https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63949
--- Comment #10 from vekumar at gcc dot gnu.org ---
(In reply to Segher Boessenkool from comment #9)
> A MULT by a constant power of 2 is not canonical RTL (well, not what
> simplify_rtx would give you); combine shouldn't generate this.
In that case we think, we need to fix this heuristic which assumes "MEM"
operation when we encounter a MINUS RTX in "make_compound_operation".
/* Select the code to be used in recursive calls. Once we are inside an
address, we stay there. If we have a comparison, set to COMPARE,
but once inside, go back to our default of SET. */
next_code = (code == MEM ? MEM
: ((code == PLUS || code == MINUS)
&& SCALAR_INT_MODE_P (mode)) ? MEM
: ((code == COMPARE || COMPARISON_P (x))
&& XEXP (x, 1) == const0_rtx) ? COMPARE
: in_code == COMPARE ? SET : in_code);
And later on make_compound_operation converts shift pattern to Mul.
case ASHIFT:
/* Convert shifts by constants into multiplications if inside
an address. */
if (in_code == MEM && CONST_INT_P (XEXP (x, 1))
&& INTVAL (XEXP (x, 1)) < HOST_BITS_PER_WIDE_INT
&& INTVAL (XEXP (x, 1)) >= 0
&& SCALAR_INT_MODE_P (mode))
{
