Instead of passing the pointer to the variable itself a pointer to a temporary
holding the address of the variable is used.
$ cat wait.c
typedef union
{
union wait *__uptr;
int *__iptr;
} __WAIT_STATUS __attribute__ ((__transparent_union__));
union wait
{
int w_status;
};
int wait (__WAIT_STATUS __status_loc);
int do_wait (void) { int status; wait (&status); return status; }
$ gcc -O2 -S -fverbose-asm wait.c
$ cat wait.s
.file "wait.c"
# rs6000/powerpc options: -msdata=data -G 8
# GNU C version 4.1.0 20051001 (experimental) (SUSE Linux)
(powerpc64-suse-linux)
# compiled by GNU C version 4.1.0 20051001 (experimental) (SUSE Linux).
# GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
# options passed: -iprefix -isystem -D__unix__ -D__gnu_linux__
# -D__linux__ -Dunix -D__unix -Dlinux -D__linux -Asystem=linux
# -Asystem=unix -Asystem=posix -auxbase -O2 -fverbose-asm
# options enabled: -falign-loops -fargument-alias -fbranch-count-reg
# -fcaller-saves -fcommon -fcprop-registers -fcrossjumping
# -fcse-follow-jumps -fcse-skip-blocks -fdefer-pop
# -fdelete-null-pointer-checks -fearly-inlining
# -feliminate-unused-debug-types -fexpensive-optimizations -ffunction-cse
# -fgcse -fgcse-lm -fguess-branch-probability -fident -fif-conversion
# -fif-conversion2 -finline-functions-called-once -fipa-pure-const
# -fipa-reference -fipa-type-escape -fivopts -fkeep-static-consts
# -fleading-underscore -floop-optimize -floop-optimize2 -fmath-errno
# -fmerge-constants -fomit-frame-pointer -foptimize-register-move
# -foptimize-sibling-calls -fpeephole -fpeephole2 -freg-struct-return
# -fregmove -freorder-blocks -freorder-functions -frerun-cse-after-loop
# -frerun-loop-opt -fsched-interblock -fsched-spec
# -fsched-stalled-insns-dep -fschedule-insns -fschedule-insns2
# -fshow-column -fsplit-ivs-in-unroller -fstrength-reduce
# -fstrict-aliasing -fthread-jumps -ftrapping-math -ftree-ccp -ftree-ch
# -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts
# -ftree-dse -ftree-fre -ftree-loop-im -ftree-loop-ivcanon
# -ftree-loop-optimize -ftree-lrs -ftree-pre -ftree-salias -ftree-sink
# -ftree-sra -ftree-store-ccp -ftree-store-copy-prop -ftree-ter
# -ftree-vect-loop-version -ftree-vrp -funit-at-a-time -fverbose-asm
# -fzero-initialized-in-bss -m32 -maix-struct-return -mbig -mbig-endian
# -mbss-plt -mfp-in-toc -mfused-madd -mhard-float -mnew-mnemonics
# -mpowerpc -msched-prolog -mupdate
# Compiler executable checksum: 98247ca61e462f7c754c17f0242fef41
.section ".text"
.align 2
.p2align 4,,15
.globl do_wait
.type do_wait, @function
do_wait:
mflr 0 #,
stwu 1,-32(1) #,,
stw 0,36(1) #,
addi 3,1,24 #,,
addi 0,1,8 # status.1,,
stw 0,24(1) #, status.1
bl wait #
lwz 0,36(1) #,
lwz 3,8(1) # status, <result>
addi 1,1,32 #,,
mtlr 0 #,
blr #
.size do_wait,.-do_wait
.ident "GCC: (GNU) 4.1.0 20051001 (experimental) (SUSE Linux)"
.section .note.GNU-stack,"",@progbits
--
Summary: [4.1 regression] __transparent_union__ mishandled
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: schwab at suse dot de
GCC target triplet: powerpc-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24255
