[RISCV][MC] Add support for evaluating constant symbols as immediates

[asb]

Summary

This further improves compatibility with GNU as, allowing input such as the following to be assembled:

.equ CONST, 0x123456
li a0, CONST
addi a0, a0, %lo(CONST)

.equ CONST, 1
slli a0, a0, CONST

Note that we don't have perfect compatibility with gas, as it will avoid emitting a relocation in this case:

addi a0, a0, %lo(CONST2)
.equ CONST2, 0x123456

[shiva0217]

Hi Alex, another solution could be calling parseExpression for AsmToken::Identifier in RISCVAsmParser::parseImmediate instead of calling parseIdentifier.

case AsmToken::String:
case AsmToken::Identifier: {
  if (getParser().parseExpression(Res))
    return MatchOperand_ParseFail;
  break;
}

parseExpression will call parsePrimaryExpr which contain the logical to call parseIdentifier and also try to get the symbol value when the symbol is variable.
What do you think?

[asb]

Thanks Shiva, that seems like a better approach. It also allows for parsing CONST+1 etc. This needs more test coverage though. From an initial look, it seems lui a0, CONST+1 has a problem when using parsePrimaryExpr that needs investigating further.

[asb]

As suggested my Shiva, this patch has been updated to allow AsmParser::parseExpression to do the work when parsing an identifier.

I mentioned previously that I encountered an issue when trying to switch to this approach, but I'm not longer able to reproduce (so it was probably a mistake on my part).

Note that constant symbols can't be used with CSR operations. That would require changes toparseCSRSystemRegister. Same for parseBareSymbol (used in e.g. the call pseudoinstruction). Given that this patch is an incremental improvement that makes sense on its own, I'd prefer to follow up with separate patches for the other cases.

Does this look good to you?

[shiva0217]

Hi Alex,
Thanks for the updates, looks good to me.

lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

static bool evaluateConstantImm(const MCExpr *Expr, int64_t &Imm,
     }
 
     if (auto CE = dyn_cast<MCConstantExpr>(Expr)) {
       VK = RISCVMCExpr::VK_RISCV_None;
       Imm = CE->getValue();
       return true;
     }
 
+    if (auto SRE = dyn_cast<MCSymbolRefExpr>(Expr)) {
+      if (SRE->getKind() != MCSymbolRefExpr::VK_None)
+        return false;
+      VK = RISCVMCExpr::VK_RISCV_None;
+      const MCSymbol &Sym = SRE->getSymbol();
+      if (!Sym.isVariable())
+        return false;
+      if (auto CE = dyn_cast<MCConstantExpr>(
+              Sym.getVariableValue(/*SetUsed*/ false))) {
+        Imm = CE->getValue();
+        return true;
+      }
+    }
+
     return false;
   }
 
   // True if operand is a symbol with no modifiers, or a constant with no
   // modifiers and isShiftedInt<N-1, 1>(Op).
   template <int N> bool isBareSimmNLsb0() const {
     int64_t Imm;
     RISCVMCExpr::VariantKind VK;

test/MC/RISCV/rv32i-aliases-valid.s

 # CHECK-EXPAND: lui a2, 524288
 li x12, -0x80000000
 
 # CHECK-EXPAND: lui a2, 524288
 li x12, 0x80000000
 # CHECK-EXPAND: addi a2, zero, -1
 li x12, 0xFFFFFFFF
 
+.equ CONST, 0x123456
+# CHECK-EXPAND: lui a0, 291
+# CHECK-EXPAND: addi a0, a0, 1110
+li a0, CONST
+
+.equ CONST, 0x654321
+# CHECK-EXPAND: lui a0, 1620
+# CHECK-EXPAND: addi a0, a0, 801
+li a0, CONST
+
 # CHECK-INST: csrrs t4, 3202, zero
 # CHECK-ALIAS: rdinstreth t4
 rdinstreth x29
 # CHECK-INST: csrrs s11, 3200, zero
 # CHECK-ALIAS: rdcycleh s11
 rdcycleh x27
 # CHECK-INST: csrrs t3, 3201, zero
 # CHECK-ALIAS: rdtimeh t3
 rdtimeh x28

test/MC/RISCV/rv32i-valid.s

 # RUN: llvm-mc %s -triple=riscv32 -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc %s -triple riscv64 -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv32 < %s \
 # RUN:     | llvm-objdump -riscv-no-aliases -d -r - \
 # RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv64 < %s \
 # RUN:     | llvm-objdump -riscv-no-aliases -d -r - \
 # RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
 
+.equ CONST, 30
+
 # CHECK-ASM-AND-OBJ: lui a0, 2
 # CHECK-ASM: encoding: [0x37,0x25,0x00,0x00]
 lui a0, 2
 # CHECK-ASM-AND-OBJ: lui s11, 552960
 # CHECK-ASM: encoding: [0xb7,0x0d,0x00,0x87]
 lui s11, (0x87000000>>12)
 # CHECK-ASM-AND-OBJ: lui a0, 0
 # CHECK-ASM: encoding: [0x37,0x05,0x00,0x00]

 # CHECK-ASM-AND-OBJ: lui gp, 0
 # CHECK-ASM: encoding: [0xb7,0x01,0x00,0x00]
 lui gp, 0
 # CHECK-ASM: lui a0, %hi(foo)
 # CHECK-ASM: encoding: [0x37,0bAAAA0101,A,A]
 # CHECK-OBJ: lui a0, 0
 # CHECK-OBJ: R_RISCV_HI20 foo
 lui a0, %hi(foo)
+# CHECK-ASM-AND-OBJ: lui a0, 30
+# CHECK-ASM: encoding: [0x37,0xe5,0x01,0x00]
+lui a0, CONST
 
 # CHECK-ASM-AND-OBJ: auipc a0, 2
 # CHECK-ASM: encoding: [0x17,0x25,0x00,0x00]
 auipc a0, 2
 # CHECK-ASM-AND-OBJ: auipc s11, 552960
 # CHECK-ASM: encoding: [0x97,0x0d,0x00,0x87]
 auipc s11, (0x87000000>>12)
 # CHECK-ASM-AND-OBJ: auipc t0, 1048575
 # CHECK-ASM: encoding: [0x97,0xf2,0xff,0xff]
 auipc t0, 1048575
 # CHECK-ASM-AND-OBJ: auipc gp, 0
 # CHECK-ASM: encoding: [0x97,0x01,0x00,0x00]
 auipc gp, 0
 # CHECK-ASM: auipc a0, %pcrel_hi(foo)
 # CHECK-ASM: encoding: [0x17,0bAAAA0101,A,A]
 # CHECK-OBJ: auipc a0, 0
 # CHECK-OBJ: R_RISCV_PCREL_HI20 foo
 auipc a0, %pcrel_hi(foo)
+# CHECK-ASM-AND-OBJ: auipc a0, 30
+# CHECK-ASM: encoding: [0x17,0xe5,0x01,0x00]
+auipc a0, CONST
 
 # CHECK-ASM-AND-OBJ: jal a2, 1048574
 # CHECK-ASM: encoding: [0x6f,0xf6,0xff,0x7f]
 jal a2, 1048574
 # CHECK-ASM-AND-OBJ: jal a3, 256
 # CHECK-ASM: encoding: [0xef,0x06,0x00,0x10]
 jal a3, 256
 # CHECK-ASM: jal a0, foo
 # CHECK-ASM: encoding: [0x6f,0bAAAA0101,A,A]
 # CHECK-OBJ: jal a0, 0
 # CHECK-OBJ: R_RISCV_JAL foo
 jal a0, foo
 # CHECK-ASM: jal a0, a0
 # CHECK-ASM: encoding: [0x6f,0bAAAA0101,A,A]
 # CHECK-OBJ: jal a0, 0
 # CHECK-OBJ: R_RISCV_JAL a0
 jal a0, a0
+# CHECK-ASM-AND-OBJ: jal a0, 30
+# CHECK-ASM: encoding: [0x6f,0x05,0xe0,0x01]
+jal a0, CONST
 
 # CHECK-ASM-AND-OBJ: jalr a0, a1, -2048
 # CHECK-ASM: encoding: [0x67,0x85,0x05,0x80]
 jalr a0, a1, -2048
 # CHECK-ASM-AND-OBJ: jalr a0, a1, -2048
 # CHECK-ASM: encoding: [0x67,0x85,0x05,0x80]
 jalr a0, a1, %lo(2048)
 # CHECK-ASM-AND-OBJ: jalr t2, t1, 2047
 # CHECK-ASM: encoding: [0xe7,0x03,0xf3,0x7f]
 jalr t2, t1, 2047
 # CHECK-ASM-AND-OBJ: jalr sp, zero, 256
 # CHECK-ASM: encoding: [0x67,0x01,0x00,0x10]
 jalr sp, zero, 256
+# CHECK-ASM-AND-OBJ: jalr a1, a2, 30
+# CHECK-ASM: encoding: [0xe7,0x05,0xe6,0x01]
+jalr a1, a2, CONST
 
 # CHECK-ASM-AND-OBJ: beq s1, s1, 102
 # CHECK-ASM: encoding: [0x63,0x83,0x94,0x06]
 beq s1, s1, 102
 # CHECK-ASM-AND-OBJ: bne a4, a5, -4096
 # CHECK-ASM: encoding: [0x63,0x10,0xf7,0x80]
 bne a4, a5, -4096
 # CHECK-ASM-AND-OBJ: blt sp, gp, 4094
 # CHECK-ASM: encoding: [0xe3,0x4f,0x31,0x7e]
 blt sp, gp, 4094
 # CHECK-ASM-AND-OBJ: bge s2, ra, -224
 # CHECK-ASM: encoding: [0xe3,0x50,0x19,0xf2]
 bge s2, ra, -224
 # CHECK-ASM-AND-OBJ: bltu zero, zero, 0
 # CHECK-ASM: encoding: [0x63,0x60,0x00,0x00]
 bltu zero, zero, 0
 # CHECK-ASM-AND-OBJ: bgeu s8, sp, 512
 # CHECK-ASM: encoding: [0x63,0x70,0x2c,0x20]
 bgeu s8, sp, 512
+# CHECK-ASM-AND-OBJ: bgeu t0, t1, 30
+# CHECK-ASM: encoding: [0x63,0xff,0x62,0x00]
+bgeu t0, t1, CONST
 
 # CHECK-ASM-AND-OBJ: lb s3, 4(ra)
 # CHECK-ASM: encoding: [0x83,0x89,0x40,0x00]
 lb s3, 4(ra)
 # CHECK-ASM-AND-OBJ: lb s3, 4(ra)
 # CHECK-ASM: encoding: [0x83,0x89,0x40,0x00]
 lb s3, +4(ra)
 # CHECK-ASM-AND-OBJ: lh t1, -2048(zero)

 # CHECK-OBJ: lbu s5, 0(s6)
 # CHECK-OBJ: R_RISCV_LO12
 lbu s5, %lo(foo)(s6)
 # CHECK-ASM: lhu t3, %pcrel_lo(foo)(t3)
 # CHECK-ASM: encoding: [0x03,0x5e,0bAAAA1110,A]
 # CHECK-OBJ: lhu t3, 0(t3)
 # CHECK-OBJ: R_RISCV_PCREL_LO12
 lhu t3, %pcrel_lo(foo)(t3)
+# CHECK-ASM-AND-OBJ: lb t0, 30(t1)
+# CHECK-ASM: encoding: [0x83,0x02,0xe3,0x01]
+lb t0, CONST(t1)
 
 # CHECK-ASM-AND-OBJ: sb a0, 2047(a2)
 # CHECK-ASM: encoding: [0xa3,0x0f,0xa6,0x7e]
 sb a0, 2047(a2)
 # CHECK-ASM-AND-OBJ: sh t3, -2048(t5)
 # CHECK-ASM: encoding: [0x23,0x10,0xcf,0x81]
 sh t3, -2048(t5)
 # CHECK-ASM-AND-OBJ: sh t3, -2048(t5)
 # CHECK-ASM: encoding: [0x23,0x10,0xcf,0x81]
 sh t3, %lo(2048)(t5)
 # CHECK-ASM-AND-OBJ: sw ra, 999(zero)
 # CHECK-ASM: encoding: [0xa3,0x23,0x10,0x3e]
 sw ra, 999(zero)
+# CHECK-ASM-AND-OBJ: sw a0, 30(t0)
+# CHECK-ASM: encoding: [0x23,0xaf,0xa2,0x00]
+sw a0, CONST(t0)
 
 # CHECK-ASM-AND-OBJ: addi ra, sp, 2
 # CHECK-ASM: encoding: [0x93,0x00,0x21,0x00]
 addi ra, sp, 2
 # CHECK-ASM: addi ra, sp, %lo(foo)
 # CHECK-ASM: encoding: [0x93,0x00,0bAAAA0001,A]
 # CHECK-OBJ: addi ra, sp, 0
 # CHECK-OBJ: R_RISCV_LO12
 addi ra, sp, %lo(foo)
+# CHECK-ASM-AND-OBJ: addi ra, sp, 30
+# CHECK-ASM: encoding: [0x93,0x00,0xe1,0x01]
+addi ra, sp, CONST
 # CHECK-ASM-AND-OBJ: slti a0, a2, -20
 # CHECK-ASM: encoding: [0x13,0x25,0xc6,0xfe]
 slti a0, a2, -20
 # CHECK-ASM-AND-OBJ: sltiu s2, s3, 80
 # CHECK-ASM: encoding: [0x13,0xb9,0x09,0x05]
 sltiu s2, s3, 0x50
 # CHECK-ASM-AND-OBJ: xori tp, t1, -99
 # CHECK-ASM: encoding: [0x13,0x42,0xd3,0xf9]

 # CHECK-ASM: encoding: [0x13,0x1e,0xfe,0x01]
 slli t3, t3, 31
 # CHECK-ASM-AND-OBJ: srli a0, a4, 0
 # CHECK-ASM: encoding: [0x13,0x55,0x07,0x00]
 srli a0, a4, 0
 # CHECK-ASM-AND-OBJ: srai a2, sp, 15
 # CHECK-ASM: encoding: [0x13,0x56,0xf1,0x40]
 srai a2, sp, 15
+# CHECK-ASM-AND-OBJ: slli t3, t3, 30
+# CHECK-ASM: encoding: [0x13,0x1e,0xee,0x01]
+slli t3, t3, CONST
 
 # CHECK-ASM-AND-OBJ: add ra, zero, zero
 # CHECK-ASM: encoding: [0xb3,0x00,0x00,0x00]
 add ra, zero, zero
 # CHECK-ASM-AND-OBJ: add ra, zero, zero
 # CHECK-ASM: encoding: [0xb3,0x00,0x00,0x00]
 add x1, x0, x0
 # CHECK-ASM-AND-OBJ: sub t0, t2, t1

 
 # CHECK-ASM-AND-OBJ: ecall
 # CHECK-ASM: encoding: [0x73,0x00,0x00,0x00]
 ecall
 # CHECK-ASM-AND-OBJ: ebreak
 # CHECK-ASM: encoding: [0x73,0x00,0x10,0x00]
 ebreak
 
+.equ CONST, 16
+
 # CHECK-ASM-AND-OBJ: csrrw t0, 4095, t1
 # CHECK-ASM: encoding: [0xf3,0x12,0xf3,0xff]
 csrrw t0, 0xfff, t1
 # CHECK-ASM-AND-OBJ: csrrs s0, 3072, zero
 # CHECK-ASM: encoding: [0x73,0x24,0x00,0xc0]
 csrrs s0, 0xc00, x0
 # CHECK-ASM-AND-OBJ: csrrs s3, 1, s5
 # CHECK-ASM: encoding: [0xf3,0xa9,0x1a,0x00]
 csrrs s3, 0x001, s5
 # CHECK-ASM-AND-OBJ: csrrc sp, 0, ra
 # CHECK-ASM: encoding: [0x73,0xb1,0x00,0x00]
 csrrc sp, 0x000, ra
 # CHECK-ASM-AND-OBJ: csrrwi a5, 0, 0
 # CHECK-ASM: encoding: [0xf3,0x57,0x00,0x00]
 csrrwi a5, 0x000, 0
 # CHECK-ASM-AND-OBJ: csrrsi t2, 4095, 31
 # CHECK-ASM: encoding: [0xf3,0xe3,0xff,0xff]
 csrrsi t2, 0xfff, 31
 # CHECK-ASM-AND-OBJ: csrrci t1, 320, 5
 # CHECK-ASM: encoding: [0x73,0xf3,0x02,0x14]
 csrrci t1, 0x140, 5
+# CHECK-ASM-AND-OBJ: csrrci t1, 16, 16
+# CHECK-ASM: encoding: [0x73,0x73,0x08,0x01]
+csrrci t1, CONST, CONST

test/MC/RISCV/rv64i-aliases-valid.s

 # CHECK-EXPAND: slli t4, t4, 12
 # CHECK-EXPAND: addi t4, t4, 1511
 # CHECK-EXPAND: slli t4, t4, 13
 # CHECK-EXPAND: addi t4, t4, -272
 li t4, 0x123456789abcdef0
 # CHECK-EXPAND: addiw t5, zero, -1
 li t5, 0xFFFFFFFFFFFFFFFF
 
+.equ CONST, 0x123456
+# CHECK-EXPAND: lui a0, 291
+# CHECK-EXPAND: addiw a0, a0, 1110
+li a0, CONST
+
+.equ CONST, 0x654321
+# CHECK-EXPAND: lui a0, 1620
+# CHECK-EXPAND: addiw a0, a0, 801
+li a0, CONST
+
 # CHECK-INST: subw t6, zero, ra
 # CHECK-ALIAS: negw t6, ra
 negw x31, x1
 # CHECK-INST: addiw t6, ra, 0
 # CHECK-ALIAS: sext.w t6, ra
 sext.w x31, x1
 
 # The following aliases are accepted as input but the canonical form

test/MC/RISCV/rv64i-valid.s

 # RUN: llvm-mc %s -triple=riscv64 -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv64 < %s \
 # RUN:     | llvm-objdump -riscv-no-aliases -d -r - \
 # RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
 
+.equ CONST, 31
+
 # CHECK-ASM-AND-OBJ: lwu zero, 4(ra)
 # CHECK-ASM: encoding: [0x03,0xe0,0x40,0x00]
 lwu x0, 4(x1)
 # CHECK-ASM-AND-OBJ: lwu sp, 4(gp)
 # CHECK-ASM: encoding: [0x03,0xe1,0x41,0x00]
 lwu x2, +4(x3)
 # CHECK-ASM-AND-OBJ: lwu tp, -2048(t0)
 # CHECK-ASM: encoding: [0x03,0xe2,0x02,0x80]

 # CHECK-ASM: encoding: [0x13,0x9b,0xdb,0x02]
 slli x22, x23, 45
 # CHECK-ASM-AND-OBJ: srli s8, s9, 0
 # CHECK-ASM: encoding: [0x13,0xdc,0x0c,0x00]
 srli x24, x25, 0
 # CHECK-ASM-AND-OBJ: srai s10, s11, 31
 # CHECK-ASM: encoding: [0x13,0xdd,0xfd,0x41]
 srai x26, x27, 31
+# CHECK-ASM-AND-OBJ: srai s10, s11, 31
+# CHECK-ASM: encoding: [0x13,0xdd,0xfd,0x41]
+srai x26, x27, CONST
 
 # CHECK-ASM-AND-OBJ: addiw t3, t4, -2048
 # CHECK-ASM: encoding: [0x1b,0x8e,0x0e,0x80]
 addiw x28, x29, -2048
 # CHECK-ASM-AND-OBJ: addiw t5, t6, 2047
 # CHECK-ASM: encoding: [0x1b,0x8f,0xff,0x7f]
 addiw x30, x31, 2047
 

 # CHECK-ASM: encoding: [0x1b,0xd3,0xf3,0x01]
 srliw t1, t2, 31
 # CHECK-ASM-AND-OBJ: sraiw s0, s1, 0
 # CHECK-ASM: encoding: [0x1b,0xd4,0x04,0x40]
 sraiw s0, s1, 0
 # CHECK-ASM-AND-OBJ: sraiw a0, a1, 31
 # CHECK-ASM: encoding: [0x1b,0xd5,0xf5,0x41]
 sraiw a0, a1, 31
+# CHECK-ASM-AND-OBJ: sraiw a0, a1, 31
+# CHECK-ASM: encoding: [0x1b,0xd5,0xf5,0x41]
+sraiw a0, a1, CONST
 
 # CHECK-ASM-AND-OBJ: addw a2, a3, a4
 # CHECK-ASM: encoding: [0x3b,0x86,0xe6,0x00]
 addw a2, a3, a4
 # CHECK-ASM-AND-OBJ: addw a5, a6, a7
 # CHECK-ASM: encoding: [0xbb,0x07,0x18,0x01]
 addw a5, a6, a7
 # CHECK-ASM-AND-OBJ: subw s2, s3, s4