http://llvm.org/bugs/show_bug.cgi?id=22556
Bug ID: 22556
Summary: placement new null checks should be optimized away
Product: clang
Version: 3.5
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Although the C++ standard address the placement-new/nullptr issue in C++17, it
would seem like the optimizer should be able to optimize away the cost
regardless, at least for vector.
Although placement new could be being called on a nullptr, it will be called
with p[i] where i is some value in [0, size() - 1].
Except for the p[0] case, p[x] where x is in [1, size() - 1] cannot be a
nullptr since pointer arithmetic is undefined behaviour for overflow.
Test-case code:
https://pastebin.mozilla.org/8625250
More information:
http://www.reddit.com/r/cpp/comments/2v3viw/cs_placementnew_prevents_optimalcode_generation/
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