[AArch64] Select saturating Neon instructions

This adds some extra patterns to select AArch64 Neon SQADD, UQADD, SQSUB
and UQSUB from the existing target independent sadd_sat, uadd_sat,
ssub_sat and usub_sat nodes.

It does not attempt to replace the existing int_aarch64_neon_uqadd
intrinsic nodes as they are apparently used for both scalar and vector,
and need to be legal on scalar types for some of the patterns to work.
The int_aarch64_neon_uqadd on scalar would move the two integers into
floating point registers, perform a Neon uqadd and move the value back.
I don't believe this is good idea for uadd_sat to do the same as the
scalar alternative is simpler (an adds with a csinv). For signed it may
be smaller, but I'm not sure about it being better.

So this just adds some extra patterns for the existing vector
instructions, matching on the _sat nodes.

Differential Revision: https://reviews.llvm.org/D69374

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -741,14 +741,20 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::MUL, MVT::v4i32, Custom);
     setOperationAction(ISD::MUL, MVT::v2i64, Custom);
 
-    // Vector reductions
     for (MVT VT : { MVT::v8i8, MVT::v4i16, MVT::v2i32,
                     MVT::v16i8, MVT::v8i16, MVT::v4i32, MVT::v2i64 }) {
+      // Vector reductions
       setOperationAction(ISD::VECREDUCE_ADD, VT, Custom);
       setOperationAction(ISD::VECREDUCE_SMAX, VT, Custom);
       setOperationAction(ISD::VECREDUCE_SMIN, VT, Custom);
       setOperationAction(ISD::VECREDUCE_UMAX, VT, Custom);
       setOperationAction(ISD::VECREDUCE_UMIN, VT, Custom);
+
+      // Saturates
+      setOperationAction(ISD::SADDSAT, VT, Legal);
+      setOperationAction(ISD::UADDSAT, VT, Legal);
+      setOperationAction(ISD::SSUBSAT, VT, Legal);
+      setOperationAction(ISD::USUBSAT, VT, Legal);
     }
     for (MVT VT : { MVT::v4f16, MVT::v2f32,
                     MVT::v8f16, MVT::v4f32, MVT::v2f64 }) {

llvm/lib/Target/AArch64/AArch64InstrFormats.td

@@ -5066,6 +5066,24 @@ multiclass SIMDThreeSameVector<bit U, bits<5> opc, string asm,
          [(set (v2i64 V128:$Rd), (OpNode (v2i64 V128:$Rn), (v2i64 V128:$Rm)))]>;
 }
 
+multiclass SIMDThreeSameVectorExtraPatterns<string inst, SDPatternOperator OpNode> {
+  def : Pat<(v8i8 (OpNode V64:$LHS, V64:$RHS)),
+          (!cast<Instruction>(inst#"v8i8") V64:$LHS, V64:$RHS)>;
+  def : Pat<(v4i16 (OpNode V64:$LHS, V64:$RHS)),
+          (!cast<Instruction>(inst#"v4i16") V64:$LHS, V64:$RHS)>;
+  def : Pat<(v2i32 (OpNode V64:$LHS, V64:$RHS)),
+          (!cast<Instruction>(inst#"v2i32") V64:$LHS, V64:$RHS)>;
+
+  def : Pat<(v16i8 (OpNode V128:$LHS, V128:$RHS)),
+          (!cast<Instruction>(inst#"v16i8") V128:$LHS, V128:$RHS)>;
+  def : Pat<(v8i16 (OpNode V128:$LHS, V128:$RHS)),
+          (!cast<Instruction>(inst#"v8i16") V128:$LHS, V128:$RHS)>;
+  def : Pat<(v4i32 (OpNode V128:$LHS, V128:$RHS)),
+          (!cast<Instruction>(inst#"v4i32") V128:$LHS, V128:$RHS)>;
+  def : Pat<(v2i64 (OpNode V128:$LHS, V128:$RHS)),
+          (!cast<Instruction>(inst#"v2i64") V128:$LHS, V128:$RHS)>;
+}
+
 // As above, but D sized elements unsupported.
 multiclass SIMDThreeSameVectorBHS<bit U, bits<5> opc, string asm,
                                   SDPatternOperator OpNode> {

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -3839,6 +3839,12 @@ defm SQRDMLAH : SIMDThreeSameVectorSQRDMLxHTiedHS<1,0b10000,"sqrdmlah",
 defm SQRDMLSH : SIMDThreeSameVectorSQRDMLxHTiedHS<1,0b10001,"sqrdmlsh",
                                                     int_aarch64_neon_sqsub>;
 
+// Extra saturate patterns, other than the intrinsics matches above
+defm : SIMDThreeSameVectorExtraPatterns<"SQADD", saddsat>;
+defm : SIMDThreeSameVectorExtraPatterns<"UQADD", uaddsat>;
+defm : SIMDThreeSameVectorExtraPatterns<"SQSUB", ssubsat>;
+defm : SIMDThreeSameVectorExtraPatterns<"UQSUB", usubsat>;
+
 defm AND : SIMDLogicalThreeVector<0, 0b00, "and", and>;
 defm BIC : SIMDLogicalThreeVector<0, 0b01, "bic",
                                   BinOpFrag<(and node:$LHS, (vnot node:$RHS))> >;

llvm/test/CodeGen/AArch64/sadd_sat.ll

@@ -88,15 +88,7 @@ define i4 @func3(i4 %x, i4 %y) nounwind {
 define <4 x i32> @vec(<4 x i32> %x, <4 x i32> %y) nounwind {
 ; CHECK-LABEL: vec:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    add v2.4s, v0.4s, v1.4s
-; CHECK-NEXT:    cmlt v4.4s, v2.4s, #0
-; CHECK-NEXT:    mvni v3.4s, #128, lsl #24
-; CHECK-NEXT:    cmlt v1.4s, v1.4s, #0
-; CHECK-NEXT:    cmgt v0.4s, v0.4s, v2.4s
-; CHECK-NEXT:    mvn v5.16b, v4.16b
-; CHECK-NEXT:    bsl v3.16b, v4.16b, v5.16b
-; CHECK-NEXT:    eor v0.16b, v1.16b, v0.16b
-; CHECK-NEXT:    bsl v0.16b, v3.16b, v2.16b
+; CHECK-NEXT:    sqadd v0.4s, v0.4s, v1.4s
 ; CHECK-NEXT:    ret
   %tmp = call <4 x i32> @llvm.sadd.sat.v4i32(<4 x i32> %x, <4 x i32> %y);
   ret <4 x i32> %tmp;