| Issue |
134305
|
| Summary |
[LSR] Seemingly incorrect folding
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ashermancinelli
|
https://godbolt.org/z/3834noxac
You can link and run this test if you have the fortran runtime built (`flang test.ll` before and after LSR). The essence is that we convert from i64->fp128->i64 and check that the round trip was exact, and if not, abort with failure message.
```
;; before
3: ; preds = %16, %0
%.014 = phi i64 [ 100, %0 ], [ %17, %16 ]
%.0913 = phi i64 [ 9223372026854775807, %0 ], [ %18, %16 ]
; When this is an sitofp, loop-reduce doesn't do anything weird
%4 = uitofp i64 %.0913 to fp128
%5 = tail call i64 @llvm.fptosi.sat.i64.f128(fp128 %4)
%.not = icmp eq i64 %5, %.0913
br i1 %.not, label %12, label %6
;; after
3: ; preds = %16, %0
%lsr.iv1 = phi i64 [ %lsr.iv.next2, %16 ], [ 9223372026954775807, %0 ]
%lsr.iv = phi i64 [ %lsr.iv.next, %16 ], [ -100, %0 ]
%IV.S. = phi fp128 [ 0xL7000000000000000403DFFFFFFF6AFD0, %0 ], [ %IV.S.next., %16 ]
%4 = add i64 %lsr.iv1, -100000000
%5 = tail call i64 @llvm.fptosi.sat.i64.f128(fp128 %IV.S.)
%.not = icmp eq i64 %4, %5
br i1 %.not, label %13, label %split
```
With a little libquadmath test program, it looks like `0xL7000000000000000403DFFFFFFF6AFD0` is one greater than `%4`, which causes this test to fail.
```
9223372026954775807 | %lsr.iv1 on entry
-100000000 |
------------------- |
9223372026854775807 | %4
|
9223372026854775808 | this hex value converted to int
| 0xL7000000000000000403DFFFFFFF6AFD0
```
---
Extra context: In the IR flang outputs directly after lowering from mlir, the int to float conversion is an `sitofp` instruction, but instcombine changes this to a `uitofp` earlier in the pipeline. If we change the `uitofp` back into an `sitofp` in the godbolt then we get a passing test again.
This is the Fortran source:
```
real(kind=16) dd, lowest, highest
integer(kind=8) :: i, incr, big
integer :: n = 100
incr = 100000000_8
do i = huge(i) - 10000000000_8,huge(i)-incr,incr
if (int(real(i,kind=16),kind=8).ne.i) then
print *,i,real(i,kind=16),int(real(i,kind=16),kind=8)
stop 'FAIL'
endif
enddo
print *,'ok'
end
```
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