craig.topper added inline comments.
================ Comment at: llvm/test/CodeGen/X86/zero-call-used-regs-fmod.ll:15 +; CHECK-NEXT: xorps %xmm1, %xmm1 +; CHECK-NEXT: popq %rax +; CHECK-NEXT: .cfi_def_cfa_offset 8 ---------------- void wrote: > craig.topper wrote: > > Is it ok that this popq popped garbage into the %rax after you cleared it? > > It's not the return value of the function. That's xmm0. This is just a popq > > because its a shorter encoding than `sub 8, %esp` > It's getting the value back from the `pushq %rax` instruction, isn't it? We > shouldn't be clearing it, though. I'll see if I can fix that. There was a mistake in my previous comment. The popq is being used in place of `add 8, %rsp` In this case it probably is the value from the pushq. But %rax isn't a function argument so it is effectively garbage data. This is X86FrameLowering::emitSPUpdate scavenging %rax to use a pushq/popq instead of subtracting or adding to %rsp. I think this is being done to align the stack for the call to fmod, but I'm not sure. I think we can use a pushq like this to allocate stack space that gets overwritten before the popq. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D110869/new/ https://reviews.llvm.org/D110869 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
