[flang-commits] [flang] [flang] Eliminate workaround for optimizing maxval Fortran intrinsic (PR #65814)

[Slava Zakharin via flang-commits]

vzakhari wrote:

Yes, it might be a bit complex to properly check this.

Please try this:
```
subroutine test(x, t)
  real(16) :: x(100), t
  t = maxval(x)
end subroutine test
```

`flang-new -O2 -ffast-math -c maxval.f90`:
```
LLVM ERROR: Cannot select: t27: f128 = fmaximum nnan ninf nsz arcp contract afn reassoc t26, t25
  t26: f128,ch = load<(load (s128) from %ir.scevgep, !tbaa !3)> t0, t5, undef:i64
    t5: i64 = add t2, t4
      t2: i64,ch = CopyFromReg t0, Register:i64 %4
        t1: i64 = Register %4
      t4: i64,ch = CopyFromReg t0, Register:i64 %0
        t3: i64 = Register %0
    t9: i64 = undef
  t25: f128 = fmaximum nnan ninf nsz arcp contract afn reassoc t24, t21
    t24: f128,ch = load<(load (s128) from %ir.scevgep2, !tbaa !3)> t0, t23, undef:i64
      t23: i64 = add t5, Constant:i64<-16>
        t5: i64 = add t2, t4
          t2: i64,ch = CopyFromReg t0, Register:i64 %4
            t1: i64 = Register %4
          t4: i64,ch = CopyFromReg t0, Register:i64 %0
            t3: i64 = Register %0
        t22: i64 = Constant<-16>
      t9: i64 = undef
    t21: f128 = fmaximum nnan ninf nsz arcp contract afn reassoc t20, t17
      t20: f128,ch = load<(load (s128) from %ir.scevgep4, !tbaa !3)> t0, t19, undef:i64
        t19: i64 = add t5, Constant:i64<-32>
          t5: i64 = add t2, t4
            t2: i64,ch = CopyFromReg t0, Register:i64 %4
              t1: i64 = Register %4
            t4: i64,ch = CopyFromReg t0, Register:i64 %0
              t3: i64 = Register %0
          t18: i64 = Constant<-32>
        t9: i64 = undef
      t17: f128 = fmaximum nnan ninf nsz arcp contract afn reassoc t16, t13
        t16: f128,ch = load<(load (s128) from %ir.scevgep6, !tbaa !3)> t0, t15, undef:i64
          t15: i64 = add t5, Constant:i64<-48>
            t5: i64 = add t2, t4
              t2: i64,ch = CopyFromReg t0, Register:i64 %4
                t1: i64 = Register %4
              t4: i64,ch = CopyFromReg t0, Register:i64 %0
                t3: i64 = Register %0
            t14: i64 = Constant<-48>
          t9: i64 = undef
        t13: f128 = fmaximum nnan ninf nsz arcp contract afn reassoc t10, t12
          t10: f128,ch = load<(load (s128) from %ir.scevgep8, !tbaa !3)> t0, t7, undef:i64
            t7: i64 = add t5, Constant:i64<-64>
              t5: i64 = add t2, t4
                t2: i64,ch = CopyFromReg t0, Register:i64 %4
                  t1: i64 = Register %4
                t4: i64,ch = CopyFromReg t0, Register:i64 %0
                  t3: i64 = Register %0
              t6: i64 = Constant<-64>
            t9: i64 = undef
          t12: f128,ch = CopyFromReg t0, Register:f128 %1
            t11: f128 = Register %1
In function: test_
```

https://github.com/llvm/llvm-project/pull/65814