https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65740
Bug ID: 65740
Summary: spectacularly bad inlinining decisions with -Os
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: westfw at yahoo dot com
Created attachment 35298
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35298&action=edit
preprocessed source code example.
Compiling a module with 4.8.1 and -Os results in a binary more than triple the
size of compiling the same module with 4.3.2, due to bad decisions about
inlining a function.
Dumping inline debug info (-fdump-ipa-inline) shows that the compiler is coming
up with a negative "badness" for the especially-bad function (move3Servos), and
the number is "suspicious" (0xBFFFFFF8) (without understanding what the badness
is supposed to be.)
Considering void move3Servos(Servo, float, Servo, float, Servo, float, float)
with 87 size
to be inlined into void loop() in oiOSoul.ino:325
Estimated growth after inlined into all is +412 insns.
Estimated badness is -1073741824, frequency 0.01.
Inlined into void loop() which now has time 351 and size 628,net change of +0.
(also not that that was about the 40th call of move3Servos() from loop()
analyzed, each with "growth" ~400 insns, and it now thinks the total size is
628, which is ridiculous.)
Might be a duplicate of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57218
Except that that seems to describe a more trivial and less awful ocurrence.
Originally noticed withing Arduino (avr-g++), but NOT cpu specific, and not C++
specific. The attached example is x86 gcc 4.7.2:
/sw/lib/gcc4.7/bin/gcc-fsf-4.7 -c -Os -w foo.ii -v -saveemps -fdump-ipa-inline
Using built-in specs.
COLLECT_GCC=/sw/lib/gcc4.7/bin/gcc-fsf-4.7
Target: x86_64-apple-darwin11.4.2
Configured with: ../gcc-4.7.2/configure --prefix=/sw --prefix=/sw/lib/gcc4.7
--mandir=/sw/share/man --infodir=/sw/lib/gcc4.7/info
--enable-languages=c,c++,fortran,lto,objc,obj-c++,java --with-gmp=/sw
--with-libiconv-prefix=/sw --with-ppl=/sw --with-cloog=/sw --with-mpc=/sw
--with-system-zlib --x-includes=/usr/X11R6/include --x-libraries=/usr/X11R6/lib
--program-suffix=-fsf-4.7 --enable-cloog-backend=isl
Thread model: posix
gcc version 4.7.2 (GCC)
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.9.4' '-c' '-Os' '-w' '-v'
'-save-temps' '-fdump-ipa-inline' '-mtune=core2'
/sw/lib/gcc4.7/libexec/gcc/x86_64-apple-darwin11.4.2/4.7.2/cc1plus
-fpreprocessed foo.ii -fPIC -quiet -dumpbase foo.ii -mmacosx-version-min=10.9.4
-mtune=core2 -auxbase foo -Os -w -version -fdump-ipa-inline -o foo.s
GNU C++ (GCC) version 4.7.2 (x86_64-apple-darwin11.4.2)
compiled by GNU C version 4.7.2, GMP version 5.1.0, MPFR version 3.1.1,
MPC version 1.0.1
warning: GMP header version 5.1.0 differs from library version 5.1.1.
warning: MPFR header version 3.1.1 differs from library version 3.1.2.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 4.7.2 (x86_64-apple-darwin11.4.2)
compiled by GNU C version 4.7.2, GMP version 5.1.0, MPFR version 3.1.1,
MPC version 1.0.1
warning: GMP header version 5.1.0 differs from library version 5.1.1.
warning: MPFR header version 3.1.1 differs from library version 3.1.2.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 712698abe851e71eccb1a409a1351965
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.9.4' '-c' '-Os' '-w' '-v'
'-save-temps' '-fdump-ipa-inline' '-mtune=core2'
as -arch x86_64 -force_cpusubtype_ALL -o foo.o foo.s
COMPILER_PATH=/sw/lib/gcc4.7/libexec/gcc/x86_64-apple-darwin11.4.2/4.7.2/:/sw/lib/gcc4.7/libexec/gcc/x86_64-apple-darwin11.4.2/4.7.2/:/sw/lib/gcc4.7/libexec/gcc/x86_64-apple-darwin11.4.2/:/sw/lib/gcc4.7/lib/gcc/x86_64-apple-darwin11.4.2/4.7.2/:/sw/lib/gcc4.7/lib/gcc/x86_64-apple-darwin11.4.2/
LIBRARY_PATH=/sw/lib/gcc4.7/lib/gcc/x86_64-apple-darwin11.4.2/4.7.2/:/sw/lib/gcc4.7/lib/gcc/x86_64-apple-darwin11.4.2/4.7.2/../../../:/usr/lib/
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.9.4' '-c' '-Os' '-w' '-v'
'-save-temps' '-fdump-ipa-inline' '-mtune=core2'
BillW-MacOSX-2<10422> size foo.o
__TEXT __DATA __OBJC others dec hex
29936 209 0 0 30145 75c1
#(without inlining)
BillW-MacOSX-2<10423> /sw/lib/gcc4.7/bin/gcc-fsf-4.7 -c -Os -w foo.ii
-fno-inline-small-functions
BillW-MacOSX-2<10424> size foo.o
__TEXT __DATA __OBJC others dec hex
8725 209 0 0 8934 22e6
