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[committed] Fix m68k soft float handling of infinity

Message ID cd7d0de2-2166-8a2e-55a8-5339458b53c9@redhat.com
State New
Headers show
Series [committed] Fix m68k soft float handling of infinity | expand

Commit Message

Jeff Law May 23, 2018, 10:29 p.m. UTC 
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 mbox series

Patch

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  <kalamatee@gmail.com>
+
+	* config/m68k/lb1sf68.S (Laddsf$nf): Fix sign bit handling in
+	path to Lf$finfty.
+
 2018-05-18  Kito Cheng <kito.cheng@gmail.com>
 	    Monk Chiang  <sh.chiang04@gmail.com>
 	    Jim Wilson <jimw@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