John Regehr
tonight I am annoyed by: a program that both gcc and clang compile at -O2 and neither compiles at -O0
easier to arrange than you might think void bar(void); static int x; int main(void) { if (x) bar(); }
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@johnregehr UB b/c x was used before being initialized (unless static vars are special in that respect)? - View other replies
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@cr1901 globals in C are zeroed -
@johnregehr@cr1901 just globals? I thought it was anything with static storage -
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@johnregehr aren't statics zeroed? -
@mrkkrj they are zeroed -
@johnregehr than the mystery is solved -
@mrkkrj it's not a mystery, it's an annoyance
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@johnregehr seems perfectly valid under the as-if rule: http://en.cppreference.com/w/cpp/language/as_if … -
@shafikyaghmour yes, valid but sometimes obnoxious
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@johnregehr You mean that this code doesn't link with -O0?
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@johnregehr undefined behaviour remains undefined? -
@Ferretzau nope, the program is perfectly well defined -
@johnregehr that prgm looked ill defined, assumed when constants assigned, which I thought was not specified, tho Im likely wrong.
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@johnregehr a debug version walks into a bar(). A release version doesn't walk into a bar(). Joke's on you. -
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@fugueish@johnregehr foo.c:(.text+0x1e): undefined reference to `bar'; at -O2 the call gets removed. a surprisingly subtle case! -
@stdlib@johnregehr Even with -Wall -Wextra, no warning about the always-false condition! sigh
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William D. Jones
kragen
marek krajewski
Shafik Yaghmour
Jens Gustedt
Ferretz
JF Bastien
Chris Palmer
austin seipp
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