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* [DAGCombine] (float)((int) f) --> ftrunc (PR36617)Sanjay Patel2018-04-201-0/+42
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This was originally committed at rL328921 and reverted at rL329920 to investigate failures in Chrome. This time I've added to the ReleaseNotes to warn users of the potential of exposing UB and let me repeat that here for more exposure: Optimization of floating-point casts is improved. This may cause surprising results for code that is relying on undefined behavior. Code sanitizers can be used to detect affected patterns such as this: int main() { float x = 4294967296.0f; x = (float)((int)x); printf("junk in the ftrunc: %f\n", x); return 0; } $ clang -O1 ftrunc.c -fsanitize=undefined ; ./a.out ftrunc.c:5:15: runtime error: 4.29497e+09 is outside the range of representable values of type 'int' junk in the ftrunc: 0.000000 Original commit message: fptosi / fptoui round towards zero, and that's the same behavior as ISD::FTRUNC, so replace a pair of casts with the equivalent node. We don't have to account for special cases (NaN, INF) because out-of-range casts are undefined. Differential Revision: https://reviews.llvm.org/D44909 llvm-svn: 330437
* revert r328921 - [DAGCombine] (float)((int) f) --> ftrunc (PR36617)Sanjay Patel2018-04-121-42/+0
| | | | | | | This change is exposing UB in source code - as was warned/predicted. :) See D44909 for discussion. Reverting while we figure out how to fix things. llvm-svn: 329920
* [DAGCombine] (float)((int) f) --> ftrunc (PR36617)Sanjay Patel2018-03-311-0/+42
fptosi / fptoui round towards zero, and that's the same behavior as ISD::FTRUNC, so replace a pair of casts with the equivalent node. We don't have to account for special cases (NaN, INF) because out-of-range casts are undefined. Differential Revision: https://reviews.llvm.org/D44909 llvm-svn: 328921
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