https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102785
Bug ID: 102785
Summary: [12 Regression] {smul,umul}_highpart changes break
bfin-elf
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: law at gcc dot gnu.org
Target Milestone: ---
This change:
commit 555fa3545efe23393ff21fe0928aa3942e1b90ed (refs/bisect/bad)
Author: Roger Sayle <ro...@nextmovesoftware.com>
Date: Thu Oct 7 15:42:09 2021 +0100
Introduce smul_highpart and umul_highpart RTX for high-part multiplications
This patch introduces new RTX codes to allow the RTL passes and
backends to consistently represent high-part multiplications.
Currently, the RTL used by different backends for expanding
smul<mode>3_highpart and umul<mode>3_highpart varies greatly,
with many but not all choosing to express this something like:
[ ... ]
Is causing execution failures for bfin-elf for this code (taken from the
bfin/builtins tests):
extern void abort (void);
typedef short __v2hi __attribute ((vector_size(4)));
typedef __v2hi fract2x16;
typedef short fract16;
int main ()
{
fract2x16 a, b, t;
fract16 t1, t2;
a = __builtin_bfin_compose_2x16 (0x5000, 0x3000);
b = __builtin_bfin_compose_2x16 (0x4000, 0x2000);
t = __builtin_bfin_dspaddsubsat (a, b);
t1 = __builtin_bfin_extract_hi (t);
t2 = __builtin_bfin_extract_lo (t);
if (t1 != 0x7fff || t2 != 0x1000)
abort ();
return 0;
}
Before the change the source compiled down to something like this at -O2:
_main:
R0.H = 20480;
R1.H = 16384;
R1.L = 8192;
R0.L = 12288;
R0 = R0 +|- R1 (S);
R1.L = R0.H << 0;
R1 = R1.L (X);
R2 = 32767 (X);
[--SP] = RETS;
cc =R1==R2;
SP += -12;
if !cc jump .L2;
R0 = R0.L (X);
R1 = 4096 (X);
cc =R0==R1;
if !cc jump .L2;
SP += 12;
R0 = 0 (X);
RETS = [SP++];
rts;
.L2:
call _abort;
What's important here is there's real code that tests some values and
conditionally returns with zero status or aborts.
After the [su]mul_highpart changes we get:
_main:
[--SP] = RETS; // 36 [c=4 l=2] *pushsi_insn
SP += -12; // 37 [c=4 l=2] addsi3/0
call _abort; // 23 [c=0 l=4] *call_symbol
ie, we unconditionally call abort.
Things start to differ in CSE1. But I haven't really tried to debug it.
Thankfully it should be possible to debug with just a cross compiler..
