[all-commits] [llvm/llvm-project] 18ccca: [UBSan] Consider zero input to __builtin_clz/ctz t...

Craig Topper via All-commits all-commits at lists.llvm.org
Fri Jun 2 13:01:31 PDT 2023

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 18ccca4da8dec5fbfd1072a1c1544ce25f528627
  Author: Craig Topper <craig.topper at sifive.com>
  Date:   2023-06-02 (Fri, 02 Jun 2023)

  Changed paths:
    M clang/lib/CodeGen/CGBuiltin.cpp
    M clang/test/CodeGen/ubsan-builtin-checks.c

  Log Message:
  [UBSan] Consider zero input to __builtin_clz/ctz to be undefined independent of the target.

Previously we checked isCLZForZeroUndef and only added UBSan checks
if it returned true.

The builtin should be considered undefined for 0 regardless of
the target so that code using it is portable. The isCLZForZeroUndef
was only intended to disable optimizations in the middle end and

See https://discourse.llvm.org/t/should-ubsan-detect-0-input-to-builtin-clz-ctz-regardless-of-target/71060

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D152023

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