Hi all,
I now committed this, with changelog
PR rtl-optimization/78232
* combine.c (try_combine): Add a big comment about why reusing i2dest
is undesirable.
(change_zero_ext): Do not call simplify_gen_binary, do the
simplifications manually.
and the patch adds
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -3560,6 +3560,15 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1,
rtx_insn *i0,
{
machine_mode new_mode = GET_MODE (SET_DEST (newpat));
+ /* ??? Reusing i2dest without resetting the reg_stat entry for it
+ (temporarily, until we are committed to this instruction
+ combination) does not work: for example, any call to nonzero_bits
+ on the register (from a splitter in the MD file, for example)
+ will get the old information, which is invalid.
+
+ Since nowadays we can create registers during combine just fine,
+ we should just create a new one here, not reuse i2dest. */
+
/* First try to split using the original register as a
scratch register. */
parallel = gen_rtx_PARALLEL (VOIDmode,
