mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-10 17:36:07 +00:00
86aba5eeee
Thunks that return member pointers via sret are broken due to using temporary storage for the return value on the stack and then passing that pointer to a tail call, violating the rule that a tail call can't access allocas in the caller (see bug). Since r90526, we put aggregate return values directly in the sret slot, but this doesn't apply to member pointers which are considered scalar. Unless I'm missing something subtle, we should be able to always use the sret slot directly for indirect return values. Differential revision: https://reviews.llvm.org/D55371 llvm-svn: 348569
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! //===---------------------------------------------------------------------===//