https://bugs.llvm.org/show_bug.cgi?id=47538
Bug ID: 47538
Summary: implement -mskip-rax-setup
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: ndesaulni...@google.com
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, spatel+l...@rotateright.com
Blocks: 4068
Via
https://patchwork.ozlabs.org/project/gcc/patch/20141218131150.ga32...@intel.com/
The Linux kernel never passes floating point arguments around, vararg
functions or not. Hence no vector registers are ever used when calling a
vararg function. But gcc still dutifully emits an "xor %eax,%eax" before
each and every call of a vararg function. Since no callee use that for
anything, these instructions are redundant.
This patch adds the -mskip-rax-setup option to skip setting up RAX
register when SSE is disabled and there are no variable arguments passed
in vector registers.
Referenced Bugs:
https://bugs.llvm.org/show_bug.cgi?id=4068
[Bug 4068] [Meta] Compiling the Linux kernel with clang
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