Regehr: GCC 4.8 Breaks Broken SPEC 2006 Benchmarks [LWN.net]

Regehr: GCC 4.8 Breaks Broken SPEC 2006 Benchmarks

Posted Mar 25, 2013 13:41 UTC (Mon) by dlthomas (guest, #89935)
In reply to: Regehr: GCC 4.8 Breaks Broken SPEC 2006 Benchmarks by proski
Parent article: Regehr: GCC 4.8 Breaks Broken SPEC 2006 Benchmarks

It's not constraining the lookup, which would make valgrind miss it, but constraining its later assumptions about the variable.

int d[16];

d[k] = 10; /*A*/

if(/*B*/ k < 16) {
...
}

The idea is that when it hits A, if that expression would be false, behavior is already undefined because of what happened at B, so let's optimize for the case that didn't segfault (or corrupt data).

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