[Bug target/65916] Unnecessary floating-point instruction causes runtime exception on PowerPC

[nikolay.pakulin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65916

--- Comment #2 from Nikolay Pakulin nikolay.pakulin at gmail dot com ---
(In reply to Segher Boessenkool from comment #1)
 GCC 5 does not do this for me.
 
 You need to add -msoft-float if you have no hardware float; doing
 that solves the problem for me (with a GCC 4.7 I had handy).  Does
 that work for you?

Yes, the workaround with -msoft-float works fine.
I din't try GCC 5, therefore I can't say anything.

NP

[Bug c/65916] New: Unnecessary floating-point instruction causes runtime exception on PowerPC

[nikolay.pakulin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65916

Bug ID: 65916
   Summary: Unnecessary floating-point instruction causes runtime
exception on PowerPC
   Product: gcc
   Version: 4.9.1
Status: UNCONFIRMED
  Severity: critical
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: nikolay.pakulin at gmail dot com
  Target Milestone: ---

Created attachment 35412
  -- https://gcc.gnu.org/bugzilla/attachment.cgi?id=35412action=edit
Test case to reproduce the issue

Writing 64-bit integers to memory on 32-bit PPC involves floating point
register FP0.  When floating-point support is disabled (bit FP is cleared in
MSR register) the generated code leads to exception FP unavailable interrupt.

The test case compiled by GCC cross compiler running on x86_64 Linux.

powerpc-elf-gcc -S -m32 -mcpu=e500mc uint64.c


-- uint64.c --
typedef unsigned long long u64;

u64 globvar;

void f(u64 arg) { 
  globvar = arg;
}
-- /uint64.c --

-- Generated ASM --
f:
stwu 1,-32(1)
stw 31,28(1)
mr 31,1
stw 3,8(31) # Copies 'arg' to the temporary on the stack
stw 4,12(31)# 
lis 9,globvar@ha
la 9,globvar@l(9)
lfd 0,8(31) # Loads the temporary to FP0 -- exception!
stfd 0,0(9) # Store FP0 to memory
addi 11,31,32
lwz 31,-4(11)
mr 1,11
blr
-- End of Generated ASM --

== GCC specs ==
Using built-in specs.
COLLECT_GCC=powerpc-elf-gcc
COLLECT_LTO_WRAPPER=/opt/crosstools/powerpc-elf-4.9.1-Linux-x86_64/bin/../libexec/gcc/powerpc-elf/4.9.1/lto-wrapper
Target: powerpc-elf
Configured with: ../gcc-4.9.1/configure --target=powerpc-elf
--prefix=/home/geist/svn/toolchains/powerpc-elf-4.9.1-Linux-x86_64
--enable-languages=c,c++ --disable-werror
Thread model: single
gcc version 4.9.1 (GCC) 
== End of GCC specs ==

The workaround is to compile with optimization turned on. With -O switch GCC
produces ASM without FP0:

powerpc-elf-gcc -S -m32 -mcpu=e500mc -O uint64.c
-- Generated optimized ASM --
f:
lis 9,globvar@ha
la 9,globvar@l(9)
stw 3,0(9)# direct write to the destination
stw 4,4(9)# 
blr
-- End of generated optimized ASM --