[PATCH] D24818: Using branch probability to guide critical edge splitting.

[David Li via llvm-commits]

davidxl added a comment.

A related comment -- (no need to be addressed here):

If a instruction defines value that is used via more than one cold edges (split or to be split), the MachineSink should probably be enhanced to let it sunk. For instance in the attached the CFG,  mov $0x8000000, %r12d should be sunk into La0, Lb0 and Lb7 from L40.

digraph  foo  {
node [shape=box]
size="11,8.5"
_exit_ [label="_exit_\n ", style=filled, color=gray]
L0000000000000000 [label="L0000000000000000\n<foo>: \n ", style=filled, color=gray]
L0 [label="L0\npush %rbp \n ", style=filled, color=gray]
https://reviews.llvm.org/L1 [label="https://reviews.llvm.org/L1\npush %r15 \npush %r14 \n ", style=filled, color=gray]
L5 [label="L5\npush %r13 \n ", style=filled, color=gray]
L7 [label="L7\npush %r12 \npush %rbx \n ", style=filled, color=gray]
La [label="La\nsub $0x18,%rsp \n ", style=filled, color=gray]
Le [label="Le\nmov %rcx,%r14 \nmov %esi,%ebp \ntest %ebp,%ebp \njle e7 <foo+0xe7>\n ", style=filled, color=gray]
L1b [label="L1b\n.. \n ", style=filled, color=gray]
L40 [label="L40\n..\nmov $0x80000000,%r12d \ntest %eax,%eax \njs a0 <foo+0xa0>\n ", style=filled, color=gray]
L52 [label="L52\n..\njs b0 <foo+0xb0>\n ", style=filled, color=gray]
L5f [label="L5f\n..\njs b7 <foo+0xb7>\n ", style=filled, color=gray]
L71 [label="L71\n..\nmov %eax,%r12d \nand $0x80000000,%r12d \n..jmp c0 <foo+0xc0>\n", style=filled, color=gray]
La0 [label="La0\nxor %ebx,%ebx \njmp c0 <foo+0xc0>\ndata32 data32 nopw\n ", style=filled, color=gray]
Lb0 [label="Lb0\nmov $0x1,%ebx \njmp c0 <foo+0xc0>\n ", style=filled, color=gray]
Lb7 [label="Lb7\nmov $0x2,%ebx \nnopl 0x0(%rax) \n ", style=filled, color=gray]
Lc0 [label="Lc0\nmov %ebx,%edi \nmov %r12d,%esi \ncallq ca <foo+0xca>\nxor %eax,%eax \n.. \njs df <foo+0xdf>\n ", style=filled, color=gray]
Ld5 [label="Ld5\nmov %ebx,%edi \nmov %r12d,%esi \ncallq df <foo+0xdf>\n ", style=filled, color=gray]
Ldf [label="Ldf\ndec %ebp \njne 40 <foo+0x40>\n ", style=filled, color=gray]
Le7 [label="Le7\nadd $0x18,%rsp \npop %rbx \npop %r12 \npop %r13 \npop %r14 \npop %r15 \npop %rbp \nretq \n ", style=filled, color=gray]
L0000000000000000 -> L0 ;
L0 -> https://reviews.llvm.org/L1 ;
https://reviews.llvm.org/L1 -> L5 ;
L5 -> L7 ;
L7 -> La ;
La -> Le ;
Le -> Le7 ;
Le -> L1b ;
L1b -> L40 ;
L40 -> La0 ;
L40 -> L52 ;
L52 -> Lb0 ;
L52 -> L5f ;
L5f -> Lb7 ;
L5f -> L71 ;
L71 -> Lc0 ;
La0 -> Lc0 ;
Lb0 -> Lc0 ;
Lb7 -> Lc0 ;
Lc0 -> Ldf ;
Lc0 -> Ld5 ;
Ld5 -> Ldf ;
Ldf -> L40 ;
Ldf -> Le7 ;
Le7 -> _exit_ ;
}


https://reviews.llvm.org/D24818