[AMDGPU] Fixed v_swap_b32 match

[rampitec]

Summary

1. Fixed liveness issue with implicit kills.
2. Fixed potential problem with an indirect mov.

Fixes: SWDEV-256848

[arsenm]

Couldn't this try to preserve the implicit operands?

[rampitec]

In D89599#2336763, @arsenm wrote:

Couldn't this try to preserve the implicit operands?

It can be implicit def or implicit kill. In both cases verifier will complain if it is dropped. Then the problem is there can be other instructions in between of the combined three and correct licenses may be needed in that range. That is probably possible to preserve implicit operands on the move at the insertion point and carry it over to the swap, but I am not so sure about the other two. Insert there an IMPLICIT_DEF or KILL?

[rampitec]

Preserve implicit operands on the mov at insertion point.

[rampitec]

Preserve implicit operands.

[arsenm]

llvm/lib/Target/AMDGPU/SIShrinkInstructions.cpp

442–447

Rather than special casing exec, this should check if the number of operands matches the number in the MCInstrDesc

[rampitec]

Do not specaial case implicit exec.

[Paul-C-Anagnostopoulos]

When I build the latest version of the AMDGPU target, I get the warning shown below, which was treated as an error. I believe it started happening with this revision. I'm running on Windows.

Does it need to be:

if (Size > 1 && (I->getNumImplicitOperands() > (I->isCopy() ? 0U : 1U)))

---

...SIShrinkInstructions.cpp(551): warning C4018: '>': signed/unsigned mismatch

[Paul-C-Anagnostopoulos]

Yes, making the 0 and 1 unsigned fixes the problem.

[rampitec]

In D89599#2352063, @Paul-C-Anagnostopoulos wrote:

Yes, making the 0 and 1 unsigned fixes the problem.

Changed to 0U and 1U in ad8131bb03d0abd9e0586b9fa91d45cbf90ca83e.
This is a somewhat weird warning given strictly positive literals though.

[rampitec]

rG611959f004d78f99e45fdc940a7a4322b85d04d9

[Paul-C-Anagnostopoulos]

Yes, I was rather surprised about the warning, too. This is the first time I've seen it, though I've been working on LLVM for only a couple of months.

Thanks!

llvm/lib/Target/AMDGPU/SIShrinkInstructions.cpp

if (Reg.isPhysical()) {
       Sub = TRI.getSubRegFromChannel(I + TRI.getChannelFromSubReg(Sub));
     }
   }
   return TargetInstrInfo::RegSubRegPair(Reg, Sub);
 }
 
 // Match:
 // mov t, x
 // mov x, y
 // mov y, t
 //
 // =>
 //
 // mov t, x (t is potentially dead and move eliminated)
 // v_swap_b32 x, y
 //
 // Returns next valid instruction pointer if was able to create v_swap_b32.
 //
 // This shall not be done too early not to prevent possible folding which may
 // remove matched moves, and this should prefereably be done before RA to
 // release saved registers and also possibly after RA which can insert copies
 // too.
static MachineInstr* matchSwap(MachineInstr &MovT, MachineRegisterInfo &MRI,
   unsigned Xsub = Xop.getSubReg();
 
   unsigned Size = TII->getOpSize(MovT, 0) / 4;
 
   const SIRegisterInfo &TRI = TII->getRegisterInfo();
   if (!TRI.isVGPR(MRI, X))
     return nullptr;
 
+  // One implicit operand is EXEC, the rest we may want to preserve as the
+  // instruction will be killed if combined.
+  if (MovT.getNumImplicitOperands() > (MovT.isCopy() ? 0 : 1))
+    return nullptr;
+
   const unsigned SearchLimit = 16;
   unsigned Count = 0;
+  bool KilledT = false;
   for (auto Iter = std::next(MovT.getIterator()),
             E = MovT.getParent()->instr_end();
-       Iter != E && Count < SearchLimit; ++Iter, ++Count) {
+       Iter != E && Count < SearchLimit && !KilledT; ++Iter, ++Count) {
 
     MachineInstr *MovY = &*Iter;
+    KilledT = MovY->killsRegister(T, &TRI);
+
     if ((MovY->getOpcode() != AMDGPU::V_MOV_B32_e32 &&
          MovY->getOpcode() != AMDGPU::COPY) ||
         !MovY->getOperand(1).isReg()        ||
         MovY->getOperand(1).getReg() != T   ||
-        MovY->getOperand(1).getSubReg() != Tsub)
+        MovY->getOperand(1).getSubReg() != Tsub ||
+        MovY->getNumImplicitOperands() > (MovY->isCopy() ? 0 : 1))
       continue;
 
     Register Y = MovY->getOperand(0).getReg();
     unsigned Ysub = MovY->getOperand(0).getSubReg();
 
     if (!TRI.isVGPR(MRI, Y))
       continue;
 
for (auto IY = MovY->getIterator(), I = std::next(MovT.getIterator());
       if (MovX ||
           (I->getOpcode() != AMDGPU::V_MOV_B32_e32 &&
            I->getOpcode() != AMDGPU::COPY) ||
           I->getOperand(0).getReg() != X ||
           I->getOperand(0).getSubReg() != Xsub) {
         MovX = nullptr;
         break;
       }
+      if (I->getNumImplicitOperands() > (I->isCopy() ? 0 : 1))
+        continue;
+
       MovX = &*I;
     }
 
     if (!MovX)
       continue;
 
-    LLVM_DEBUG(dbgs() << "Matched v_swap_b32:\n" << MovT << *MovX << MovY);
+    LLVM_DEBUG(dbgs() << "Matched v_swap_b32:\n" << MovT << *MovX << *MovY);
 
     for (unsigned I = 0; I < Size; ++I) {
       TargetInstrInfo::RegSubRegPair X1, Y1;
       X1 = getSubRegForIndex(X, Xsub, I, TRI, MRI);
       Y1 = getSubRegForIndex(Y, Ysub, I, TRI, MRI);
       BuildMI(*MovT.getParent(), MovX->getIterator(), MovT.getDebugLoc(),
                 TII->get(AMDGPU::V_SWAP_B32))
         .addDef(X1.Reg, 0, X1.SubReg)

llvm/test/CodeGen/AMDGPU/v_swap_b32.mir

bb.0:
     %0 = IMPLICIT_DEF
     %1 = IMPLICIT_DEF
     %2 = COPY %0
     %0 = COPY %1
     %1 = COPY %2
 ...
 
 # GCN-LABEL: name: swap_virt_copy_subreg_impdef_super
-# GCN: %0.sub0:vreg_64, %1.sub0:vreg_64 = V_SWAP_B32 %1.sub0, %0.sub0, implicit $exec
+# GCN: %2.sub0:vreg_64 = COPY %0.sub0, implicit-def %2, implicit $exec
 ---
 name:            swap_virt_copy_subreg_impdef_super
 registers:
   - { id: 0, class: vreg_64 }
   - { id: 1, class: vreg_64 }
   - { id: 2, class: vreg_64 }
 body:             |
   bb.0:
bb.0:
     %4 = COPY %3
     %3 = COPY %4
     %4 = COPY %3
     %3 = COPY %4
     %0 = COPY %1
     %1 = COPY %2
     S_ENDPGM 0
 ...
+
+# GCN-LABEL: name: swap_liveness_error_mov
+# GCN:      $vgpr6 = V_MOV_B32_e32 $vgpr1, implicit $exec, implicit killed $vgpr1_vgpr2
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 killed $vgpr5, implicit $exec
+# GCN-NEXT: $vgpr5 = V_MOV_B32_e32 $vgpr6, implicit $exec, implicit-def $vgpr5_vgpr6, implicit $vgpr6_vgpr7
+# GCN-NEXT: $vgpr6 = V_MOV_B32_e32 $vgpr7, implicit $exec, implicit $vgpr6_vgpr7
+# GCN-NEXT: $vgpr5 = V_MOV_B32_e32 $vgpr6, implicit $exec
+
+---
+name: swap_liveness_error_mov
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr5, $vgpr1_vgpr2
+
+    $vgpr6 = V_MOV_B32_e32 $vgpr1, implicit $exec, implicit killed $vgpr1_vgpr2
+    $vgpr1 = V_MOV_B32_e32 killed $vgpr5, implicit $exec
+    $vgpr5 = V_MOV_B32_e32 $vgpr6, implicit $exec, implicit-def $vgpr5_vgpr6, implicit $vgpr6_vgpr7
+    $vgpr6 = V_MOV_B32_e32 $vgpr7, implicit $exec, implicit $vgpr6_vgpr7
+    $vgpr5 = V_MOV_B32_e32 $vgpr6, implicit $exec
+    S_ENDPGM 0
+...
+
+# GCN-LABEL: name: swap_liveness_error_copy
+# GCN:      $vgpr6 = COPY $vgpr1, implicit killed $vgpr1_vgpr2
+# GCN-NEXT: $vgpr1 = COPY killed $vgpr5
+# GCN-NEXT: $vgpr5 = COPY $vgpr6, implicit-def $vgpr5_vgpr6, implicit $vgpr6_vgpr7
+# GCN-NEXT: $vgpr6 = COPY $vgpr7, implicit $vgpr6_vgpr7
+# GCN-NEXT: $vgpr5 = COPY $vgpr6
+
+---
+name: swap_liveness_error_copy
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr5, $vgpr1_vgpr2
+
+    $vgpr6 = COPY $vgpr1, implicit killed $vgpr1_vgpr2
+    $vgpr1 = COPY killed $vgpr5
+    $vgpr5 = COPY $vgpr6, implicit-def $vgpr5_vgpr6, implicit $vgpr6_vgpr7
+    $vgpr6 = COPY $vgpr7, implicit $vgpr6_vgpr7
+    $vgpr5 = COPY $vgpr6
+    S_ENDPGM 0
+...
+
+# GCN-LABEL: name: swap_killed_t_early
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+# GCN-NEXT: $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec, implicit killed $vgpr2
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+# GCN-NEXT: $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 undef $vgpr2, implicit $exec
+
+---
+name:            swap_killed_t_early
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+    $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec, implicit killed $vgpr2
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+    $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec
+    $vgpr1 = V_MOV_B32_e32 undef $vgpr2, implicit $exec
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...
+
+# GCN-LABEL: name: swap_killed_t_late
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+# GCN-NEXT: $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+# GCN-NEXT: $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec, implicit killed $vgpr2
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 undef $vgpr2, implicit $exec
+
+---
+name:            swap_killed_t_late
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+    $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+    $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec, implicit killed $vgpr2
+    $vgpr1 = V_MOV_B32_e32 undef $vgpr2, implicit $exec
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...
+
+# GCN-LABEL: name: swap_killed_x
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+# GCN-NEXT: $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+# GCN-NEXT: $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec, implicit killed $vgpr0
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+
+---
+name:            swap_killed_x
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+    $vgpr3 = V_MOV_B32_e32 killed $vgpr4, implicit $exec
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+    $vgpr5 = V_MOV_B32_e32 killed $vgpr6, implicit $exec, implicit killed $vgpr0
+    $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...
+
+# GCN-LABEL: name: indirect_mov_t
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec, implicit $m0
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+# GCN-NEXT: S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+
+---
+name:            indirect_mov_t
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec, implicit $m0
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+    $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...
+
+# GCN-LABEL: name: indirect_mov_x
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec, implicit $m0
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+# GCN-NEXT: S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+
+---
+name:            indirect_mov_x
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec, implicit $m0
+    $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...
+
+# GCN-LABEL: name: indirect_mov_y
+# GCN:      $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+# GCN-NEXT: $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec, implicit $m0
+# GCN-NEXT: S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+
+---
+name:            indirect_mov_y
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $sgpr30_sgpr31
+    $vgpr2 = V_MOV_B32_e32 killed $vgpr0, implicit $exec
+    $vgpr0 = V_MOV_B32_e32 killed $vgpr1, implicit $exec
+    $vgpr1 = V_MOV_B32_e32 killed $vgpr2, implicit $exec, implicit $m0
+    S_SETPC_B64_return $sgpr30_sgpr31, implicit $vgpr0, implicit $vgpr1
+...