Miscompile with [[clang::musttail]]

[gerben-stavenga]

When adding [[clang::musttail]] to a tail function call the program crashes. Inspection of the output asm clearly shows the stack return address is written over by a skewed memcpy, it copies the struct that is passed on the stack over itself but with a shift of 16 globbering the return address. Without [[clang::musttail] the function runs correctly and -fsanitize=undefined,asan does not indicate any problems

https://godbolt.org/z/Y7fq1xK54

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: None (gerben-stavenga)

When adding [[clang::musttail]] to a tail function call the program crashes. Inspection of the output asm clearly shows the stack return address is written over by a skewed memcpy, it copies the struct that is passed on the stack over itself but with a shift of 16 globbering the return address. Without [[clang::musttail] the function runs correctly and -fsanitize=undefined,asan does not indicate any problems

https://godbolt.org/z/Y7fq1xK54

[gerben-stavenga]

A simpler repro
https://godbolt.org/z/Ys5G6xnaz

at line 5 you see a copy over [rsp] which of course contains the return address