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Commit Graph

Author	SHA1	Message	Date
Eric Christopher	afc703da52	Weaken the check for a specific movl on the twoaddr-coalesce-3 test - we only care that there are two moves in the loop and not which part is relative to which register anyhow. llvm-svn: 231191	2015-03-04 01:19:17 +00:00
Eric Christopher	9900a5d037	Update twoaddr-coalesce-3.ll to run on darwin and linux machines: a) Default relocation model differences, b) Different numbers of # in comments llvm-svn: 231178	2015-03-03 23:56:20 +00:00
Eric Christopher	2891913f1a	Fix a problem where the TwoAddressInstructionPass which generate redundant register moves in a loop. From: int M, total; void foo() { int i; for (i = 0; i < M; i++) { total = total + i / 2; } } This is the kernel loop: .LBB0_2: # %for.body =>This Inner Loop Header: Depth=1 movl %edx, %esi movl %ecx, %edx shrl $31, %edx addl %ecx, %edx sarl %edx addl %esi, %edx incl %ecx cmpl %eax, %ecx jl .LBB0_2 -------------------------- The first mov insn "movl %edx, %esi" could be removed if we change "addl %esi, %edx" to "addl %edx, %esi". The IR before TwoAddressInstructionPass is: BB#2: derived from LLVM BB %for.body Predecessors according to CFG: BB#1 BB#2 %vreg3<def> = COPY %vreg12<kill>; GR32:%vreg3,%vreg12 %vreg2<def> = COPY %vreg11<kill>; GR32:%vreg2,%vreg11 %vreg7<def,tied1> = SHR32ri %vreg3<tied0>, 31, %EFLAGS<imp-def,dead>; GR32:%vreg7,%vreg3 %vreg8<def,tied1> = ADD32rr %vreg3<tied0>, %vreg7<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg8,%vreg3,%vreg7 %vreg9<def,tied1> = SAR32r1 %vreg8<kill,tied0>, %EFLAGS<imp-def,dead>; GR32:%vreg9,%vreg8 %vreg4<def,tied1> = ADD32rr %vreg9<kill,tied0>, %vreg2<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg4,%vreg9,%vreg2 %vreg5<def,tied1> = INC64_32r %vreg3<kill,tied0>, %EFLAGS<imp-def,dead>; GR32:%vreg5,%vreg3 CMP32rr %vreg5, %vreg0, %EFLAGS<imp-def>; GR32:%vreg5,%vreg0 %vreg11<def> = COPY %vreg4; GR32:%vreg11,%vreg4 %vreg12<def> = COPY %vreg5<kill>; GR32:%vreg12,%vreg5 JL_4 <BB#2>, %EFLAGS<imp-use,kill> Now TwoAddressInstructionPass will choose vreg9 to be tied with vreg4. However, it doesn't see that there is copy from vreg4 to vreg11 and another copy from vreg11 to vreg2 inside the loop body. To remove those copies, it is necessary to choose vreg2 to be tied with vreg4 instead of vreg9. This code pattern commonly appears when there is reduction operation in a loop. So check for a reversed copy chain and if we encounter one then we can commute the add instruction so we can avoid a copy. Patch by Wei Mi. http://reviews.llvm.org/D7806 llvm-svn: 231148	2015-03-03 22:03:03 +00:00

Author

SHA1

Message

Date

Eric Christopher

afc703da52

Weaken the check for a specific movl on the twoaddr-coalesce-3

test - we only care that there are two moves in the loop and not
which part is relative to which register anyhow.

llvm-svn: 231191

2015-03-04 01:19:17 +00:00

Eric Christopher

9900a5d037

Update twoaddr-coalesce-3.ll to run on darwin and linux machines:

a) Default relocation model differences,
b) Different numbers of # in comments

llvm-svn: 231178

2015-03-03 23:56:20 +00:00

Eric Christopher

2891913f1a

Fix a problem where the TwoAddressInstructionPass which generate redundant register moves in a loop.

From:
int M, total;
void foo() {
int i;
for (i = 0; i < M; i++) {
  total = total + i / 2;
}
}

This is the kernel loop:

.LBB0_2: # %for.body

=>This Inner Loop Header: Depth=1
movl %edx, %esi
movl %ecx, %edx
shrl $31, %edx
addl %ecx, %edx
sarl %edx
addl %esi, %edx
incl %ecx
cmpl %eax, %ecx
jl .LBB0_2
--------------------------
The first mov insn "movl %edx, %esi" could be removed if we change "addl %esi, %edx" to "addl %edx, %esi".

The IR before TwoAddressInstructionPass is:
BB#2: derived from LLVM BB %for.body

Predecessors according to CFG: BB#1 BB#2
    %vreg3<def> = COPY %vreg12<kill>; GR32:%vreg3,%vreg12
    %vreg2<def> = COPY %vreg11<kill>; GR32:%vreg2,%vreg11
    %vreg7<def,tied1> = SHR32ri %vreg3<tied0>, 31, %EFLAGS<imp-def,dead>; GR32:%vreg7,%vreg3
    %vreg8<def,tied1> = ADD32rr %vreg3<tied0>, %vreg7<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg8,%vreg3,%vreg7
    %vreg9<def,tied1> = SAR32r1 %vreg8<kill,tied0>, %EFLAGS<imp-def,dead>; GR32:%vreg9,%vreg8
    %vreg4<def,tied1> = ADD32rr %vreg9<kill,tied0>, %vreg2<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg4,%vreg9,%vreg2
    %vreg5<def,tied1> = INC64_32r %vreg3<kill,tied0>, %EFLAGS<imp-def,dead>; GR32:%vreg5,%vreg3
    CMP32rr %vreg5, %vreg0, %EFLAGS<imp-def>; GR32:%vreg5,%vreg0
    %vreg11<def> = COPY %vreg4; GR32:%vreg11,%vreg4
    %vreg12<def> = COPY %vreg5<kill>; GR32:%vreg12,%vreg5
    JL_4 <BB#2>, %EFLAGS<imp-use,kill>
Now TwoAddressInstructionPass will choose vreg9 to be tied with vreg4. However, it doesn't see that there is copy from vreg4 to vreg11 and another copy from vreg11 to vreg2 inside the loop body. To remove those copies, it is necessary to choose vreg2 to be tied with vreg4 instead of vreg9. This code pattern commonly appears when there is reduction operation in a loop.

So check for a reversed copy chain and if we encounter one then we can commute the add instruction so we can avoid a copy.

Patch by Wei Mi.
http://reviews.llvm.org/D7806

llvm-svn: 231148

2015-03-03 22:03:03 +00:00

3 Commits