The strength reduction (SR) phase mishandled the END pseudo when SR
found at least 2 different expressions in the same loop, and SR made a
new header for the loop.
Since 1987 (commit 159b84e), SR appended the new header to the end of
the procedure. Later, SR fixed the header by adding a BRA branch to
the loop's entry, and moving the END pseudo from the previous basic
block to the header. If SR found multiple expressions, it called
fix_header() multiple times, and tried to move the END again. The
extra move failed assert(INSTR(e) == ps_end), or moved another line
after the END, so opt2 (the peephole optimizer) would crash.
Fix by removing fix_header() and moving the code to make_header(), so
SR adds the BRA and moves the END when it makes the header, and does
so only once for each header.
Adjust init_code(), which inserts code into a header. Stop checking
for an empty header, because make_header() now adds BRA. After
inserting code before BRA, don't move LP_INSTR, because later
insertions should go before BRA, not after END.
e841adf970