mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-14 21:26:06 +00:00
8c85bca5a5
As discussed in the mail thread <https://groups.google.com/a/isocpp.org/forum/ #!topic/std-discussion/T64_dW3WKUk> "Calling noexcept function throug non- noexcept pointer is undefined behavior?", such a call should not be UB. However, Clang currently warns about it. This change removes exception specifications from the function types recorded for -fsanitize=function, both in the functions themselves and at the call sites. That means that calling a non-noexcept function through a noexcept pointer will also not be flagged as UB. In the review of this change, that was deemed acceptable, at least for now. (See the "TODO" in compiler-rt test/ubsan/TestCases/TypeCheck/Function/function.cpp.) To remove exception specifications from types, the existing internal ASTContext::getFunctionTypeWithExceptionSpec was made public, and some places otherwise unrelated to this change have been adapted to call it, too. This is the cfe part of a patch covering both cfe and compiler-rt. Differential Revision: https://reviews.llvm.org/D40720 llvm-svn: 321859
IRgen optimization opportunities. //===---------------------------------------------------------------------===// The common pattern of -- short x; // or char, etc (x == 10) -- generates an zext/sext of x which can easily be avoided. //===---------------------------------------------------------------------===// Bitfields accesses can be shifted to simplify masking and sign extension. For example, if the bitfield width is 8 and it is appropriately aligned then is is a lot shorter to just load the char directly. //===---------------------------------------------------------------------===// It may be worth avoiding creation of alloca's for formal arguments for the common situation where the argument is never written to or has its address taken. The idea would be to begin generating code by using the argument directly and if its address is taken or it is stored to then generate the alloca and patch up the existing code. In theory, the same optimization could be a win for block local variables as long as the declaration dominates all statements in the block. NOTE: The main case we care about this for is for -O0 -g compile time performance, and in that scenario we will need to emit the alloca anyway currently to emit proper debug info. So this is blocked by being able to emit debug information which refers to an LLVM temporary, not an alloca. //===---------------------------------------------------------------------===// We should try and avoid generating basic blocks which only contain jumps. At -O0, this penalizes us all the way from IRgen (malloc & instruction overhead), all the way down through code generation and assembly time. On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just direct branches! //===---------------------------------------------------------------------===//