https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69564
--- Comment #21 from Patrick Palka <ppalka at gcc dot gnu.org> ---
To be clear, given the loop
for (int i = 0; i < M; i++) { ... }
The fold_build3 in question was transforming
if (i < M)
fallthrough;
else
goto exit;
to
if (i >= M)
goto exit;
else
fallthrough;
The C FE emits
if (i < M)
goto body;
else
goto L;
L:
I would guess r217669 introduced the regression. Before this commit the two
arms of the COND_EXPR would be GOTO_EXPRs and so during folding
tree_swap_operands_p would return false. After this commit, the true arm is an
empty statement which is TREE_CONSTANT and so during folding
tree_swap_operands_p returns true.
The tree dumps do not seem to diverge significantly with and without the above
patch. The only difference throughout is the inversion of the branches.
