Add @naked UDA #2773
Add @naked UDA #2773
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Motivation: being able to replace the DMD-style naked asm functions with LLVM asm + @naked UDA, in order to get LTO working with druntime/Phobos on Windows. |
gen/uda.cpp
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| namespace llvm { | ||
| // Auto-generate: | ||
| // Attribute::AttrKind getAttrKindFromName(StringRef AttrName) { ... } |
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Yeah, took me a bit of time. ;) - Let's see which LLVM versions support this.
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LGTM. Would be nice to add a link to the LLVM langref |
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There's no direct URL to the |
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As preparation for a trivial addition to ldc.attributes, probably more
to follow over time:
enum naked = llvmAttr("naked");
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I didn't find a similar function in LLVM 3.7 and 3.8, so this kind of |
| @@ -13,6 +13,20 @@ | |||
| #include "id.h" | |||
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| #include "llvm/ADT/StringExtras.h" | |||
| #include "llvm/ADT/StringSwitch.h" | |||
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This include looks unnecessary.
I more meant that'd it be nice to say explicitly that the UDA is applying the LLVM |
gen/uda.cpp
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| #else | ||
| // no getAttrKindFromName(); just detect `naked` for now | ||
| if (key == "naked") { | ||
| func->addFnAttr(llvm::Attribute::Naked) |
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forgot return here. Better to use an if-else chain to prevent such errors?
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Wow, even managed to forget the semicolon. ;)
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It may need to do more than just applying the LLVM attribute. We shouldn't allocate storage for implicit and explicit parameters (our 'prologue'); I had to resort to defining a parameter-less impl-function and overriding its mangle in order to fake a naked function taking 2 params. |
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LDC prologue/epilogue now disabled too, which seems to work fine for Win64. On Linux x64 however, the 2 params of the testcase are still dumped to memory; the generated IR is exactly the same as the Win64 one, incl. function attributes: ; Function Attrs: naked uwtable
define i32 @nakedFunction(i32 %param1_arg, i8* %param2_arg) #0 comdat {
%1 = call i32 asm sideeffect "xor %eax, %eax", "={eax}"() ; [#uses = 1]
ret i32 %1
}The faulty Linux .s, params dumped inbetween inline asm and return instruction: nakedFunction:
.cfi_startproc
#APP
xorl %eax, %eax
#NO_APP
movl %edi, -4(%rbp)
movq %rsi, -16(%rbp)
retq |
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Alright, same thing for Linux happening with clang. The updated version doesn't require a return statement anymore (and so allows for naked functions without return instruction or with manual ones only), see the extended test. The appended unreachable vanishes for Linux (not in unoptimized |
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