[mips][ias] Range check uimm5 operands and fix several bugs this reve…

…aled. Summary: The bugs were: * append, prepend, and balign were not tested * balign takes a uimm2 not a uimm5. * drotr32 was correctly implemented with a uimm5 but the tests expected '52' to be valid. * li/la were implemented with a uimm5 instead of simm32. simm32 isn't completely correct either but I'll fix that when I get to simm32. A notable omission are some of the shift instructions. Several of these have been implemented using a single uimm6 instruction (rather than two uimm5 instructions and a CodeGen-only uimm6 pseudo). These will be updated in the uimm6 patch. Reviewers: vkalintiris Subscribers: llvm-commits, dsanders Differential Revision: http://reviews.llvm.org/D14712 llvm-svn: 254164
llvm · Nov 26, 2015 · daa4b6f · daa4b6f
1 parent e4fbec4
commit daa4b6f
Showing 23 changed files with 312 additions and 135 deletions.
diff --git a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -928,12 +928,13 @@ class MipsOperand : public MCParsedAsmOperand {
     Inst.addOperand(MCOperand::createReg(getHWRegsReg()));
   }
 
-  template <unsigned Bits, int Offset = 0>
+  template <unsigned Bits, int Offset = 0, int AdjustOffset = 0>
   void addConstantUImmOperands(MCInst &Inst, unsigned N) const {
     assert(N == 1 && "Invalid number of operands!");
     uint64_t Imm = getConstantImm() - Offset;
     Imm &= (1 << Bits) - 1;
     Imm += Offset;
+    Imm += AdjustOffset;
     Inst.addOperand(MCOperand::createImm(Imm));
   }
 
@@ -1034,8 +1035,10 @@ class MipsOperand : public MCParsedAsmOperand {
       && (getConstantMemOff() % 4 == 0) && getMemBase()->isRegIdx()
       && (getMemBase()->getGPR32Reg() == Mips::SP);
   }
-  bool isUImm5Lsl2() const {
-    return (isImm() && isConstantImm() && isShiftedUInt<5, 2>(getConstantImm()));
+  template <unsigned Bits, unsigned ShiftLeftAmount>
+  bool isScaledUImm() const {
+    return isConstantImm() &&
+           isShiftedUInt<Bits, ShiftLeftAmount>(getConstantImm());
   }
   bool isRegList16() const {
     if (!isRegList())
@@ -1620,32 +1623,6 @@ bool MipsAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
         }
         break;
 
-      case Mips::CINS:
-      case Mips::CINS32:
-      case Mips::EXTS:
-      case Mips::EXTS32:
-        assert(MCID.getNumOperands() == 4 && "unexpected number of operands");
-        // Check length
-        Opnd = Inst.getOperand(3);
-        if (!Opnd.isImm())
-          return Error(IDLoc, "expected immediate operand kind");
-        Imm = Opnd.getImm();
-        if (Imm < 0 || Imm > 31)
-          return Error(IDLoc, "immediate operand value out of range");
-        // Check position
-        Opnd = Inst.getOperand(2);
-        if (!Opnd.isImm())
-          return Error(IDLoc, "expected immediate operand kind");
-        Imm = Opnd.getImm();
-        if (Imm < 0 || Imm > (Opcode == Mips::CINS ||
-                              Opcode == Mips::EXTS ? 63 : 31))
-          return Error(IDLoc, "immediate operand value out of range");
-        if (Imm > 31) {
-          Inst.setOpcode(Opcode == Mips::CINS ? Mips::CINS32 : Mips::EXTS32);
-          Inst.getOperand(2).setImm(Imm - 32);
-        }
-        break;
-
       case Mips::SEQi:
       case Mips::SNEi:
         assert(MCID.getNumOperands() == 3 && "unexpected number of operands");
@@ -1909,16 +1886,6 @@ bool MipsAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
         if (Imm < 0 || Imm > 60 || (Imm % 4 != 0))
           return Error(IDLoc, "immediate operand value out of range");
         break;
-      case Mips::PREFX_MM:
-      case Mips::CACHE:
-      case Mips::PREF:
-        Opnd = Inst.getOperand(2);
-        if (!Opnd.isImm())
-          return Error(IDLoc, "expected immediate operand kind");
-        Imm = Opnd.getImm();
-        if (!isUInt<5>(Imm))
-          return Error(IDLoc, "immediate operand value out of range");
-        break;
       case Mips::ADDIUPC_MM:
         MCOperand Opnd = Inst.getOperand(1);
         if (!Opnd.isImm())
@@ -3666,6 +3633,20 @@ bool MipsAsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
   case Match_UImm4_0:
     return Error(RefineErrorLoc(IDLoc, Operands, ErrorInfo),
                  "expected 4-bit unsigned immediate");
+  case Match_UImm5_0:
+    return Error(RefineErrorLoc(IDLoc, Operands, ErrorInfo),
+                 "expected 5-bit unsigned immediate");
+  case Match_UImm5_32:
+    return Error(RefineErrorLoc(IDLoc, Operands, ErrorInfo),
+                 "expected immediate in range 32 .. 63");
+  case Match_UImm5_0_Report_UImm6:
+    // This is used on UImm5 operands that have a corresponding UImm5_32
+    // operand to avoid confusing the user.
+    return Error(RefineErrorLoc(IDLoc, Operands, ErrorInfo),
+                 "expected 6-bit unsigned immediate");
+  case Match_UImm5_Lsl2:
+    return Error(RefineErrorLoc(IDLoc, Operands, ErrorInfo),
+                 "expected both 7-bit unsigned immediate and multiple of 4");
   }
 
   llvm_unreachable("Implement any new match types added!");

diff --git a/llvm/lib/Target/Mips/MicroMipsInstrInfo.td b/llvm/lib/Target/Mips/MicroMipsInstrInfo.td
@@ -13,19 +13,6 @@ def simm12 : Operand<i32> {
   let DecoderMethod = "DecodeSimm12";
 }
 
-def MipsUimm5Lsl2AsmOperand : AsmOperandClass {
-  let Name = "Uimm5Lsl2";
-  let RenderMethod = "addImmOperands";
-  let ParserMethod = "parseImm";
-  let PredicateMethod = "isUImm5Lsl2";
-}
-
-def uimm5_lsl2 : Operand<OtherVT> {
-  let EncoderMethod = "getUImm5Lsl2Encoding";
-  let DecoderMethod = "DecodeUImm5lsl2";
-  let ParserMatchClass = MipsUimm5Lsl2AsmOperand;
-}
-
 def uimm6_lsl2 : Operand<i32> {
   let EncoderMethod = "getUImm6Lsl2Encoding";
   let DecoderMethod = "DecodeUImm6Lsl2";

diff --git a/llvm/lib/Target/Mips/Mips64InstrInfo.td b/llvm/lib/Target/Mips/Mips64InstrInfo.td
@@ -16,10 +16,6 @@
 //===----------------------------------------------------------------------===//
 
 // Unsigned Operand
-def uimm5_64      : Operand<i64> {
-  let PrintMethod = "printUnsignedImm";
-}
-
 def uimm16_64      : Operand<i64> {
   let PrintMethod = "printUnsignedImm";
 }
@@ -343,8 +339,8 @@ class SetCC64_I<string opstr, PatFrag cond_op>:
 }
 
 class CBranchBitNum<string opstr, DAGOperand opnd, PatFrag cond_op,
-                    RegisterOperand RO, bits<64> shift = 1> :
-  InstSE<(outs), (ins RO:$rs, uimm5_64:$p, opnd:$offset),
+                    RegisterOperand RO, Operand ImmOp, bits<64> shift = 1> :
+  InstSE<(outs), (ins RO:$rs, ImmOp:$p, opnd:$offset),
          !strconcat(opstr, "\t$rs, $p, $offset"),
          [(brcond (i32 (cond_op (and RO:$rs, (shl shift, immZExt5_64:$p)), 0)),
                   bb:$offset)], II_BBIT, FrmI, opstr> {
@@ -365,14 +361,17 @@ def BADDu  : ArithLogicR<"baddu", GPR64Opnd, 1, II_BADDU>,
                               ADD_FM<0x1c, 0x28>;
 
 // Branch on Bit Clear /+32
-def BBIT0  : CBranchBitNum<"bbit0", brtarget, seteq, GPR64Opnd>, BBIT_FM<0x32>;
-def BBIT032: CBranchBitNum<"bbit032", brtarget, seteq, GPR64Opnd, 0x100000000>,
+def BBIT0  : CBranchBitNum<"bbit0", brtarget, seteq, GPR64Opnd,
+                           uimm5_64_report_uimm6>, BBIT_FM<0x32>;
+def BBIT032: CBranchBitNum<"bbit032", brtarget, seteq, GPR64Opnd, uimm5_64,
+                           0x100000000>,
                            BBIT_FM<0x36>;
 
 // Branch on Bit Set /+32
-def BBIT1  : CBranchBitNum<"bbit1", brtarget, setne, GPR64Opnd>, BBIT_FM<0x3a>;
-def BBIT132: CBranchBitNum<"bbit132", brtarget, setne, GPR64Opnd, 0x100000000>,
-                           BBIT_FM<0x3e>;
+def BBIT1  : CBranchBitNum<"bbit1", brtarget, setne, GPR64Opnd,
+                           uimm5_64_report_uimm6>, BBIT_FM<0x3a>;
+def BBIT132: CBranchBitNum<"bbit132", brtarget, setne, GPR64Opnd, uimm5_64,
+                           0x100000000>, BBIT_FM<0x3e>;
 
 // Multiply Doubleword to GPR
 let Defs = [HI0, LO0, P0, P1, P2] in
@@ -634,6 +633,38 @@ def : MipsInstAlias<"syncw",      (SYNC 0x4), 0>;
 def : MipsInstAlias<"syncws",     (SYNC 0x5), 0>;
 }
 
+// cnMIPS Aliases.
+
+// bbit* with $p 32-63 converted to bbit*32 with $p 0-31
+def : MipsInstAlias<"bbit0 $rs, $p, $offset",
+                    (BBIT032 GPR64Opnd:$rs, uimm5_plus32_normalize_64:$p,
+                             brtarget:$offset), 0>,
+      ASE_CNMIPS;
+def : MipsInstAlias<"bbit1 $rs, $p, $offset",
+                    (BBIT132 GPR64Opnd:$rs, uimm5_plus32_normalize_64:$p,
+                             brtarget:$offset), 0>,
+      ASE_CNMIPS;
+
+// exts with $pos 32-63 in converted to exts32 with $pos 0-31
+def : MipsInstAlias<"exts $rt, $rs, $pos, $lenm1",
+                    (EXTS32 GPR64Opnd:$rt, GPR64Opnd:$rs,
+                            uimm5_plus32_normalize:$pos, uimm5:$lenm1), 0>,
+      ASE_CNMIPS;
+def : MipsInstAlias<"exts $rt, $pos, $lenm1",
+                    (EXTS32 GPR64Opnd:$rt, GPR64Opnd:$rt,
+                            uimm5_plus32_normalize:$pos, uimm5:$lenm1), 0>,
+      ASE_CNMIPS;
+
+// cins with $pos 32-63 in converted to cins32 with $pos 0-31
+def : MipsInstAlias<"cins $rt, $rs, $pos, $lenm1",
+                    (CINS32 GPR64Opnd:$rt, GPR64Opnd:$rs,
+                            uimm5_plus32_normalize:$pos, uimm5:$lenm1), 0>,
+      ASE_CNMIPS;
+def : MipsInstAlias<"cins $rt, $pos, $lenm1",
+                    (CINS32 GPR64Opnd:$rt, GPR64Opnd:$rt,
+                            uimm5_plus32_normalize:$pos, uimm5:$lenm1), 0>,
+      ASE_CNMIPS;
+
 //===----------------------------------------------------------------------===//
 // Assembler Pseudo Instructions
 //===----------------------------------------------------------------------===//

diff --git a/llvm/lib/Target/Mips/MipsDSPInstrInfo.td b/llvm/lib/Target/Mips/MipsDSPInstrInfo.td
@@ -372,12 +372,12 @@ class ADDUH_QB_DESC_BASE<string instr_asm, SDPatternOperator OpNode,
 }
 
 class APPEND_DESC_BASE<string instr_asm, SDPatternOperator OpNode,
-                       SDPatternOperator ImmOp, InstrItinClass itin> {
+                       Operand ImmOp, SDPatternOperator Imm, InstrItinClass itin> {
   dag OutOperandList = (outs GPR32Opnd:$rt);
-  dag InOperandList = (ins GPR32Opnd:$rs, uimm5:$sa, GPR32Opnd:$src);
+  dag InOperandList = (ins GPR32Opnd:$rs, ImmOp:$sa, GPR32Opnd:$src);
   string AsmString = !strconcat(instr_asm, "\t$rt, $rs, $sa");
   list<dag> Pattern =  [(set GPR32Opnd:$rt,
-                        (OpNode GPR32Opnd:$src, GPR32Opnd:$rs, ImmOp:$sa))];
+                        (OpNode GPR32Opnd:$src, GPR32Opnd:$rs, Imm:$sa))];
   InstrItinClass Itinerary = itin;
   string Constraints = "$src = $rt";
 }
@@ -1074,14 +1074,14 @@ class SHRLV_PH_DESC : SHLL_QB_R3_DESC_BASE<"shrlv.ph", int_mips_shrl_ph,
                                            NoItinerary, DSPROpnd>;
 
 // Misc
-class APPEND_DESC : APPEND_DESC_BASE<"append", int_mips_append, immZExt5,
+class APPEND_DESC : APPEND_DESC_BASE<"append", int_mips_append, uimm5, immZExt5,
                                      NoItinerary>;
 
-class BALIGN_DESC : APPEND_DESC_BASE<"balign", int_mips_balign, immZExt2,
+class BALIGN_DESC : APPEND_DESC_BASE<"balign", int_mips_balign, uimm2, immZExt2,
                                      NoItinerary>;
 
-class PREPEND_DESC : APPEND_DESC_BASE<"prepend", int_mips_prepend, immZExt5,
-                                      NoItinerary>;
+class PREPEND_DESC : APPEND_DESC_BASE<"prepend", int_mips_prepend, uimm5,
+                                      immZExt5, NoItinerary>;
 
 // Pseudos.
 def BPOSGE32_PSEUDO : BPOSGE32_PSEUDO_DESC_BASE<int_mips_bposge32,

diff --git a/llvm/lib/Target/Mips/MipsInstrInfo.td b/llvm/lib/Target/Mips/MipsInstrInfo.td
@@ -311,6 +311,10 @@ class INSN_MIPS5_32R2_NOT_32R6_64R6 {
   list<Predicate> InsnPredicates = [HasMips5_32r2, NotMips32r6, NotMips64r6];
 }
 
+class ASE_CNMIPS {
+  list<Predicate> InsnPredicates = [HasCnMips];
+}
+
 class ASE_MSA {
   list<Predicate> InsnPredicates = [HasMSA];
 }
@@ -390,8 +394,29 @@ class ConstantUImmAsmOperandClass<int Bits, list<AsmOperandClass> Supers = [],
   let DiagnosticType = "UImm" # Bits # "_" # Offset;
 }
 
+def ConstantUImm5Plus32NormalizeAsmOperandClass
+    : ConstantUImmAsmOperandClass<5, [], 32> {
+  // We must also subtract 32 when we render the operand.
+  let RenderMethod = "addConstantUImmOperands<5, 32, -32>";
+}
+def ConstantUImm5Lsl2AsmOperandClass : AsmOperandClass {
+  let Name = "UImm5Lsl2";
+  let RenderMethod = "addImmOperands";
+  let PredicateMethod = "isScaledUImm<5, 2>";
+  let SuperClasses = [];
+  let DiagnosticType = "UImm5_Lsl2";
+}
+def ConstantUImm5ReportUImm6AsmOperandClass
+    : ConstantUImmAsmOperandClass<5, []> {
+  let Name = "ConstantUImm5_0_Report_UImm6";
+  let DiagnosticType = "UImm5_0_Report_UImm6";
+}
+def ConstantUImm5AsmOperandClass
+    : ConstantUImmAsmOperandClass<5, []>;
 def ConstantUImm4AsmOperandClass
-    : ConstantUImmAsmOperandClass<4, []>;
+    : ConstantUImmAsmOperandClass<
+          4, [ConstantUImm5AsmOperandClass,
+              ConstantUImm5Plus32NormalizeAsmOperandClass]>;
 def ConstantUImm3AsmOperandClass
     : ConstantUImmAsmOperandClass<3, [ConstantUImm4AsmOperandClass]>;
 def ConstantUImm2Plus1AsmOperandClass
@@ -453,8 +478,8 @@ def simm18_lsl3 : Operand<i32> {
   let ParserMatchClass = MipsJumpTargetAsmOperand;
 }
 
-def simm20      : Operand<i32> {
-}
+def simm20      : Operand<i32>;
+def simm32      : Operand<i32>;
 
 def uimm20      : Operand<i32> {
 }
@@ -481,7 +506,7 @@ def uimmz       : Operand<i32> {
 }
 
 // Unsigned Operands
-foreach I = {1, 2, 3, 4} in
+foreach I = {1, 2, 3, 4, 5} in
   def uimm # I : Operand<i32> {
     let PrintMethod = "printUnsignedImm";
     let ParserMatchClass =
@@ -495,8 +520,34 @@ def uimm2_plus1 : Operand<i32> {
   let ParserMatchClass = ConstantUImm2Plus1AsmOperandClass;
 }
 
-def uimm5       : Operand<i32> {
+def uimm5_plus32_normalize : Operand<i32> {
+  let PrintMethod = "printUnsignedImm";
+  let ParserMatchClass = ConstantUImm5Plus32NormalizeAsmOperandClass;
+}
+
+def uimm5_lsl2 : Operand<OtherVT> {
+  let EncoderMethod = "getUImm5Lsl2Encoding";
+  let DecoderMethod = "DecodeUImm5lsl2";
+  let ParserMatchClass = ConstantUImm5Lsl2AsmOperandClass;
+}
+
+def uimm5_plus32_normalize_64 : Operand<i64> {
+  let PrintMethod = "printUnsignedImm";
+  let ParserMatchClass = ConstantUImm5Plus32NormalizeAsmOperandClass;
+}
+
+foreach I = {5} in
+  def uimm # I # _64 : Operand<i64> {
+    let PrintMethod = "printUnsignedImm";
+    let ParserMatchClass =
+        !cast<AsmOperandClass>("ConstantUImm" # I # "AsmOperandClass");
+  }
+
+// Like uimm5_64 but reports a less confusing error for 32-63 when
+// an instruction alias permits that.
+def uimm5_64_report_uimm6 : Operand<i64> {
   let PrintMethod = "printUnsignedImm";
+  let ParserMatchClass = ConstantUImm5ReportUImm6AsmOperandClass;
 }
 
 def uimm6 : Operand<i32> {
@@ -1847,7 +1898,7 @@ def : MipsInstAlias<"sync",
 class LoadImmediate32<string instr_asm, Operand Od, RegisterOperand RO> :
   MipsAsmPseudoInst<(outs RO:$rt), (ins Od:$imm32),
                      !strconcat(instr_asm, "\t$rt, $imm32")> ;
-def LoadImm32 : LoadImmediate32<"li", uimm5, GPR32Opnd>;
+def LoadImm32 : LoadImmediate32<"li", simm32, GPR32Opnd>;
 
 class LoadAddressFromReg32<string instr_asm, Operand MemOpnd,
                            RegisterOperand RO> :
@@ -1858,7 +1909,7 @@ def LoadAddrReg32 : LoadAddressFromReg32<"la", mem, GPR32Opnd>;
 class LoadAddressFromImm32<string instr_asm, Operand Od, RegisterOperand RO> :
   MipsAsmPseudoInst<(outs RO:$rt), (ins Od:$imm32),
                      !strconcat(instr_asm, "\t$rt, $imm32")> ;
-def LoadAddrImm32 : LoadAddressFromImm32<"la", uimm5, GPR32Opnd>;
+def LoadAddrImm32 : LoadAddressFromImm32<"la", simm32, GPR32Opnd>;
 
 def JalTwoReg : MipsAsmPseudoInst<(outs GPR32Opnd:$rd), (ins GPR32Opnd:$rs),
                       "jal\t$rd, $rs"> ;

diff --git a/llvm/test/MC/Mips/cnmips/invalid.s b/llvm/test/MC/Mips/cnmips/invalid.s
@@ -0,0 +1,15 @@
+# Instructions that are invalid
+#
+# RUN: not llvm-mc %s -triple=mips64-unknown-linux -show-encoding -mcpu=octeon 2>%t1
+# RUN: FileCheck %s < %t1
+
+    .set noat
+foo:
+    bbit0 $19, -1, foo   # CHECK: :[[@LINE]]:16: error: expected 6-bit unsigned immediate
+    bbit0 $19, 64, foo   # CHECK: :[[@LINE]]:16: error: expected 6-bit unsigned immediate
+    bbit032 $19, -1, foo # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
+    bbit032 $19, 32, foo # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
+    bbit1 $19, -1, foo   # CHECK: :[[@LINE]]:16: error: expected 6-bit unsigned immediate
+    bbit1 $19, 64, foo   # CHECK: :[[@LINE]]:16: error: expected 6-bit unsigned immediate
+    bbit132 $19, -1, foo # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
+    bbit132 $19, 32, foo # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
diff --git a/llvm/test/MC/Mips/dspr2/invalid.s b/llvm/test/MC/Mips/dspr2/invalid.s
@@ -1,6 +1,17 @@
-# RUN: not llvm-mc %s -triple=mips-unknown-unknown -show-encoding -mattr=dspr2 2>%t1
+# Instructions that are invalid
+#
+# RUN: not llvm-mc %s -triple=mips-unknown-linux -mattr=+dspr2 -show-encoding 2>%t1
 # RUN: FileCheck %s < %t1
-
+  append $2, $3, -1             # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
+  append $2, $3, 32             # CHECK: :[[@LINE]]:18: error: expected 5-bit unsigned immediate
+  balign $2, $3, -1             # CHECK: :[[@LINE]]:18: error: expected 2-bit unsigned immediate
+  balign $2, $3, 4              # CHECK: :[[@LINE]]:18: error: expected 2-bit unsigned immediate
+  precr_sra.ph.w $24, $25, -1   # CHECK: :[[@LINE]]:28: error: expected 5-bit unsigned immediate
+  precr_sra.ph.w $24, $25, 32   # CHECK: :[[@LINE]]:28: error: expected 5-bit unsigned immediate
+  precr_sra_r.ph.w $25 ,$26, -1 # CHECK: :[[@LINE]]:30: error: expected 5-bit unsigned immediate
+  precr_sra_r.ph.w $25 ,$26, 32 # CHECK: :[[@LINE]]:30: error: expected 5-bit unsigned immediate
+  prepend $2, $3, -1            # CHECK: :[[@LINE]]:19: error: expected 5-bit unsigned immediate
+  prepend $2, $3, 32            # CHECK: :[[@LINE]]:19: error: expected 5-bit unsigned immediate
   shra.qb $3, $4, 8        # CHECK: :[[@LINE]]:19: error: expected 3-bit unsigned immediate
   shra.qb $3, $4, -1       # CHECK: :[[@LINE]]:19: error: expected 3-bit unsigned immediate
   shra_r.qb $3, $4, 8      # CHECK: :[[@LINE]]:21: error: expected 3-bit unsigned immediate

diff --git a/llvm/test/MC/Mips/dspr2/valid.s b/llvm/test/MC/Mips/dspr2/valid.s
@@ -43,3 +43,6 @@
   mflo $15                     # CHECK: mflo $15                       # encoding: [0x00,0x00,0x78,0x12]
   mthi $16                     # CHECK: mthi $16                       # encoding: [0x02,0x00,0x00,0x11]
   mtlo $17                     # CHECK: mtlo $17                       # encoding: [0x02,0x20,0x00,0x13]
+  append $2, $3, 3             # CHECK: append $2, $3, 3               # encoding: [0x7c,0x62,0x18,0x31]
+  balign $4, $5, 1             # CHECK: balign $4, $5, 1               # encoding: [0x7c,0xa4,0x0c,0x31]
+  prepend $6, $7, 4            # CHECK: prepend $6, $7, 4              # encoding: [0x7c,0xe6,0x20,0x71]