On 11/23/2016 07:57 PM, Bernd Schmidt wrote:
3. ifcvt computes the sum of costs for the involved blocks, but only
makes a before/after comparison when optimizing for size. When
optimizing for speed, it uses max_seq_cost, which is an estimate
computed from BRANCH_COST, which in turn can be zero for predictable
branches on x86.
This is the final patch and has the testcase. It also happens to be the
least risky of the series so it could be applied on its own (without the
test).
Bernd
PR rtl-optimization/78120
* ifcvt.c (noce_conversion_profitable_p): Check original cost in all
cases, and additionally test against max_seq_cost for speed
optimization.
(noce_process_if_block): Compute an estimate for the original cost when
optimizing for speed, using the minimum of then and else block costs.
PR rtl-optimization/78120
* gcc.target/i386/pr78120.c: New test.
Index: gcc/ifcvt.c
===
--- gcc/ifcvt.c (revision 242038)
+++ gcc/ifcvt.c (working copy)
@@ -812,8 +812,10 @@ struct noce_if_info
we're optimizing for size. */
bool speed_p;
- /* The combined cost of COND, JUMP and the costs for THEN_BB and
- ELSE_BB. */
+ /* An estimate of the original costs. When optimizing for size, this is the
+ combined cost of COND, JUMP and the costs for THEN_BB and ELSE_BB.
+ When optimizing for speed, we use the costs of COND plus the minimum of
+ the costs for THEN_BB and ELSE_BB, as computed in the next field. */
unsigned int original_cost;
/* Maximum permissible cost for the unconditional sequence we should
@@ -852,12 +857,12 @@ noce_conversion_profitable_p (rtx_insn *
/* Cost up the new sequence. */
unsigned int cost = seq_cost (seq, speed_p);
+ if (cost <= if_info->original_cost)
+return true;
+
/* When compiling for size, we can make a reasonably accurately guess
- at the size growth. */
- if (!speed_p)
-return cost <= if_info->original_cost;
- else
-return cost <= if_info->max_seq_cost;
+ at the size growth. When compiling for speed, use the maximum. */
+ return speed_p && cost <= if_info->max_seq_cost;
}
/* Helper function for noce_try_store_flag*. */
@@ -3441,15 +3446,24 @@ noce_process_if_block (struct noce_if_in
}
}
- if (! bb_valid_for_noce_process_p (then_bb, cond, _info->original_cost,
+ bool speed_p = optimize_bb_for_speed_p (test_bb);
+ unsigned int then_cost = 0, else_cost = 0;
+ if (!bb_valid_for_noce_process_p (then_bb, cond, _cost,
_info->then_simple))
return false;
if (else_bb
- && ! bb_valid_for_noce_process_p (else_bb, cond, _info->original_cost,
- _info->else_simple))
+ && !bb_valid_for_noce_process_p (else_bb, cond, _cost,
+ _info->else_simple))
return false;
+ if (else_bb == NULL)
+if_info->original_cost += then_cost;
+ else if (speed_p)
+if_info->original_cost += MIN (then_cost, else_cost);
+ else
+if_info->original_cost += then_cost + else_cost;
+
insn_a = last_active_insn (then_bb, FALSE);
set_a = single_set (insn_a);
gcc_assert (set_a);
Index: gcc/testsuite/gcc.target/i386/pr78120.c
===
--- gcc/testsuite/gcc.target/i386/pr78120.c (nonexistent)
+++ gcc/testsuite/gcc.target/i386/pr78120.c (working copy)
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=generic" } */
+/* { dg-final { scan-assembler "adc" } } */
+/* { dg-final { scan-assembler-not "jmp" } } */
+
+typedef unsigned long u64;
+
+typedef struct {
+ u64 hi, lo;
+} u128;
+
+static inline u128 add_u128 (u128 a, u128 b)
+{
+ a.lo += b.lo;
+ if (a.lo < b.lo)
+a.hi++;
+
+ return a;
+}
+
+extern u128 t1, t2, t3;
+
+void foo (void)
+{
+ t1 = add_u128 (t1, t2);
+ t1 = add_u128 (t1, t3);
+}
