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[AMDGPU] Use implicit operand to preserve liveness of COPY (llvm#164911)
When lowering spills / restores, we may end up partially lowering the spill via copies and the remaining portion with loads/stores. In this partial lowering case,the implicit-def operands added to the restore load clobber the preceding copies -- telling MachineCopyPropagation to delete them. By also attaching an implicit operand to the load, the COPYs have an artificial use and thus will not be deleted - this is the same strategy taken in llvm#115285 I'm not sure that we need implicit-def operands on any load restore, but I guess it may make sense if it needs to be split into multiple loads and some have been optimized out as containing undef elements. These implicit / implicit-def operands continue to cause correctness issues. A previous / ongoing long term plan to remove them is being addressed via: https://discourse.llvm.org/t/llvm-codegen-rfc-add-mo-lanemask-type-and-a-new-copy-lanemask-instruction/88021 llvm#151123 llvm#151124
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‎llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1874,9 +1874,13 @@ void SIRegisterInfo::buildSpillLoadStore(
18741874
}
18751875

18761876
bool IsSrcDstDef = SrcDstRegState & RegState::Define;
1877+
bool PartialReloadCopy = (RemEltSize != EltSize) && !IsStore;
18771878
if (NeedSuperRegImpOperand &&
1878-
(IsFirstSubReg || (IsLastSubReg && !IsSrcDstDef)))
1879+
(IsFirstSubReg || (IsLastSubReg && !IsSrcDstDef))) {
18791880
MIB.addReg(ValueReg, RegState::Implicit | SrcDstRegState);
1881+
if (PartialReloadCopy)
1882+
MIB.addReg(ValueReg, RegState::Implicit);
1883+
}
18801884

18811885
// The epilog restore of a wwm-scratch register can cause undesired
18821886
// optimization during machine-cp post PrologEpilogInserter if the same

‎llvm/test/CodeGen/AMDGPU/pei-build-spill-partial-agpr.mir‎

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -73,7 +73,7 @@ body: |
7373
; FLATSCR-V2A-NEXT: $agpr0 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr1, implicit $exec, implicit-def $vgpr0_vgpr1, implicit $vgpr0_vgpr1
7474
; FLATSCR-V2A-NEXT: SCRATCH_STORE_DWORD_SADDR killed $vgpr0, $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit killed $vgpr0_vgpr1 :: (store (s32) into %stack.0, addrspace 5)
7575
; FLATSCR-V2A-NEXT: $vgpr1 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit-def $vgpr0_vgpr1
76-
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1 :: (load (s32) from %stack.0, addrspace 5)
76+
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1, implicit $vgpr0_vgpr1 :: (load (s32) from %stack.0, addrspace 5)
7777
; FLATSCR-V2A-NEXT: S_ENDPGM 0
7878
$vgpr0_vgpr1 = IMPLICIT_DEF
7979
SI_SPILL_V64_SAVE killed $vgpr0_vgpr1, %stack.0, $sgpr32, 0, implicit $exec :: (store (s64) into %stack.0, align 4, addrspace 5)
@@ -112,7 +112,7 @@ body: |
112112
; FLATSCR-V2A-NEXT: $agpr0 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr2, implicit $exec, implicit-def $vgpr0_vgpr1_vgpr2, implicit $vgpr0_vgpr1_vgpr2
113113
; FLATSCR-V2A-NEXT: SCRATCH_STORE_DWORDX2_SADDR killed $vgpr0_vgpr1, $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit killed $vgpr0_vgpr1_vgpr2 :: (store (s64) into %stack.0, align 4, addrspace 5)
114114
; FLATSCR-V2A-NEXT: $vgpr2 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit-def $vgpr0_vgpr1_vgpr2
115-
; FLATSCR-V2A-NEXT: $vgpr0_vgpr1 = SCRATCH_LOAD_DWORDX2_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2 :: (load (s64) from %stack.0, align 4, addrspace 5)
115+
; FLATSCR-V2A-NEXT: $vgpr0_vgpr1 = SCRATCH_LOAD_DWORDX2_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2, implicit $vgpr0_vgpr1_vgpr2 :: (load (s64) from %stack.0, align 4, addrspace 5)
116116
; FLATSCR-V2A-NEXT: S_ENDPGM 0
117117
$vgpr0_vgpr1_vgpr2 = IMPLICIT_DEF
118118
SI_SPILL_V96_SAVE killed $vgpr0_vgpr1_vgpr2, %stack.0, $sgpr32, 0, implicit $exec :: (store (s96) into %stack.0, align 4, addrspace 5)
@@ -157,7 +157,7 @@ body: |
157157
; FLATSCR-V2A-NEXT: $vgpr3 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3
158158
; FLATSCR-V2A-NEXT: $vgpr2 = V_ACCVGPR_READ_B32_e64 $agpr1, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3
159159
; FLATSCR-V2A-NEXT: $vgpr1 = V_ACCVGPR_READ_B32_e64 $agpr2, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3
160-
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3 :: (load (s32) from %stack.0, addrspace 5)
160+
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3, implicit $vgpr0_vgpr1_vgpr2_vgpr3 :: (load (s32) from %stack.0, addrspace 5)
161161
; FLATSCR-V2A-NEXT: S_ENDPGM 0
162162
$vgpr0_vgpr1_vgpr2_vgpr3 = IMPLICIT_DEF
163163
SI_SPILL_V128_SAVE killed $vgpr0_vgpr1_vgpr2_vgpr3, %stack.0, $sgpr32, 0, implicit $exec :: (store (s128) into %stack.0, align 4, addrspace 5)
@@ -203,7 +203,7 @@ body: |
203203
; FLATSCR-V2A-NEXT: $agpr0 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr4, implicit $exec, implicit killed $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4
204204
; FLATSCR-V2A-NEXT: $vgpr3 = V_ACCVGPR_READ_B32_e64 $agpr1, implicit $exec, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4
205205
; FLATSCR-V2A-NEXT: $vgpr2 = V_ACCVGPR_READ_B32_e64 $agpr2, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4
206-
; FLATSCR-V2A-NEXT: $vgpr0_vgpr1 = SCRATCH_LOAD_DWORDX2_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4 :: (load (s64) from %stack.0, align 4, addrspace 5)
206+
; FLATSCR-V2A-NEXT: $vgpr0_vgpr1 = SCRATCH_LOAD_DWORDX2_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4 :: (load (s64) from %stack.0, align 4, addrspace 5)
207207
; FLATSCR-V2A-NEXT: $vgpr4 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4
208208
; FLATSCR-V2A-NEXT: S_ENDPGM 0
209209
$vgpr0_vgpr1_vgpr2_vgpr3_vgpr4 = IMPLICIT_DEF
@@ -255,7 +255,7 @@ body: |
255255
; FLATSCR-V2A-NEXT: $vgpr3 = V_ACCVGPR_READ_B32_e64 $agpr2, implicit $exec, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5
256256
; FLATSCR-V2A-NEXT: $vgpr2 = V_ACCVGPR_READ_B32_e64 $agpr3, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5
257257
; FLATSCR-V2A-NEXT: $vgpr1 = V_ACCVGPR_READ_B32_e64 $agpr4, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5
258-
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5 :: (load (s32) from %stack.0, addrspace 5)
258+
; FLATSCR-V2A-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5 :: (load (s32) from %stack.0, addrspace 5)
259259
; FLATSCR-V2A-NEXT: $vgpr5 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5
260260
; FLATSCR-V2A-NEXT: $vgpr4 = V_ACCVGPR_READ_B32_e64 $agpr1, implicit $exec, implicit $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5
261261
; FLATSCR-V2A-NEXT: S_ENDPGM 0

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