SCEV fails to take advantage of nsw

[nlewycky]

Bugzilla Link	11409
Version	trunk
OS	Linux
CC	@atrick

Extended Description

opt -O2 does a pretty decent job of handling this loop:

int f(int i) { int j, k = 0; for (j = i; j < i + 10; ++j) ++k; return k; }

but it's not taking advantage of the no-signed-wrap property. GCC optimizes it straight down to "return 10".

[JOE1994]

LLVM trunk now also optimizes the program straight down to return 10 on x86_64:

• Godbolt link : https://godbolt.org/z/ccsj55q88

[fhahn]

Thanks for checking & closing!