[PATCH] D136532: [clang][Interp] Implement left and right shifts

[Shafik Yaghmour via Phabricator via cfe-commits]

shafik added inline comments.


================
Comment at: clang/test/AST/Interp/shifts.cpp:70
+    i = 1 << (WORD_BIT - 1); // cxx17-warning-not {{sets the sign bit of the shift expression}}
+    i = -1 << (WORD_BIT - 1); // cxx17-warning {{shifting a negative signed value is undefined}} \
+                              // ref-cxx17-warning {{shifting a negative signed value is undefined}}
----------------
shafik wrote:
> A negative left operand was made well-formed in C++20 I believe see godbolt: https://godbolt.org/z/7qzKjojMb
> 
> My reference from above for `expr.shift/p1` also applies. 
> 
> Although a negative right operand is still UB.
> 
> Also note shifting into the sign bit was made well-formed in C++11: https://stackoverflow.com/questions/19593938/is-left-shifting-a-negative-integer-undefined-behavior-in-c11#comment29091986_19593938
Typo, shifting into the sign bit was made well-formed after C++11


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136532/new/

https://reviews.llvm.org/D136532