[llvm] [RISCV] Only allow 5 bit shift amounts in disassembler for RV32. (PR #115432)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

Fixes 2 old TODOs

---
Full diff: https://github.com/llvm/llvm-project/pull/115432.diff


4 Files Affected:

- (modified) llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp (+22) 
- (modified) llvm/lib/Target/RISCV/RISCVInstrInfo.td (+1-2) 
- (modified) llvm/lib/Target/RISCV/RISCVInstrInfoC.td (+1-2) 
- (added) llvm/test/MC/Disassembler/RISCV/rv32-invalid-shift.txt (+10) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index be0a61263297e4..d985b45495864a 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -314,6 +314,20 @@ static DecodeStatus decodeUImmOperand(MCInst &Inst, uint32_t Imm,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus decodeUImmLog2XLenOperand(MCInst &Inst, uint32_t Imm,
+                                              int64_t Address,
+                                              const MCDisassembler *Decoder) {
+  assert(isUInt<6>(Imm) && "Invalid immediate");
+
+  if (!Decoder->getSubtargetInfo().hasFeature(RISCV::Feature64Bit) &&
+      !isUInt<5>(Imm))
+    return MCDisassembler::Fail;
+  ;
+
+  Inst.addOperand(MCOperand::createImm(Imm));
+  return MCDisassembler::Success;
+}
+
 template <unsigned N>
 static DecodeStatus decodeUImmNonZeroOperand(MCInst &Inst, uint32_t Imm,
                                              int64_t Address,
@@ -323,6 +337,14 @@ static DecodeStatus decodeUImmNonZeroOperand(MCInst &Inst, uint32_t Imm,
   return decodeUImmOperand<N>(Inst, Imm, Address, Decoder);
 }
 
+static DecodeStatus
+decodeUImmLog2XLenNonZeroOperand(MCInst &Inst, uint32_t Imm, int64_t Address,
+                                 const MCDisassembler *Decoder) {
+  if (Imm == 0)
+    return MCDisassembler::Fail;
+  return decodeUImmLog2XLenOperand(Inst, Imm, Address, Decoder);
+}
+
 template <unsigned N>
 static DecodeStatus decodeSImmOperand(MCInst &Inst, uint32_t Imm,
                                       int64_t Address,
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.td b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
index a867368235584c..1908f5e5dede85 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
@@ -201,8 +201,7 @@ def uimmlog2xlen : RISCVOp, ImmLeaf<XLenVT, [{
   return isUInt<5>(Imm);
 }]> {
   let ParserMatchClass = UImmLog2XLenAsmOperand;
-  // TODO: should ensure invalid shamt is rejected when decoding.
-  let DecoderMethod = "decodeUImmOperand<6>";
+  let DecoderMethod = "decodeUImmLog2XLenOperand";
   let MCOperandPredicate = [{
     int64_t Imm;
     if (!MCOp.evaluateAsConstantImm(Imm))
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoC.td b/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
index 8a76dba23d42a7..e5a5f60f9fec10 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
@@ -24,8 +24,7 @@ def uimmlog2xlennonzero : RISCVOp, ImmLeaf<XLenVT, [{
   return isUInt<5>(Imm) && (Imm != 0);
 }]> {
   let ParserMatchClass = UImmLog2XLenNonZeroAsmOperand;
-  // TODO: should ensure invalid shamt is rejected when decoding.
-  let DecoderMethod = "decodeUImmNonZeroOperand<6>";
+  let DecoderMethod = "decodeUImmLog2XLenNonZeroOperand";
   let OperandType = "OPERAND_UIMMLOG2XLEN_NONZERO";
   let MCOperandPredicate = [{
     int64_t Imm;
diff --git a/llvm/test/MC/Disassembler/RISCV/rv32-invalid-shift.txt b/llvm/test/MC/Disassembler/RISCV/rv32-invalid-shift.txt
new file mode 100644
index 00000000000000..f56530190adc81
--- /dev/null
+++ b/llvm/test/MC/Disassembler/RISCV/rv32-invalid-shift.txt
@@ -0,0 +1,10 @@
+# RUN: not llvm-mc -disassemble -triple=riscv32 -mattr=+c < %s 2>&1 | FileCheck %s --check-prefix=RV32
+# RUN: llvm-mc -disassemble -triple=riscv64 -mattr=+c < %s 2>&1 | FileCheck %s --check-prefix=RV64
+
+[0x13,0x9b,0xdb,0x02]
+# RV32: warning: invalid instruction encoding
+# RV64: slli    s6, s7, 45
+
+[0xfd,0x92]
+# RV32: warning: invalid instruction encoding
+# RV64: srli    a3, a3, 63

``````````

</details>


https://github.com/llvm/llvm-project/pull/115432