On 11/23/2016 07:57 PM, Bernd Schmidt wrote:
2. The i386 backend mishandles SET rtxs. If you have a fairly plain
single-insn SET, you tend to get COSTS_N_INSNS (2) out of set_rtx_cost,
because rtx_costs has a default of COSTS_N_INSNS (1) for a SET, and you
get the cost of the src in addition to that.
Bernd
PR rtl-optimization/78120
* config/i386/i386.c (ix86_rtx_costs): Fully handle SETs.
Index: gcc/config/i386/i386.c
===================================================================
--- gcc/config/i386/i386.c (revision 242038)
+++ gcc/config/i386/i386.c (working copy)
@@ -39925,6 +39925,7 @@ ix86_rtx_costs (rtx x, machine_mode mode
enum rtx_code code = GET_CODE (x);
enum rtx_code outer_code = (enum rtx_code) outer_code_i;
const struct processor_costs *cost = speed ? ix86_cost : &ix86_size_cost;
+ int src_cost;
switch (code)
{
@@ -39935,7 +39936,23 @@ ix86_rtx_costs (rtx x, machine_mode mode
*total = ix86_set_reg_reg_cost (GET_MODE (SET_DEST (x)));
return true;
}
- return false;
+
+ if (register_operand (SET_SRC (x), VOIDmode))
+ /* Avoid potentially incorrect high cost from rtx_costs
+ for non-tieable SUBREGs. */
+ src_cost = 0;
+ else
+ {
+ src_cost = rtx_cost (SET_SRC (x), mode, SET, 1, speed);
+
+ if (CONSTANT_P (SET_SRC (x)))
+ /* Constant costs assume a base value of COSTS_N_INSNS (1) and add
+ a small value, possibly zero for cheap constants. */
+ src_cost += COSTS_N_INSNS (1);
+ }
+
+ *total = src_cost + rtx_cost (SET_DEST (x), mode, SET, 0, speed);
+ return true;
case CONST_INT:
case CONST:
