https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71768
Jan Hubicka <hubicka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2016-07-05
CC| |vmakarov at redhat dot com
Ever confirmed|0 |1
--- Comment #1 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I looked into this a bit as it seemed to be easy to fix, but i don't see how
exactly rematerialization triggers here.
The following testcase:
const float cst=1;
int t()
{
float val = cst;
asm("#%0"::"x"(val));
e();
asm("#%0"::"x"(val));
}
looks almost identical pre-ira and is optimized as expected. The difference in
reloading seems to start here:
@@ -78,17 +78,14 @@
Hard reg set forest:
0:( 0-6 8-15 21-52)@0
1:( 0-6 37-44)@12000
- 2:( 21-28 45-52)@16000
+ Spill a1(r88,l0)
The reason here is that allocno's class_cost is not greater than memory_cost in
the vector case. I guess either class_cost or memory_cost is not computed
correctly which seems to be done by record_reg_classes that does quite some
guesswork.
Later LRA misses the equivalence in the second case:
@@ -10,12 +10,55 @@
Can eliminate 16 to 6 (offset=8, prev_offset=0)
Can eliminate 20 to 7 (offset=0, prev_offset=0)
Can eliminate 20 to 6 (offset=-8, prev_offset=0)
- alt=0: Bad operand -- refuse
- alt=1: Bad operand -- refuse
- alt=2,overall=0,losers=0,rld_nregs=0
- Choosing alt 2 in insn 5: (0) v (1) vm {movv4si_internal}
- alt=0,overall=0,losers=0,rld_nregs=0
+ Removing equiv init insn 5 (freq=1000)
+ 5: r88:SF=[`*.LC0']
+ REG_EQUIV 1.0e+0
+deleting insn with uid = 5.
+Changing pseudo 88 in operand 0 of insn 6 on equiv 1.0e+0
+ 0 Non-pseudo reload: reject+=2
+ 0 Non input pseudo reload: reject++
+ alt=0,overall=15,losers=2,rld_nregs=1
Choosing alt 0 in insn 6: (0) x
+ Creating newreg=90, assigning class SSE_REGS to r90
+ 6: {asm_operands;clobber fpsr:CCFP;clobber flags:CC;}
+ REG_UNUSED fpsr:CCFP
+ REG_UNUSED flags:CC
+ Inserting insn reload before:
+ 18: r90:SF=[`*.LC0']
I wonder why LRA behaves this way. Even if the register is not spilled, it can
be rematerialized.
