[LLVMdev] [RFC] Add Intel TSX HLE Support

[Michael Liao]

Here is the patch against clang,
0002-Add-mhle-option-support-and-populate-pre-defined-mac.patch

Yours
- Michael

On Tue, 2013-02-19 at 14:07 -0800, Michael Liao wrote:
> Hi All,
> 
> I'd like to add HLE support in LLVM/clang consistent to GCC's style [1].
> HLE from Intel TSX [2] is legacy compatible instruction set extension to
> specify transactional region by adding XACQUIRE and XRELEASE prefixes.
> To support that, GCC chooses the approach by extending the memory order
> flag in __atomic_* builtins with target-specific memory model in high
> bits (bit 31-16 for target-specific memory model, bit 15-0 for the
> general memory model.) To follow the similar approach, I propose to
> change LLVM/clang by adding:
> 
> + a metadata 'targetflags' in LLVM atomic IR to pass this
>   target-specific memory model hint
> 
> + one extra target flag in AtomicSDNode & MemIntrinsicSDNode to specify
> XACQUIRE or XRELEASE hints
>   This extra target flag is embedded into the SubclassData fields. The
> following is rationale how such target flags are embedded into
> SubclassData in SDNode
> 
>   here is the current SDNode class hierarchy of memory related nodes
> 
>   SDNode -> MemSDNode -> LSBaseNode -> LoadSDNode
>                     |             + -> StoreSDNode
>                     + -> AtomicSDNode
>                     + -> MemIntrinsicSDNode
> 
>   here is the current SubclassData definitions:
> 
>   bit 0~1 : extension type used in LoadSDNode
>   bit 0   : truncating store in StoreSDNode
>   bit 2~4 : addressing mode in LSBaseNode
>   bit 5   : volatile bit in MemSDNode
>   bit 6   : non-temporal bit in MemSDNode
>   bit 7   : invariant bit in MemSDNode
>   bit 8~11: memory order in AtomicSDNode
>   bit 12  : synch scope in AtomicSDNode
> 
>   Considering the class hierarchy, we could safely reused bit 0~1 as the
> target flags in AtomicSDNode/MemIntrinsicNode
>   
> + X86 backend is modified to generate additional XACQUIRE/XRELEASE
> prefix based on the specified target flag
> 
> 
> The following are details of each patch:
> 
> * 0001-Add-targetflags-in-AtomicSDNode-MemIntrinsicSDNode.patch
> 
> This patch adds 'targetflags' support in AtomicSDNode and
> MemIntrinsicSDNode. It will check metadata 'targetflags' and embedded
> its value into SubclassData. Currently, only two bits are defined.
> 
> * 0002-Add-HLE-target-feature.patch
> 
> This patch adds HLE feature and auto-detection support
> 
> * 0003-Add-XACQ-XREL-prefix-and-encoding-asm-printer-suppor.patch
> 
> This patch adds XACQUIRE/XRELEASE prefix and its assembler/encoding
> support
> 
> * 0004-Enable-HLE-code-generation.patch
> 
> This patch enables HLE code generation by extending the current logic to
> handle 'targetflags'.
> 
> * 0001-Add-target-flags-support-for-atomic-ops.patch
> 
> This patch adds target flags support in __atomic_* builtins. It splits
> the whole 32-bit order word into high and low 16-bit parts. The low
> 16-bit is the original memory order and the high 16-bit will be
> re-defined as target-specific flags and passed through 'targetflags'
> metadata.
> 
> * 0002-Add-mhle-option-support-and-populate-pre-defined-mac.patch
> 
> It adds '-m[no]hle' option to turn on HLE feature or not. Once HLE
> feature is turned on, two more macros (__ATOMIC_HLE_ACQUIRE and
> __ATOMIC_HLE_RELEASE) are defined for developers to mark atomic
> builtins.
> 
> Thanks for your time to review!
> 
> Yours
> - Michael
> ---
> [1] http://gcc.gnu.org/ml/gcc-patches/2012-04/msg01073.html
> [2] http://software.intel.com/sites/default/files/319433-014.pdf
> 

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