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clang-p2996/llvm/test/CodeGen/AMDGPU/fix-wwm-liveness.mir
Tim Renouf abd85fb1f5 [AMDGPU] Reworked SIFixWWMLiveness 
Summary:
I encountered some problems with SIFixWWMLiveness when WWM is in a loop:

1. It sometimes gave invalid MIR where there is some control flow path
   to the new implicit use of a register on EXIT_WWM that does not pass
   through any def.

2. There were lots of false positives of registers that needed to have
   an implicit use added to EXIT_WWM.

3. Adding an implicit use to EXIT_WWM (and adding an implicit def just
   before the WWM code, which I tried in order to fix (1)) caused lots
   of the values to be spilled and reloaded unnecessarily.

This commit is a rework of SIFixWWMLiveness, with the following changes:

1. Instead of considering any register with a def that can reach the WWM
   code and a def that can be reached from the WWM code, it now
   considers three specific cases that need to be handled.

2. A register that needs liveness over WWM to be synthesized now has it
   done by adding itself as an implicit use to defs other than the
   dominant one.

Also added the following fixmes:

FIXME: We should detect whether a register in one of the above
categories is already live at the WWM code before deciding to add the
implicit uses to synthesize its liveness.

FIXME: I believe this whole scheme may be flawed due to the possibility
of the register allocator doing live interval splitting.

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D46756

Change-Id: Ie7fba0ede0378849181df3f1a9a7a39ed1a94a94
llvm-svn: 338783
2018-08-02 23:31:32 +00:00

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# RUN: llc -march=amdgcn -verify-machineinstrs -run-pass si-fix-wwm-liveness -o - %s | FileCheck %s
# Test a then phi value.
#CHECK: test_wwm_liveness_then_phi
#CHECK: %21:vgpr_32 = V_MOV_B32_e32 1, implicit $exec, implicit %21
---
name: test_wwm_liveness_then_phi
alignment: 0
exposesReturnsTwice: false
legalized: false
regBankSelected: false
selected: false
tracksRegLiveness: true
registers:
- { id: 0, class: sreg_64, preferred-register: '' }
- { id: 1, class: sgpr_32, preferred-register: '' }
- { id: 2, class: sgpr_32, preferred-register: '' }
- { id: 3, class: vgpr_32, preferred-register: '' }
- { id: 4, class: vgpr_32, preferred-register: '' }
- { id: 5, class: vgpr_32, preferred-register: '' }
- { id: 6, class: vgpr_32, preferred-register: '' }
- { id: 7, class: vgpr_32, preferred-register: '' }
- { id: 8, class: sreg_64, preferred-register: '$vcc' }
- { id: 9, class: sreg_64, preferred-register: '' }
- { id: 10, class: sreg_32_xm0, preferred-register: '' }
- { id: 11, class: sreg_64, preferred-register: '' }
- { id: 12, class: sreg_32_xm0, preferred-register: '' }
- { id: 13, class: sreg_32_xm0, preferred-register: '' }
- { id: 14, class: sreg_32_xm0, preferred-register: '' }
- { id: 15, class: sreg_128, preferred-register: '' }
- { id: 16, class: vgpr_32, preferred-register: '' }
- { id: 17, class: vgpr_32, preferred-register: '' }
- { id: 18, class: vgpr_32, preferred-register: '' }
- { id: 19, class: sreg_64, preferred-register: '' }
- { id: 20, class: sreg_64, preferred-register: '' }
- { id: 21, class: vgpr_32, preferred-register: '' }
- { id: 22, class: sreg_64, preferred-register: '' }
- { id: 23, class: sreg_64, preferred-register: '' }
liveins:
body: |
bb.0:
successors: %bb.1(0x40000000), %bb.2(0x40000000)
%21 = V_MOV_B32_e32 0, implicit $exec
%5 = V_MBCNT_LO_U32_B32_e64 -1, 0, implicit $exec
%6 = V_MBCNT_HI_U32_B32_e32 -1, killed %5, implicit $exec
%8 = V_CMP_GT_U32_e64 32, killed %6, implicit $exec
%22 = COPY $exec, implicit-def $exec
%23 = S_AND_B64 %22, %8, implicit-def dead $scc
%0 = S_XOR_B64 %23, %22, implicit-def dead $scc
$exec = S_MOV_B64_term killed %23
SI_MASK_BRANCH %bb.2, implicit $exec
S_BRANCH %bb.1
bb.1:
successors: %bb.2(0x80000000)
%13 = S_MOV_B32 61440
%14 = S_MOV_B32 -1
%15 = REG_SEQUENCE undef %12, 1, undef %10, 2, killed %14, 3, killed %13, 4
%19 = COPY $exec
$exec = S_MOV_B64 -1
%16 = BUFFER_LOAD_DWORD_OFFSET %15, 0, 0, 0, 0, 0, implicit $exec :: (volatile load 4)
%17 = V_ADD_F32_e32 1065353216, killed %16, implicit $exec
$exec = EXIT_WWM killed %19
%21 = V_MOV_B32_e32 1, implicit $exec
early-clobber %18 = WWM killed %17, implicit $exec
BUFFER_STORE_DWORD_OFFSET killed %18, killed %15, 0, 0, 0, 0, 0, implicit $exec :: (store 4)
bb.2:
$exec = S_OR_B64 $exec, killed %0, implicit-def $scc
$vgpr0 = COPY killed %21
SI_RETURN_TO_EPILOG killed $vgpr0
...
# Test a loop with a loop exit value and a loop phi.
#CHECK: test_wwm_liveness_loop
#CHECK: %4:vgpr_32 = IMPLICIT_DEF
#CHECK: bb.1:
#CHECK: %4:vgpr_32 = FLAT_LOAD_DWORD{{.*}}, implicit %4
#CHECK: %27:vgpr_32 = COPY killed %21, implicit %27
---
name: test_wwm_liveness_loop
alignment: 0
exposesReturnsTwice: false
legalized: false
regBankSelected: false
selected: false
failedISel: false
tracksRegLiveness: true
registers:
- { id: 0, class: vgpr_32, preferred-register: '' }
- { id: 1, class: sreg_32_xm0, preferred-register: '' }
- { id: 2, class: sreg_64, preferred-register: '' }
- { id: 3, class: sreg_32_xm0, preferred-register: '' }
- { id: 4, class: vgpr_32, preferred-register: '' }
- { id: 5, class: sreg_32_xm0, preferred-register: '' }
- { id: 6, class: sreg_64, preferred-register: '' }
- { id: 7, class: sreg_64, preferred-register: '' }
- { id: 8, class: sreg_64, preferred-register: '' }
- { id: 9, class: vreg_64, preferred-register: '' }
- { id: 10, class: vgpr_32, preferred-register: '' }
- { id: 11, class: vgpr_32, preferred-register: '' }
- { id: 12, class: vgpr_32, preferred-register: '' }
- { id: 13, class: sreg_64, preferred-register: '' }
- { id: 14, class: vreg_64, preferred-register: '' }
- { id: 15, class: sreg_32_xm0, preferred-register: '' }
- { id: 16, class: vgpr_32, preferred-register: '' }
- { id: 17, class: sreg_64, preferred-register: '$vcc' }
- { id: 18, class: vgpr_32, preferred-register: '' }
- { id: 19, class: vgpr_32, preferred-register: '' }
- { id: 20, class: vgpr_32, preferred-register: '' }
- { id: 21, class: vgpr_32, preferred-register: '' }
- { id: 22, class: vgpr_32, preferred-register: '' }
- { id: 23, class: sreg_64, preferred-register: '' }
- { id: 24, class: sreg_64, preferred-register: '' }
- { id: 25, class: sreg_64, preferred-register: '' }
- { id: 26, class: sreg_64, preferred-register: '' }
- { id: 27, class: vgpr_32, preferred-register: '' }
liveins:
frameInfo:
isFrameAddressTaken: false
isReturnAddressTaken: false
hasStackMap: false
hasPatchPoint: false
stackSize: 0
offsetAdjustment: 0
maxAlignment: 0
adjustsStack: false
hasCalls: false
stackProtector: ''
maxCallFrameSize: 4294967295
hasOpaqueSPAdjustment: false
hasVAStart: false
hasMustTailInVarArgFunc: false
localFrameSize: 0
savePoint: ''
restorePoint: ''
fixedStack:
stack:
constants:
body: |
bb.0:
successors: %bb.1(0x80000000)
%25:sreg_64 = S_OR_SAVEEXEC_B64 -1, implicit-def $exec, implicit-def dead $scc, implicit $exec
%0:vgpr_32 = FLAT_LOAD_DWORD undef %9:vreg_64, 0, 0, 0, implicit $exec, implicit $flat_scr :: (volatile load 4 from `float addrspace(1)* undef`, addrspace 1)
$exec = EXIT_WWM killed %25
%12:vgpr_32 = V_MBCNT_LO_U32_B32_e64 -1, 0, implicit $exec
%7:sreg_64 = S_MOV_B64 0
%26:sreg_64 = COPY killed %7
%27:vgpr_32 = COPY killed %12
bb.1:
successors: %bb.2(0x04000000), %bb.1(0x7c000000)
%24:sreg_64 = S_OR_SAVEEXEC_B64 -1, implicit-def $exec, implicit-def dead $scc, implicit $exec
%20:vgpr_32 = COPY killed %27
%2:sreg_64 = COPY killed %26
%4:vgpr_32 = FLAT_LOAD_DWORD undef %14:vreg_64, 0, 0, 0, implicit $exec, implicit $flat_scr :: (volatile load 4 from `float addrspace(1)* undef`, addrspace 1)
$exec = EXIT_WWM killed %24
%22:vgpr_32 = V_ADD_I32_e32 -1, killed %20, implicit-def dead $vcc, implicit $exec
%17:sreg_64 = V_CMP_EQ_U32_e64 0, %22, implicit $exec
%6:sreg_64 = S_OR_B64 killed %17, killed %2, implicit-def $scc
%21:vgpr_32 = COPY killed %22
%26:sreg_64 = COPY %6
%27:vgpr_32 = COPY killed %21
$exec = S_ANDN2_B64_term $exec, %6
S_CBRANCH_EXECNZ %bb.1, implicit $exec
S_BRANCH %bb.2
bb.2:
$exec = S_OR_B64 $exec, killed %6, implicit-def $scc
%23:sreg_64 = S_OR_SAVEEXEC_B64 -1, implicit-def $exec, implicit-def dead $scc, implicit $exec
%18:vgpr_32 = V_ADD_F32_e32 killed %0, killed %4, implicit $exec
$exec = EXIT_WWM killed %23
early-clobber %19:vgpr_32 = COPY killed %18, implicit $exec
$vgpr0 = COPY killed %19
SI_RETURN_TO_EPILOG killed $vgpr0
...
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