This was reported over on the older gcc@ list. Essentially the soft-float code for m68k mis-handles the sign bit for 32bit floating point addition when one or both arguments is infinity. Essentially we try to extract the sign bit from a saved copy of the input value. However we saved the input value *after* its sign bit had already been cleared. Fixing is pretty easy -- we just need to move the save point earlier.
64bit floating point appears to handle this correctly. I seriously considered mirroring how the 64bit path handles this situation but that was going to require a bit more surgery and given the lack of testing infrastructure for m68k soft-float the risk/reward didn't seem worth it to me. Installed on the trunk. Jeff
diff --git a/libgcc/ChangeLog b/libgcc/ChangeLog index e8886cfda77..1b24190cf30 100644 --- a/libgcc/ChangeLog +++ b/libgcc/ChangeLog @@ -1,3 +1,8 @@ +2018-05-23 Kalamatee <kalama...@gmail.com> + + * config/m68k/lb1sf68.S (Laddsf$nf): Fix sign bit handling in + path to Lf$finfty. + 2018-05-18 Kito Cheng <kito.ch...@gmail.com> Monk Chiang <sh.chian...@gmail.com> Jim Wilson <j...@sifive.com> diff --git a/libgcc/config/m68k/lb1sf68.S b/libgcc/config/m68k/lb1sf68.S index 1d9392a4ef7..325a7c17d9b 100644 --- a/libgcc/config/m68k/lb1sf68.S +++ b/libgcc/config/m68k/lb1sf68.S @@ -3111,6 +3111,8 @@ Laddsf$nf: movel a6@(12),d1 | did some processing already) movel IMM (INFINITY),d4 | useful constant (INFINITY) movel d0,d2 | save sign bits + movel d0,d7 | into d7 as well as we may need the sign + | bit before jumping to LfSinfty movel d1,d3 bclr IMM (31),d0 | clear sign bits bclr IMM (31),d1 @@ -3125,7 +3127,6 @@ Laddsf$nf: | are adding or subtracting them. eorl d3,d2 | to check sign bits bmi 1f - movel d0,d7 andl IMM (0x80000000),d7 | get (common) sign bit bra Lf$infty 1: @@ -3135,7 +3136,6 @@ Laddsf$nf: cmpl d1,d0 | are both infinite? beq Lf$inop | if so return NaN - movel d0,d7 andl IMM (0x80000000),d7 | get a's sign bit ' cmpl d4,d0 | test now for infinity beq Lf$infty | if a is INFINITY return with this sign