[committed][PATCH] Fix m68k soft float handling of infinity

[Jeff Law]

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