[llvm] r215600 - [AArch64, fast-isel] Fall back to SelectionDAG to select tail calls.

[Chad Rosier]

Seems musttail was landed back in April, but the Phabricator revision was
never closed.  Sounds like a good solution, but again no rush.

> Akira,
> Has the musttail attribute landed?  Looks like Reid was working on
> something (http://reviews.llvm.org/D3240), but I haven't been following
> the patch.  I have no real urgency in seeing this enhancement, so
> prioritize this as you see fit.
>
>  Chad
>
>
>
>> Hi Chad,
>>
>> I’ll see if it’s possible to narrow the scope. We might be able to mark
>> the functions that require special handling as “musttail” instead of
>> “tail” and return false in FastISel::SelectInstruction upon seeing those
>> functions.
>>
>>
>>> On Aug 13, 2014, at 4:55 PM, Chad Rosier <mcrosier at codeaurora.org>
>>> wrote:
>>>
>>> Hi Akira,
>>> Would it be possible to narrow the scope to only those tail calls that
>>> require special handling?  Or is it that the front-end will only emit
>>> tail
>>> calls for those calls that require it at -O0?  Please clarify.
>>>
>>> Chad
>>>
>>>> Author: ahatanak
>>>> Date: Wed Aug 13 18:23:58 2014
>>>> New Revision: 215600
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=215600&view=rev
>>>> Log:
>>>> [AArch64, fast-isel] Fall back to SelectionDAG to select tail calls.
>>>>
>>>> Certain functions such as objc_autoreleaseReturnValue have to be
>>>> called
>>>> as
>>>> tail-calls even at -O0. Since normal fast-isel doesn't emit calls as
>>>> tail
>>>> calls,
>>>> we have to fall back to SelectionDAG to select calls that are marked
>>>> as
>>>> tail.
>>>>
>>>> <rdar://problem/17991614>
>>>>
>>>>
>>>> Added:
>>>>    llvm/trunk/test/CodeGen/AArch64/tailcall-fastisel.ll
>>>> Modified:
>>>>    llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp
>>>>    llvm/trunk/test/CodeGen/AArch64/arm64-abi_align.ll
>>>>
>>>> Modified: llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp?rev=215600&r1=215599&r2=215600&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp (original)
>>>> +++ llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp Wed Aug 13
>>>> 18:23:58
>>>> 2014
>>>> @@ -1687,10 +1687,15 @@ bool AArch64FastISel::FinishCall(CallLow
>>>>
>>>> bool AArch64FastISel::FastLowerCall(CallLoweringInfo &CLI) {
>>>>   CallingConv::ID CC  = CLI.CallConv;
>>>> +  bool IsTailCall     = CLI.IsTailCall;
>>>>   bool IsVarArg       = CLI.IsVarArg;
>>>>   const Value *Callee = CLI.Callee;
>>>>   const char *SymName = CLI.SymName;
>>>>
>>>> +  // Allow SelectionDAG isel to handle tail calls.
>>>> +  if (IsTailCall)
>>>> +    return false;
>>>> +
>>>>   CodeModel::Model CM = TM.getCodeModel();
>>>>   // Only support the small and large code model.
>>>>   if (CM != CodeModel::Small && CM != CodeModel::Large)
>>>>
>>>> Modified: llvm/trunk/test/CodeGen/AArch64/arm64-abi_align.ll
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/arm64-abi_align.ll?rev=215600&r1=215599&r2=215600&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/test/CodeGen/AArch64/arm64-abi_align.ll (original)
>>>> +++ llvm/trunk/test/CodeGen/AArch64/arm64-abi_align.ll Wed Aug 13
>>>> 18:23:58
>>>> 2014
>>>> @@ -511,7 +511,9 @@ entry:
>>>> ; CHECK: str {{w[0-9]+}}, [sp]
>>>> ; FAST-LABEL: i64_split
>>>> ; FAST: ldr x7, [{{x[0-9]+}}]
>>>> -; FAST: str {{w[0-9]+}}, [sp]
>>>> +; FAST: mov x[[R0:[0-9]+]], sp
>>>> +; FAST: orr w[[R1:[0-9]+]], wzr, #0x8
>>>> +; FAST: str w[[R1]], {{\[}}x[[R0]]{{\]}}
>>>>   %0 = load i64* bitcast (%struct.s41* @g41 to i64*), align 16
>>>>   %call = tail call i32 @callee_i64(i32 1, i32 2, i32 3, i32 4, i32 5,
>>>>                                     i32 6, i32 7, i64 %0, i32 8) #5
>>>>
>>>> Added: llvm/trunk/test/CodeGen/AArch64/tailcall-fastisel.ll
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/tailcall-fastisel.ll?rev=215600&view=auto
>>>> ==============================================================================
>>>> --- llvm/trunk/test/CodeGen/AArch64/tailcall-fastisel.ll (added)
>>>> +++ llvm/trunk/test/CodeGen/AArch64/tailcall-fastisel.ll Wed Aug 13
>>>> 18:23:58 2014
>>>> @@ -0,0 +1,11 @@
>>>> +; RUN: llc < %s -mtriple=arm64-apple-darwin -O0 | FileCheck %s
>>>> +
>>>> +; CHECK: b _foo0
>>>> +
>>>> +define i32 @foo1() {
>>>> +entry:
>>>> +  %call = tail call i32 @foo0()
>>>> +  ret i32 %call
>>>> +}
>>>> +
>>>> +declare i32 @foo0()
>>>>
>>>>
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>>>>
>>>
>>>
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>>
>>
>
>
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