http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
Summary: -Wsuggest-attribute=pure makes obviously-incorrect suggestion Product: gcc Version: 4.6.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassig...@gcc.gnu.org ReportedBy: egg...@gnu.org Created attachment 24948 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24948 v.i - input that causes GCC to generate incorrect warning I ran into this problem when building coreutils (git master) using GCC 4.6.1, x86-64, on Fedora 14. For the attached program v.i, "gcc -Wsuggest-attribute=pure -O2 -S v.i" says: v.i:3546:1: warning: function might be candidate for attribute 'pure' if it is known to return normally [-Wsuggest-attribute=pure] But the function in question is obviously not pure: static void advance (_Bool f) { ++pos; if (f && pos >= argc) beyond (); } as it starts off with a side effect (adding 1 to the static variable 'pos'). Here's the output of "gcc -v -save-temps -Wsuggest-attribute=pure -O2 -S v.i": Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-4.6.1/configure --prefix=/home/eggert/opt/Linux-x86_64/gcc-4.6.1 --disable-nls Thread model: posix gcc version 4.6.1 (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wsuggest-attribute=pure' '-O2' '-S' '-mtune=generic' '-march=x86-64' /home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/cc1 -fpreprocessed v.i -quiet -dumpbase v.i -mtune=generic -march=x86-64 -auxbase v -O2 -Wsuggest-attribute=pure -version -o v.s GNU C (GCC) version 4.6.1 (x86_64-unknown-linux-gnu) compiled by GNU C version 4.6.1, GMP version 4.3.1, MPFR version 2.4.2, MPC version 0.8.1 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C (GCC) version 4.6.1 (x86_64-unknown-linux-gnu) compiled by GNU C version 4.6.1, GMP version 4.3.1, MPFR version 2.4.2, MPC version 0.8.1 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: b0a4f47793c670c0e36c6193e4fd175b v.i:3546:1: warning: function might be candidate for attribute 'pure' if it is known to return normally [-Wsuggest-attribute=pure] COMPILER_PATH=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/ LIBRARY_PATH=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wsuggest-attribute=pure' '-O2' '-S' '-mtune=generic' '-march=x86-64'