In, EVT VT, const SDLoc &DL,
+                                      SelectionDAG &DAG,
+                                      const X86Subtarget &Subtarget) {
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   if (!TLI.isTypeLegal(In.getValueType()) || !TLI.isTypeLegal(VT))
     return SDValue();
-  if (auto USatVal = detectUSatPattern(In, VT))
-    if (isSATValidOnAVX512Subtarget(In.getValueType(), VT, Subtarget))
+  if (isSATValidOnAVX512Subtarget(In.getValueType(), VT, Subtarget)) {
+    if (auto SSatVal = detectSSatPattern(In, VT))
+      return DAG.getNode(X86ISD::VTRUNCS, DL, VT, SSatVal);
+    if (auto USatVal = detectUSatPattern(In, VT))
       return DAG.getNode(X86ISD::VTRUNCUS, DL, VT, USatVal);
+  }
   return SDValue();
 }
 
@@ -35393,8 +35431,8 @@ static SDValue combineTruncate(SDNode *N, SelectionDAG &DAG,
   if (SDValue Avg = detectAVGPattern(Src, VT, DAG, Subtarget, DL))
     return Avg;
 
-  // Try to combine truncation with unsigned saturation.
-  if (SDValue Val = combineTruncateWithUSat(Src, VT, DL, DAG, Subtarget))
+  // Try to combine truncation with signed/unsigned saturation.
+  if (SDValue Val = combineTruncateWithSat(Src, VT, DL, DAG, Subtarget))
     return Val;
 
   // The bitcast source is a direct mmx result.