On Fri, 30 Oct 2015, Richard Biener wrote:
+/* Convert (A + A) * C -> A * 2 * C. */ +(simplify + (mult:c (convert? (plus @0 @0)) (convert? @1)) + (if (tree_nop_conversion_p (TREE_TYPE (@0), type)) + (convert (mult @0 (mult { build_int_cst (TREE_TYPE (@1), 2); } @1))))) +(simplify + (mult:c (convert? (plus @0 @0)) INTEGER_CST@1) + (if (tree_nop_conversion_p (TREE_TYPE (@0), type)) + (convert (mult @0 (mult { build_int_cst (TREE_TYPE (@1), 2); } @1)))))fold-const.c only handles constant C, so we only need to 2nd pattern. Also the :c on the mult in that is not needed due to canonicalization rules. Please build the result of the inner multiplication directly. I think the fold-const.c code has an overflow issue when the outer multiplication is signed and the inner addition unsigned. (signed)((unsigned)INT_MAX + (unsigned)INT_MAX)*2 is valid but INT_MAX * 4 is not as it overflows. So I think we should _not_ allow nop conversions here (it's fine if all ops are signed or unsigned).
Is there a reason why the simple transformation A+A->2*A is not generally a desirable canonicalization? We currently restrict it to SCALAR_FLOAT_TYPE_P. -- Marc Glisse
