[RISCV] PseudoVCPOP_M_B8_MASK transforms into incorrect machine code after RISCVVectorPeephole

[BeMg]

https://godbolt.org/z/4sxvzGoPG

#include <iostream>
#include <riscv_vector.h>
using std::cerr;
using std::endl;
template <class T> bool __attribute__((noinline)) check(T, T) {}
unsigned long main_var_59;
int main() {
  unsigned long var_61;
  vbool8_t var_8 = __riscv_vmset_m_b8(7);
  unsigned long var_5 = __riscv_vcpop_m_b8_m(var_8, var_8, 6);
  vbool8_t var_19;
  if (check(var_5, var_61))
    cerr << endl;
  unsigned long var_4 = __riscv_vcpop_m_b8_m(var_8, var_19, 8);
  check(var_4, main_var_59);
}

# After RISC-V Vector Peephole Optimization
# Machine code for function main: IsSSA, TracksLiveness

...
*** Bad machine code: Too few operands ***
- function:    main
- basic block: %bb.7  (0x411b1a70)
- instruction: %20:gpr = PseudoVCPOP_M_B8 8, 0, debug-location !1042; example.cpp:14:25
4 operands expected, but 3 given.

*** Bad machine code: Expected a register operand. ***
- function:    main
- basic block: %bb.7  (0x411b1a70)
- instruction: %20:gpr = PseudoVCPOP_M_B8 8, 0, debug-location !1042; example.cpp:14:25
- operand 1:   8

Maybe this line

llvm-project/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp

Line 486 in 82d5dd2

MI.removeOperand(PassthruOpIdx);

which comes from 1294407 is reason.

[BeMg]

cc @lukel97 @preames

[llvmbot]

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

Author: Piyou Chen (BeMg)

https://godbolt.org/z/4sxvzGoPG

#include <iostream>
#include <riscv_vector.h>
using std::cerr;
using std::endl;
template <class T> bool __attribute__((noinline)) check(T, T) {}
unsigned long main_var_59;
int main() {
  unsigned long var_61;
  vbool8_t var_8 = __riscv_vmset_m_b8(7);
  unsigned long var_5 = __riscv_vcpop_m_b8_m(var_8, var_8, 6);
  vbool8_t var_19;
  if (check(var_5, var_61))
    cerr << endl;
  unsigned long var_4 = __riscv_vcpop_m_b8_m(var_8, var_19, 8);
  check(var_4, main_var_59);
}

# After RISC-V Vector Peephole Optimization
# Machine code for function main: IsSSA, TracksLiveness

...
*** Bad machine code: Too few operands ***
- function:    main
- basic block: %bb.7  (0x411b1a70)
- instruction: %20:gpr = PseudoVCPOP_M_B8 8, 0, debug-location !1042; example.cpp:14:25
4 operands expected, but 3 given.

*** Bad machine code: Expected a register operand. ***
- function:    main
- basic block: %bb.7  (0x411b1a70)
- instruction: %20:gpr = PseudoVCPOP_M_B8 8, 0, debug-location !1042; example.cpp:14:25
- operand 1:   8

Maybe this line

llvm-project/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp

Line 486 in 82d5dd2

MI.removeOperand(PassthruOpIdx);

which comes from 1294407 is reason.