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

[Akira Hatanaka]

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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