Dear All, I am new to Haskell so please forgive me if I am asking about something already well-understood. I was trying to understand the performance of my Haskell program compiled with the LLVM backend. I used -ddump-llvm to dump the LLVM assembly and then ran llc -O3 on the resulting file to look at the native assembly. One of the generated function starts off with s5BH_info: # @s5BH_info # BB#0: subq $208, %rsp movq %r13, 200(%rsp) movq %rbp, 192(%rsp) movq %r12, 184(%rsp) movq %rbx, 176(%rsp) movq %r14, 168(%rsp) movq %rsi, 160(%rsp) movq %rdi, 152(%rsp) movq %r8, 144(%rsp) movq %r9, 136(%rsp) movq %r15, 128(%rsp) movss %xmm1, 124(%rsp) movss %xmm2, 120(%rsp) movss %xmm3, 116(%rsp) movss %xmm4, 112(%rsp) movsd %xmm5, 104(%rsp) movsd %xmm6, 96(%rsp) At some point down the line the function makes a tail call to itself and this is the code generated movq %r14, 168(%rsp) movq 200(%rsp), %r13 movq 192(%rsp), %rbp movq 184(%rsp), %r12 movq 176(%rsp), %rbx movq 128(%rsp), %r15 movsd 104(%rsp), %xmm5 addq $208, %rsp jmp s5BH_info So it looks like some values are being moved from registers to the stack only to be immediately moved from the stack to the register on entry to the function. It should be possible to eliminate both the load and the stores. Is this behaviour due to LLVM or GHC? If it is GHC, it this an optimization a newcomer can attempt to implement or are there deep issues here? Jyotirmoy Bhattacharya