search for: fwrapv

...if "i + 10" overflows when using twos complement arithmetic. When this option is in effect any attempt to determine whether an operation on signed numbers will overflow must be written carefully to not actually involve overflow. See also the -fwrapv option. Using -fwrapv means that signed overflow is fully defined: it wraps. When -fwrapv is used, there is no difference between -fstrict-overflow and -fno-strict-overflow. With -fwrapv certain types of overflow are permitted. For example, if the compi...

...=ppc-linux-' >> klcc/klibc.config echo 'KCROSS=' >> klcc/klibc.config echo 'CC=ppc-linux-gcc' >> klcc/klibc.config echo 'LD=ppc-linux-ld' >> klcc/klibc.config echo 'REQFLAGS=-D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=32 -fno-stack-protector -fwrapv -m32 -nostdinc -iwithprefix include -D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=32' >> klcc/klibc.config echo 'OPTFLAGS= -Os' >> klcc/klibc.config echo 'LDFLAGS=-m elf32ppclinux' >> klcc/klibc.config echo 'STRIP=ppc-linux-strip' >> klcc/klibc.con...

On Tue, Aug 20, 2013 at 07:44:39AM +0200, leroy christophe wrote: > > > Find attached two patches I have in order to build klibc 2.0.2 > against kernel 3.8.13 > We had to introduce those patches when going from kernel 3.6 to kernel 3.7 > Hope it helps. > those patches are wrong and again very brittle. just use the way it is described in `make help': A) cd ~/src/linux

...pplications. The trapping behavior > would be a really nice addition, though. > > Has anyone quantified the optimizations afforded by undefined signed > overflow? I'd expect that the benefits are minimal for most codes. On > the other hand I've seen reports that gcc's -fwrapv hurts performance of > gcc output significantly. I'm not sure if that is true. Also, it could > be the case that -fwrapv is implemented poorly. No, it's not implemented badly. We've quantified it's performance before and it hurts about 3-5 without high level loop opts/vecto...

...uot; overflows when using twos complement > arithmetic. When this option is in > effect any attempt to determine whether an operation on > signed numbers will overflow > must be written carefully to not actually involve overflow. > > See also the -fwrapv option. Using -fwrapv means that > signed overflow is fully > defined: it wraps. When -fwrapv is used, there is no > difference between > -fstrict-overflow and -fno-strict-overflow. With -fwrapv > certain types of overflow > are permitted. For...

On Aug 22, 2008, at 9:30 AM, Vikram S. Adve wrote: > In the general case, I think you have to be conservative about this > because programmers may deliberately want this kind of "wraparound" > behavior, e.g., with periodic boundary conditions. But 99.9% of > programs probably don't need that so it would be bad to penalize them > for this corner case. In such a

..., which is perfectly > fine when GEP is assumed to have undefined behavior on overflow, but > is > wrong if GEP is allowed to overflow > with well defined behavior (it wraps). > > Also will can the behavior of GEP be changed depending on llvm-gcc's > -fno-strict-aliasing/-fwrapv/-fno-strict-pointer-overflow flags? Yes. To implement -fwrapv, the front-end can omit any of the no-overflow flags, and choose the wrapping form of GEP, as appropriate. I'm not familiar with -fno-strict-pointer-overflow. Do you mean -fno-strict-overflow? I guess for LLVM that would be equival...

...ice is safe for all applications. The trapping behavior would be a really nice addition, though. Has anyone quantified the optimizations afforded by undefined signed overflow? I'd expect that the benefits are minimal for most codes. On the other hand I've seen reports that gcc's -fwrapv hurts performance of gcc output significantly. I'm not sure if that is true. Also, it could be the case that -fwrapv is implemented poorly. > Does anyone know of any C/C++ programs that require integer overflow > on signed arithmetic (even though it is not strictly allowed by the &gt...

This has come up before, and we just added -fwrapv to work around the problem: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110131/115969.html Are you compiling without -fwrapv? Cameron On May 6, 2013, at 4:55 PM, Shuxin Yang <shuxin.llvm at gmail.com> wrote: > Hi, There: > > Clang fails to compile 254.gap @...

...-gzip' length 136572 bytes (133 Kb) opened URL ================================================== downloaded 133 Kb * installing *source* package &#8216;rpart&#8217; ... ** libs i686-pld-linux-gcc -std=gnu99 -I/usr/lib/R/include -D_FORTIFY_SOURCE=2 -fpic -O2 -fno-strict-aliasing -fwrapv -march=i686 -mtune=pentium4 -gdwarf-2 -g2 -c anova.c -o anova.o i686-pld-linux-gcc -std=gnu99 -I/usr/lib/R/include -D_FORTIFY_SOURCE=2 -fpic -O2 -fno-strict-aliasing -fwrapv -march=i686 -mtune=pentium4 -gdwarf-2 -g2 -c anovapred.c -o anovapred.o . . . usersplit.o xval.o -L/usr/lib/R/lib -lR...

...; fine when GEP is assumed to have undefined behavior on overflow, but >> is >> wrong if GEP is allowed to overflow >> with well defined behavior (it wraps). >> >> Also will can the behavior of GEP be changed depending on llvm-gcc's >> -fno-strict-aliasing/-fwrapv/-fno-strict-pointer-overflow flags? >> > > Yes. To implement -fwrapv, the front-end can omit any of the no-overflow > flags, and choose the wrapping form of GEP, as appropriate. > > I'm not familiar with -fno-strict-pointer-overflow. Do you mean > -fno-strict-overfl...

...T) cmp Ptr) ---> (OFFSET cmp 0), which is perfectly fine when GEP is assumed to have undefined behavior on overflow, but is wrong if GEP is allowed to overflow with well defined behavior (it wraps). Also will can the behavior of GEP be changed depending on llvm-gcc's -fno-strict-aliasing/-fwrapv/-fno-strict-pointer-overflow flags? > Front-ends that do crazy things to pointers may need to use > ptrtoint+arithmetic+inttoptr instead of getelementptr. If the > target-independent properties of getelementptr are needed, the > "getelementptr null" trick may be useful. Will...

Hi, There: Clang fails to compile 254.gap @ CPU2000int suite. The symptom is that executable fail to run with reference input. The root cause is that the compiler mistakenly optimizes expr "x * y / y" into x where the x*y is blindly flagged with nsw without any analysis. The preproceeded code is excerpted bellow: cat -n integer.i --------------------------------- 2361

> > After using 'python sdist', can't you use the tarball (in python/dist) > > in order to create a venv directly? > > I think I will be able to install the python library in the venv using > the tarball. However, won't my liguestfs application require some of > the binaries installed as part of 'make install' for running? I am > trying to not

Hi, I am trying to compile the version on rhel 5.x box. Nasm version 0.98.39 I extracted the tar.gz and ran make in the extracted directory. Here is where it stops. gcc -Wp,-MT,rawcon.o,-MD,./.rawcon.o.d -m32 -ffreestanding -fno-stack-protector -fwrapv -freg-struct-return -march=i386 -Os -fomit-frame-pointer -mregparm=3 -DREGPARM=3 -msoft-float -fno-exceptions -fno-asynchronous-unwind-tables -fno-strict-aliasing -falign-functions=0 -falign-jumps=0 -falign-labels=0 -falign-loops=0 -mpreferred-stack-boundary=2 -mincoming-stack-boundary=2 -fvisibili...

...omplex for no additional value. > > The current project is not based in evidence, I have asked for any SPEC benchmark > that shows performance gain by the compiler taking advantage of “undefined behavior” > and no one can show that. > > One easy way to measure this is to enable -fwrapv/-ftrapv on the compiler command line, which impede the compiler's usual exploitation of signed wrap UB in C. Last I heard, those options lead to substantial performance regressions. > In my other emails I point out that Dan achieved the goal of hoisting sign-extension out of loops for LP64...

I use OpenSSH server on an embedded arm using GCC7 cross toolchain. I found that spamming connection attempts sometimes causes aborts in sshd. Upon getting this up in gdb I found that the pointer subtraction inside openbsd-compat/{strlcat.c,strlcpy.c} (and maybe elsewhere) causes the 32 bit pointer difference to wrap which triggers the abort because of the -ftrapv option. This example illustrates

...libc/../include -Iusr/klibc/../include -I/build/buildd/klibc-1.5.20/usr/include -Iusr/include -I/build/buildd/klibc-1.5.20/linux/include -Ilinux/include -I/build/buildd/klibc-1.5.20/linux/arch/arm/include -Ilinux/arch/arm/include -D__KLIBC__=1 -D__KLIBC_MINOR__=5 -D_BITSIZE=32 -fno-stack-protector -fwrapv -fno-exceptions -mabi=aapcs-linux -mno-thumb-interwork -Os -march=armv4 -mtune=strongarm -W -Wall -Wno-sign-compare -Wno-unused-parameter -D__ASSEMBLY__ -nostdinc -iwithprefix include -I/build/buildd/klibc-1.5.20/usr/include/arch/arm -Iusr/include/arch/arm -I/build/buildd/klibc-1.5.20/usr/include/b...

Edwin was asking about how we should handle PR3328, how we should make GEP respect -fwrapv etc. I wrote up some thoughts here if anyone is interested: http://nondot.org/sabre/LLVMNotes/IntegerOverflow.txt -Chris

> before and it hurts about 3-5 without high level loop > opts/vectorization on. With them on, they do roughly nothing in the > presence of -fwrapv because you can't determine bounds of any non > trivial loop. Very interesting, thanks! Before hearing this I'd have said that Java-style overflow is the right language design, but if this makes loop optimizations impossible that is not so good. John