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When `objc_direct` methods were implemented, the implicit `_cmd` parameter was left as an argument to the method implementation function, but was unset by callers; if the method body referenced the `_cmd` variable, a selector load would be emitted inside the body. However, this leaves an unused argument in the ABI, and is unnecessary. This change removes the empty/unset argument, and if `_cmd` is referenced inside an `objc_direct` method it will emit local storage for the implicit variable. From the ABI perspective, `objc_direct` methods will have the implicit `self` parameter, immediately followed by whatever explicit arguments are defined on the method, rather than having one unset/undefined register in the middle. Differential Revision: https://reviews.llvm.org/D131424
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! //===---------------------------------------------------------------------===//