forked from OSchip/llvm-project
9971a6841c
See PR25822 for a more full summary, but we were conflating the concepts of "capture" and "escape". We were proving nocapture and using that proof to infer noescape, which is not true. Escaped-ness is a function-local property - as soon as a value is used in a call argument it escapes. Capturedness is a related but distinct property. It implies a *temporally limited* escape. Consider:
static int a;
int b;
int g(int * nocapture arg);
int f() {
a = 2; // Even though a escapes to g, it is not captured so can be treated as non-escaping here.
g(&a); // But here it must be treated as escaping.
g(&b); // Now that g(&a) has returned we know it was not captured so we can treat it as non-escaping again.
}
The original commit did not sufficiently understand this nuance and so caused PR25822 and PR26046.
r248576 included both a performance improvement (which has been backed out) and a related conformance fix (which has been kept along with its testcase).
llvm-svn: 257058
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| .. | ||
| 2008-09-03-ReadGlobals.ll | ||
| aliastest.ll | ||
| atomic-instrs.ll | ||
| chaining-analysis.ll | ||
| inaccessiblememonly.ll | ||
| indirect-global.ll | ||
| memset-escape.ll | ||
| modreftest.ll | ||
| nonescaping-noalias.ll | ||
| pr12351.ll | ||
| pr25309.ll | ||
| purecse.ll | ||
| volatile-instrs.ll | ||
| weak-interposition.ll | ||