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Add more info to FIXME.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134729 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jim Grosbach 2011-07-08 20:18:11 +00:00
parent e36e21e830
commit 8dc41f33f7
1 changed files with 5 additions and 1 deletions
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6
lib/Target/ARM/ARMISelLowering.cpp
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@ -1637,7 +1637,11 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
return false;
// FIXME: Completely disable sibcall for Thumb1 since Thumb1RegisterInfo::
// emitEpilogue is not ready for them.
// emitEpilogue is not ready for them. Thumb tail calls also use t2B, as
// the Thumb1 16-bit unconditional branch doesn't have sufficient relocation
// support in the assembler and linker to be used. This would need to be
// fixed to fully support tail calls in Thumb1.
//
// Doing this is tricky, since the LDM/POP instruction on Thumb doesn't take
// LR. This means if we need to reload LR, it takes an extra instructions,
// which outweighs the value of the tail call; but here we don't know yet