AMDGPU: Move m0 initializations earlier

[kerbowa]

Summary

After hoisting and merging m0 initializations schedule them as early as
possible in the MBB. This helps the scheduler avoid hazards in some
cases.

[kerbowa]

Fix test.

[rampitec]

llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp

614

Pass TRI into these two calls.

[kerbowa]

Add TRI to reads/definesRegsiter.

[rampitec]

LGTM

llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp

static bool hoistAndMergeSGPRInits(unsigned Reg,
   SmallVector<MachineInstr*, 8> Clobbers;
   // List of instructions marked for deletion.
   SmallSet<MachineInstr*, 8> MergedInstrs;
 
   bool Changed = false;
 
   for (auto &MI : MRI.def_instructions(Reg)) {
     MachineOperand *Imm = nullptr;
-    for (auto &MO: MI.operands()) {
+    for (auto &MO : MI.operands()) {
       if ((MO.isReg() && ((MO.isDef() && MO.getReg() != Reg) || !MO.isDef())) ||
           (!MO.isImm() && !MO.isReg()) || (MO.isImm() && Imm)) {
         Imm = nullptr;
         break;
       } else if (MO.isImm())
         Imm = &MO;
     }
     if (Imm)
for (auto I1 = Defs.begin(), E = Defs.end(); I1 != E; ) {
           }
         }
         ++I2;
       }
       ++I1;
     }
   }
 
-  for (auto MI : MergedInstrs)
-    MI->removeFromParent();
+  // Remove initializations that were merged into another.
+  for (auto &Init : Inits) {
+    auto &Defs = Init.second;
+    for (auto I = Defs.begin(); I != Defs.end(); ++I)
+      if (MergedInstrs.count(*I)) {
+        (*I)->eraseFromParent();
+        I = Defs.erase(I);
+      }
+  }
+
+  // Try to schedule SGPR initializations as early as possible in the MBB.
+  for (auto &Init : Inits) {
+    auto &Defs = Init.second;
+    for (auto MI : Defs) {
+      auto MBB = MI->getParent();
+      MachineInstr &BoundaryMI = *getFirstNonPrologue(MBB, TII);
+      MachineBasicBlock::reverse_iterator B(BoundaryMI);
+      // Check if B should actually be a bondary. If not set the previous
+      // instruction as the boundary instead.
+      if (!TII->isBasicBlockPrologue(*B))
+        B++;
+
+      auto R = std::next(MI->getReverseIterator());
+      const unsigned Threshold = 50;
+      // Search until B or Threashold for a place to insert the initialization.
+      for (unsigned I = 0; R != B && I < Threshold; ++R, ++I)
+        if (R->readsRegister(Reg) || R->definesRegister(Reg) ||
+            TII->isSchedulingBoundary(*R, MBB, *MBB->getParent()))
+          break;
+
+      // Move to directly after R.
+      if (&*--R != MI)
+        MBB->splice(*R, MBB, MI);
+    }
+  }
 
   if (Changed)
     MRI.clearKillFlags(Reg);
 
   return Changed;
 }
 
 bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) {

llvm/test/CodeGen/AMDGPU/frame-index-elimination.ll

 }
 
 ; Offset due to different objects
 ; GCN-LABEL: {{^}}func_mov_fi_i32_offset:
 ; GCN: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 
 ; CI: s_sub_u32 [[SUB0:s[0-9]+|vcc_lo|vcc_hi]], s32, s33
 ; CI-NEXT: s_sub_u32 [[SUB1:s[0-9]+|vcc_lo|vcc_hi]], s32, s33
-; CI-NEXT: v_lshr_b32_e64 [[SCALED:v[0-9]+]], [[SUB1]], 6
-; CI-NEXT: v_lshr_b32_e64 v0, [[SUB0]], 6
-; CI-NEXT: v_add_i32_e64 v1, s{{\[[0-9]+:[0-9]+\]}}, 4, [[SCALED]]
+; CI-DAG: v_lshr_b32_e64 v0, [[SUB0]], 6
+; CI-DAG: v_lshr_b32_e64 [[SCALED:v[0-9]+]], [[SUB1]], 6
 ; CI-NOT: v_mov
 ; CI: ds_write_b32 v0, v0
-; CI-NEXT: ds_write_b32 v0, v1
+; CI-NEXT: v_add_i32_e64 v0, s{{\[[0-9]+:[0-9]+\]}}, 4, [[SCALED]]
+; CI-NEXT: ds_write_b32 v0, v0
 
 ; GFX9: s_sub_u32 [[SUB0:s[0-9]+|vcc_lo|vcc_hi]], s32, s33
 ; GFX9-NEXT: s_sub_u32 [[SUB1:s[0-9]+|vcc_lo|vcc_hi]], s32, s33
 ; GFX9-NEXT: v_lshrrev_b32_e64 v0, 6, [[SUB0]]
 ; GFX9-NEXT: v_lshrrev_b32_e64 [[SCALED:v[0-9]+]], 6, [[SUB1]]
 ; GFX9-DAG: ds_write_b32 v0, v0
 ; GFX9-NEXT: v_add_u32_e32 v0, 4, [[SCALED]]
 ; GFX9-NEXT: ds_write_b32 v0, v0

llvm/test/CodeGen/AMDGPU/merge-m0.mir

 # RUN: llc -march=amdgcn -amdgpu-enable-merge-m0 -verify-machineinstrs -run-pass si-fix-sgpr-copies %s -o - | FileCheck -check-prefix=GCN %s
 
+# GCN-LABEL: name: merge-m0-many-init
 # GCN:    bb.0.entry:
 # GCN:      SI_INIT_M0 -1
+# GCN-NEXT: IMPLICIT_DEF
+# GCN-NEXT: IMPLICIT_DEF
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: SI_INIT_M0 65536
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: SI_INIT_M0 -1
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: SI_INIT_M0 65536

 # GCN:      SI_INIT_M0 -1,
 # GCN-NEXT: DS_WRITE_B32
 # GCN:      SI_INIT_M0 %2
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: SI_INIT_M0 %2
 # GCN-NEXT: DS_WRITE_B32
 # GCN-NEXT: SI_INIT_M0 -1
 # GCN-NEXT: DS_WRITE_B32
-
 ---
-name:            merge-m0-many-init
+name: merge-m0-many-init
 registers:
   - { id: 0, class: vgpr_32 }
   - { id: 1, class: vgpr_32 }
   - { id: 2, class: sreg_32_xm0 }
 body:             |
   bb.0.entry:
     successors: %bb.1, %bb.2
 
bb.6:
     DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
     SI_INIT_M0 -1, implicit-def $m0
     DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
     S_CBRANCH_VCCZ %bb.6, implicit undef $vcc
     S_BRANCH %bb.0.entry
 
 ...
 
+# GCN-LABEL: name: merge-m0-dont-hoist-past-init-with-different-initializer
 # GCN:    bb.0.entry:
 # GCN:      SI_INIT_M0 65536
+# GCN-NEXT: IMPLICIT_DEF
+# GCN-NEXT: IMPLICIT_DEF
 # GCN-NEXT: DS_WRITE_B32
 
-#GCN:     bb.1:
-#GCN-NOT:   SI_INIT_M0 65536
-#GCN-NOT:   SI_INIT_M0 -1
+# GCN:    bb.1:
+# GCN-NOT:  SI_INIT_M0 65536
+# GCN-NOT:  SI_INIT_M0 -1
 
-#GCN:     bb.2:
-#GCN:       SI_INIT_M0 -1
+# GCN:    bb.2:
+# GCN:      SI_INIT_M0 -1
 
-#GCN:     bb.3:
-#GCN:       SI_INIT_M0 -1
-
+# GCN:    bb.3:
+# GCN:      SI_INIT_M0 -1
 ---
-name:            merge-m0-dont-hoist-past-init-with-different-initializer
+name: merge-m0-dont-hoist-past-init-with-different-initializer
 registers:
   - { id: 0, class: vgpr_32 }
   - { id: 1, class: vgpr_32 }
 body:             |
   bb.0.entry:
     successors: %bb.1
 
     %0 = IMPLICIT_DEF
bb.3:
     SI_INIT_M0 -1, implicit-def $m0
     DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
     S_BRANCH %bb.4
 
   bb.4:
     S_ENDPGM 0
 ...
 
+# GCN-LABEL: name: merge-m0-after-prologue
 # GCN:    bb.0.entry:
 # GCN-NOT:  SI_INIT_M0
 # GCN:      S_OR_B64
 # GCN-NEXT: SI_INIT_M0
 
-#GCN:     bb.1:
-#GCN-NOT:   SI_INIT_M0 -1
+# GCN:     bb.1:
+# GCN-NOT:   SI_INIT_M0 -1
 
-#GCN:     bb.2:
-#GCN-NOT:   SI_INIT_MO -1
-
+# GCN:     bb.2:
+# GCN-NOT:   SI_INIT_MO -1
 ---
-name:            merge-m0-after-prologue
+name: merge-m0-after-prologue
 registers:
   - { id: 0, class: vgpr_32 }
   - { id: 1, class: vgpr_32 }
 body:             |
   bb.0.entry:
     successors: %bb.1, %bb.2
     liveins: $sgpr0_sgpr1
 
bb.2:
 
     SI_INIT_M0 -1, implicit-def $m0
     DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
     S_BRANCH %bb.3
 
   bb.3:
     S_ENDPGM 0
 ...
+
+# GCN-LABEL: name: move-m0-avoid-hazard
+# GCN: $m0 = S_MOV_B32 -1
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 0, implicit $exec
+# GCN-NEXT: DS_GWS_INIT $vgpr0, 0, 1, implicit $m0, implicit $exec
+---
+name: move-m0-avoid-hazard
+body:             |
+  bb.0:
+    $vgpr0 = V_MOV_B32_e32 0, implicit $exec
+    $m0 = S_MOV_B32 -1
+    DS_GWS_INIT $vgpr0, 0, 1, implicit $m0, implicit $exec
+...
+
+# GCN-LABEL: name: move-m0-with-prologue
+# GCN $exec = S_OR_B64 $exec, killed $sgpr0_sgpr1, implicit-def $scc
+# GCN: $m0 = S_MOV_B32 -1
+# GCN-NEXT: $vgpr0 = V_MOV_B32_e32 0, implicit $exec
+# GCN-NEXT: DS_GWS_INIT $vgpr0, 0, 1, implicit $m0, implicit $exec
+---
+name: move-m0-with-prologue
+body:             |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    $exec = S_OR_B64 $exec, killed $sgpr0_sgpr1, implicit-def $scc
+    $vgpr0 = V_MOV_B32_e32 0, implicit $exec
+    $m0 = S_MOV_B32 -1
+    DS_GWS_INIT $vgpr0, 0, 1, implicit $m0, implicit $exec
+...
+
+# GCN-LABEL: name: move-m0-different-initializer
+# GCN: SI_INIT_M0 -1
+# GCN-NEXT: %0:vgpr_32 = IMPLICIT_DEF
+# GCN: SI_INIT_M0 65536
+# GCN-NEXT: S_NOP
+---
+name: move-m0-different-initializer
+registers:
+  - { id: 0, class: vgpr_32 }
+  - { id: 1, class: vgpr_32 }
+body:             |
+  bb.0:
+    %0 = IMPLICIT_DEF
+    %1 = IMPLICIT_DEF
+    SI_INIT_M0 -1, implicit-def $m0
+    DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
+    S_NOP 0
+    SI_INIT_M0 65536, implicit-def $m0
+    DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
+...
+
+# GCN-LABEL: name: move-m0-schedule-boundary
+# GCN: S_SETREG
+# GCN-NEXT: SI_INIT_M0 -1
+---
+name: move-m0-schedule-boundary
+body:             |
+  bb.0:
+    S_NOP 0
+    S_SETREG_IMM32_B32 0, 1
+    SI_INIT_M0 -1, implicit-def $m0
+    DS_WRITE_B32 %0, %1, 0, 0, implicit $m0, implicit $exec
+...