[llvm-bugs] [Bug 32713] New: mips/mipsel i128 sub/add generates wrong code

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=32713

            Bug ID: 32713
           Summary: mips/mipsel i128 sub/add generates wrong code
           Product: libraries
           Version: 3.9
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: MIPS
          Assignee: unassignedbugs at nondot.org
          Reporter: simonas+llvm.org at kazlauskas.me
                CC: llvm-bugs at lists.llvm.org

i128 subtraction on 32bit MIPSes seems to fail to propagate the carry bit from
lower 64 bits to higher 64 bits.

Therefore on x86(_64) the foo function from IR below returns `~0` (i128 with
all bits set), whereas on MIPS it returns something like
0000_0000_0000_0000_ffff_ffff_ffff_ffff.

`add i128 %a, %b` where `%a = i128 -1` and `%b = i128 1` seems to also not
produce `0` as a result.

Reproduction IR (subtraction):

target datalayout = "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64"
target triple = "mipsel-unknown-linux-gnu"

define i128 @foo(i128, i128) unnamed_addr #0 {
start:
  %a = sub i128 %0, %1
  ret i128 %a
}

define i32 @main(i32, i8**) unnamed_addr {
start:
  %r = tail call i128 @foo(i128 0, i128 1)
  %c = icmp ne i128 %r, -1
  %x = zext i1 %c to i32
  ret i32 %x
}

attributes #0 = { norecurse nounwind readnone uwtable noinline }

!llvm.module.flags = !{!0}
!0 = !{i32 1, !"PIE Level", i32 2}

Reproduction IR (addition): 

target datalayout = "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64"
target triple = "mipsel-unknown-linux-gnu"

define i128 @foo(i128, i128) unnamed_addr #0 {
start:
  %a = add i128 %0, %1
  ret i128 %a
}

define i32 @main(i32, i8**) unnamed_addr {
start:
  %r = tail call i128 @foo(i128 -1, i128 1)
  %c = icmp ne i128 %r, 0
  %x = zext i1 %c to i32
  ret i32 %x
}

attributes #0 = { norecurse nounwind readnone uwtable noinline }

!llvm.module.flags = !{!0}
!0 = !{i32 1, !"PIE Level", i32 2}

Testing procedure:

llc file.ll -filetype=obj && cc file.o && ./a.out && echo "success"

LLVM Version:

3.9.1. Do not have 4.0 handy to test with it.

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