[RISCV] Accept [-128,255] instead of [0, 255] for pli.b (#153913)

pli.h and pli.w both accept signed immediates, so pli.b should too. But
unlike those instructions, pli.b doesn't do any extension so its ok to
accept an unsigned immediate as well.

Author: topperc

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -903,6 +903,7 @@ struct RISCVOperand final : public MCParsedAsmOperand {
            VK == RISCV::S_QC_ABS20;
   }
 
+  bool isSImm8Unsigned() const { return isSImm<8>() || isUImm<8>(); }
   bool isSImm10Unsigned() const { return isSImm<10>() || isUImm<10>(); }
 
   bool isUImm20LUI() const {
@@ -1199,6 +1200,14 @@ struct RISCVOperand final : public MCParsedAsmOperand {
     addExpr(Inst, getImm(), isRV64Imm());
   }
 
+  void addSImm8UnsignedOperands(MCInst &Inst, unsigned N) const {
+    assert(N == 1 && "Invalid number of operands!");
+    int64_t Imm;
+    [[maybe_unused]] bool IsConstant = evaluateConstantImm(getImm(), Imm);
+    assert(IsConstant);
+    Inst.addOperand(MCOperand::createImm(SignExtend64<8>(Imm)));
+  }
+
   void addSImm10UnsignedOperands(MCInst &Inst, unsigned N) const {
     assert(N == 1 && "Invalid number of operands!");
     int64_t Imm;
@@ -1547,6 +1556,9 @@ bool RISCVAsmParser::matchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
     return generateImmOutOfRangeError(
         Operands, ErrorInfo, 0, (1 << 9) - 8,
         "immediate must be a multiple of 8 bytes in the range");
+  case Match_InvalidSImm8Unsigned:
+    return generateImmOutOfRangeError(Operands, ErrorInfo, -(1 << 7),
+                                      (1 << 8) - 1);
   case Match_InvalidSImm10:
     return generateImmOutOfRangeError(Operands, ErrorInfo, -(1 << 9),
                                       (1 << 9) - 1);

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -346,6 +346,7 @@ enum OperandType : unsigned {
   OPERAND_SIMM5_PLUS1,
   OPERAND_SIMM6,
   OPERAND_SIMM6_NONZERO,
+  OPERAND_SIMM8,
   OPERAND_SIMM10,
   OPERAND_SIMM10_LSB0000_NONZERO,
   OPERAND_SIMM11,

llvm/lib/Target/RISCV/RISCVInstrInfoP.td

@@ -18,7 +18,26 @@
 // Operand and SDNode transformation definitions.
 //===----------------------------------------------------------------------===//
 
-def simm10 : RISCVSImmLeafOp<10>;
+def simm10 : RISCVSImmOp<10>;
+
+def SImm8UnsignedAsmOperand : SImmAsmOperand<8, "Unsigned"> {
+  let RenderMethod = "addSImm8UnsignedOperands";
+}
+
+// A 8-bit signed immediate allowing range [-128, 255]
+// but represented as [-128, 127].
+def simm8_unsigned : RISCVOp {
+  let ParserMatchClass = SImm8UnsignedAsmOperand;
+  let EncoderMethod = "getImmOpValue";
+  let DecoderMethod = "decodeSImmOperand<8>";
+  let OperandType = "OPERAND_SIMM10";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (!MCOp.evaluateAsConstantImm(Imm))
+      return false;
+    return isInt<8>(Imm);
+  }];
+}
 
 def SImm10UnsignedAsmOperand : SImmAsmOperand<10, "Unsigned"> {
   let RenderMethod = "addSImm10UnsignedOperands";
@@ -75,13 +94,13 @@ class PLUI_i<bits<7> funct7, string opcodestr>
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
 class PLI_B_i<bits<8> funct8, string opcodestr>
-    : RVInst<(outs GPR:$rd), (ins uimm8:$uimm8), opcodestr, "$rd, $uimm8", [],
-             InstFormatOther> {
-  bits<8> uimm8;
+    : RVInst<(outs GPR:$rd), (ins simm8_unsigned:$imm8), opcodestr,
+             "$rd, $imm8", [], InstFormatOther> {
+  bits<8> imm8;
   bits<5> rd;
 
   let Inst{31-24} = funct8;
-  let Inst{23-16} = uimm8;
+  let Inst{23-16} = imm8;
   let Inst{15}    = 0b0;
   let Inst{14-12} = 0b010;
   let Inst{11-7} = rd;

llvm/test/MC/RISCV/rv32p-invalid.s

@@ -4,7 +4,7 @@
 # Imm overflow
 pli.h a0, 0x400 # CHECK: :[[@LINE]]:11: error: immediate must be an integer in the range [-512, 511]
 plui.h a1, 0x400 # CHECK: :[[@LINE]]:12: error: immediate must be an integer in the range [-512, 1023]
-pli.b a0, 0x200 # CHECK: :[[@LINE]]:11: error: immediate must be an integer in the range [0, 255]
+pli.b a0, 0x200 # CHECK: :[[@LINE]]:11: error: immediate must be an integer in the range [-128, 255]
 
 pslli.b a6, a7, 100 # CHECK: :[[@LINE]]:17: error: immediate must be an integer in the range [0, 7]
 pslli.h ra, sp, 100 # CHECK: :[[@LINE]]:17: error: immediate must be an integer in the range [0, 15]

llvm/test/MC/RISCV/rv32p-valid.s

@@ -61,6 +61,9 @@ pli.h a5, 16
 # CHECK-ASM-AND-OBJ: pli.b a6, 16
 # CHECK-ASM: encoding: [0x1b,0x28,0x10,0xb4]
 pli.b a6, 16
+# CHECK-ASM-AND-OBJ: pli.b a6, -128
+# CHECK-ASM: encoding: [0x1b,0x28,0x80,0xb4]
+pli.b a6, -128
 # CHECK-ASM-AND-OBJ: psext.h.b a7, a0
 # CHECK-ASM: encoding: [0x9b,0x28,0x45,0xe0]
 psext.h.b a7, a0

llvm/test/MC/RISCV/rv64p-valid.s

@@ -79,6 +79,12 @@ pli.w a5, 5
 # CHECK-ASM-AND-OBJ: pli.b a6, 6
 # CHECK-ASM: encoding: [0x1b,0x28,0x06,0xb4]
 pli.b a6, 6
+# CHECK-ASM-AND-OBJ: pli.b a6, -1
+# CHECK-ASM: encoding: [0x1b,0x28,0xff,0xb4]
+pli.b a6, -1
+# CHECK-ASM-AND-OBJ: pli.b a6, -1
+# CHECK-ASM: encoding: [0x1b,0x28,0xff,0xb4]
+pli.b a6, 255
 # CHECK-ASM-AND-OBJ: psext.h.b t3, a2
 # CHECK-ASM: encoding: [0x1b,0x2e,0x46,0xe0]
 psext.h.b t3, a2