[llvm-dev] [RFC] Leaf Attribute Support in Clang/LLVM
Gulfem Savrun Yeniceri via llvm-dev
llvm-dev at lists.llvm.org
Tue Oct 27 17:36:27 PDT 2020
This RFC proposes adding __attribute__((leaf)) support into Clang/LLVM
GCC supports __attribute__((leaf)) as an optimization hint described in:
Fuchsia uses leaf attribute in syscalls, but this attribute is currently
only supported in GCC.
We would like to implement support for this attribute in Clang/LLVM as
This support can benefit Clang/LLVM in two ways:
Achieve feature parity with GCC
Compiler hint to improve data-flow analysis
High Level Design (WIP):
Support __attribute__((leaf)) in Clang
Add a new LLVM IR attribute called nocallback
Modify Clang code generator to generate nocallback attribute for leaf
We choose the name nocallback instead of leaf to avoid confusion. Leaf
attribute does not necessarily mean leaf function in the sense that it does
not call any other functions. As stated in GCC manual, leaf functions are
not allowed to enter their caller's translation unit.
Please let us know about your thoughts regarding this RFC.
I also prepared a patch, so please let us know if you have any feedback.
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