https://bugs.llvm.org/show_bug.cgi?id=38153
Bug ID: 38153
Summary: clang should have the ability to generate roundps to
implement std::round
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: brucedaw...@chromium.org
CC: llvm-bugs@lists.llvm.org
As reported in crbug.com/863135, std::round() ends up consuming most of the CPU
time in Chrome's ComputeThumbnailScore. This is because of the overhead of the
function call plus what appears to be an inefficient implementation.
We could optimize every call site based on floating-point tricks that work in
particular circumstances or llvm/clang-cl could generate the SSE 4.1 roundss or
roundps instruction:
http://www.info.univ-angers.fr/~richer/ens/l3info/ao/intel_sse4.pdf
std::round has showed up as a performance problem in Chrome before
(crbug.com/617365) and it would be good to solve it generically rather than
just in specific cases.
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