[ARM][LowOverheadLoops] Merge VCMP and VPST across VPT blocks

This patch adds support for combining a VPST with a dangling VCMP from a
previous VPT block.

Differential Revision: https://reviews.llvm.org/D90935

llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp

@@ -87,8 +87,8 @@ static bool isVectorPredicate(MachineInstr *MI) {
   return MI->findRegisterDefOperandIdx(ARM::VPR) != -1;
 }
 
-static bool hasVPRUse(MachineInstr *MI) {
+static bool hasVPRUse(MachineInstr &MI) {
-  return MI->findRegisterUseOperandIdx(ARM::VPR) != -1;
+  return MI.findRegisterUseOperandIdx(ARM::VPR) != -1;
 }
 
 static bool isDomainMVE(MachineInstr *MI) {
@@ -97,8 +97,7 @@ static bool isDomainMVE(MachineInstr *MI) {
 }
 
 static bool shouldInspect(MachineInstr &MI) {
-  return isDomainMVE(&MI) || isVectorPredicate(&MI) ||
+  return isDomainMVE(&MI) || isVectorPredicate(&MI) || hasVPRUse(MI);
-    hasVPRUse(&MI);
 }
 
 static bool isDo(MachineInstr *MI) {
@@ -1485,14 +1484,33 @@ void ARMLowOverheadLoops::ConvertVPTBlocks(LowOverheadLoop &LoLoop) {
   for (auto &Block : LoLoop.getVPTBlocks()) {
     SmallVectorImpl<MachineInstr *> &Insts = Block.getInsts();
 
-    if (VPTState::isEntryPredicatedOnVCTP(Block, /*exclusive*/true)) {
+    auto ReplaceVCMPWithVPT = [&](MachineInstr *&TheVCMP, MachineInstr *At) {
+      assert(TheVCMP && "Replacing a removed or non-existent VCMP");
+      // Replace the VCMP with a VPT
+      MachineInstrBuilder MIB =
+          BuildMI(*At->getParent(), At, At->getDebugLoc(),
+                  TII->get(VCMPOpcodeToVPT(TheVCMP->getOpcode())));
+      MIB.addImm(ARMVCC::Then);
+      // Register one
+      MIB.add(TheVCMP->getOperand(1));
+      // Register two
+      MIB.add(TheVCMP->getOperand(2));
+      // The comparison code, e.g. ge, eq, lt
+      MIB.add(TheVCMP->getOperand(3));
+      LLVM_DEBUG(dbgs() << "ARM Loops: Combining with VCMP to VPT: " << *MIB);
+      LoLoop.BlockMasksToRecompute.insert(MIB.getInstr());
+      LoLoop.ToRemove.insert(TheVCMP);
+      TheVCMP = nullptr;
+    };
+
+    if (VPTState::isEntryPredicatedOnVCTP(Block, /*exclusive*/ true)) {
+      MachineInstr *VPST = Insts.front();
       if (VPTState::hasUniformPredicate(Block)) {
         // A vpt block starting with VPST, is only predicated upon vctp and has no
         // internal vpr defs:
         // - Remove vpst.
         // - Unpredicate the remaining instructions.
-        LLVM_DEBUG(dbgs() << "ARM Loops: Removing VPST: " << *Insts.front());
+        LLVM_DEBUG(dbgs() << "ARM Loops: Removing VPST: " << *VPST);
-        LoLoop.ToRemove.insert(Insts.front());
         for (unsigned i = 1; i < Insts.size(); ++i)
           RemovePredicate(Insts[i]);
       } else {
@@ -1503,10 +1521,7 @@ void ARMLowOverheadLoops::ConvertVPTBlocks(LowOverheadLoop &LoLoop) {
         //   we come across the divergent vpr def.
         // - Insert a new vpst to predicate the instruction(s) that following
         //   the divergent vpr def.
-        // TODO: We could be producing more VPT blocks than necessary and could
-        // fold the newly created one into a proceeding one.
         MachineInstr *Divergent = VPTState::getDivergent(Block);
-        MachineInstr *VPST = Insts.front();
         auto DivergentNext = ++MachineBasicBlock::iterator(Divergent);
         bool DivergentNextIsPredicated =
             getVPTInstrPredicate(*DivergentNext) != ARMVCC::None;
@@ -1520,24 +1535,6 @@ void ARMLowOverheadLoops::ConvertVPTBlocks(LowOverheadLoop &LoLoop) {
         MachineInstr *VCMP =
             VCMPOpcodeToVPT(Divergent->getOpcode()) != 0 ? Divergent : nullptr;
 
-        auto ReplaceVCMPWithVPT = [&]() {
-          // Replace the VCMP with a VPT
-          MachineInstrBuilder MIB = BuildMI(
-              *Divergent->getParent(), Divergent, Divergent->getDebugLoc(),
-              TII->get(VCMPOpcodeToVPT(VCMP->getOpcode())));
-          MIB.addImm(ARMVCC::Then);
-          // Register one
-          MIB.add(VCMP->getOperand(1));
-          // Register two
-          MIB.add(VCMP->getOperand(2));
-          // The comparison code, e.g. ge, eq, lt
-          MIB.add(VCMP->getOperand(3));
-          LLVM_DEBUG(dbgs()
-                     << "ARM Loops: Combining with VCMP to VPT: " << *MIB);
-          LoLoop.BlockMasksToRecompute.insert(MIB.getInstr());
-          LoLoop.ToRemove.insert(VCMP);
-        };
-
         if (DivergentNextIsPredicated) {
           // Insert a VPST at the divergent only if the next instruction
           // would actually use it. A VCMP following a VPST can be
@@ -1553,17 +1550,48 @@ void ARMLowOverheadLoops::ConvertVPTBlocks(LowOverheadLoop &LoLoop) {
             LoLoop.BlockMasksToRecompute.insert(MIB.getInstr());
           } else {
             // No RDA checks are necessary here since the VPST would have been
-            // directly before the VCMP
+            // directly after the VCMP
-            ReplaceVCMPWithVPT();
+            ReplaceVCMPWithVPT(VCMP, VCMP);
           }
         }
-        LLVM_DEBUG(dbgs() << "ARM Loops: Removing VPST: " << *VPST);
-        LoLoop.ToRemove.insert(VPST);
       }
+      LLVM_DEBUG(dbgs() << "ARM Loops: Removing VPST: " << *VPST);
+      LoLoop.ToRemove.insert(VPST);
     } else if (Block.containsVCTP()) {
       // The vctp will be removed, so the block mask of the vp(s)t will need
       // to be recomputed.
       LoLoop.BlockMasksToRecompute.insert(Insts.front());
+    } else if (Insts.front()->getOpcode() == ARM::MVE_VPST) {
+      // If this block starts with a VPST then attempt to merge it with the
+      // preceeding un-merged VCMP into a VPT. This VCMP comes from a VPT
+      // block that no longer exists
+      MachineInstr *VPST = Insts.front();
+      auto Next = ++MachineBasicBlock::iterator(VPST);
+      assert(getVPTInstrPredicate(*Next) != ARMVCC::None &&
+             "The instruction after a VPST must be predicated");
+
+      MachineInstr *VprDef = RDA->getUniqueReachingMIDef(VPST, ARM::VPR);
+      if (VprDef && VCMPOpcodeToVPT(VprDef->getOpcode()) &&
+          !LoLoop.ToRemove.contains(VprDef)) {
+        MachineInstr *VCMP = VprDef;
+        // The VCMP and VPST can only be merged if the VCMP's operands will have
+        // the same values at the VPST
+        if (RDA->hasSameReachingDef(VCMP, VPST, VCMP->getOperand(1).getReg()) &&
+            RDA->hasSameReachingDef(VCMP, VPST, VCMP->getOperand(2).getReg())) {
+          bool IntermediateInstrsUseVPR =
+              std::any_of(++MachineBasicBlock::iterator(VCMP),
+                          MachineBasicBlock::iterator(VPST), hasVPRUse);
+          // If the instruction after the VCMP is predicated then a different
+          // code path is expected to have merged the VCMP and VPST already.
+          // This assertion protects against changes to that behaviour
+          assert(!IntermediateInstrsUseVPR &&
+                 "Instructions between the VCMP and VPST are not expected to "
+                 "be predicated");
+          ReplaceVCMPWithVPT(VCMP, VPST);
+          LLVM_DEBUG(dbgs() << "ARM Loops: Removing VPST: " << *VPST);
+          LoLoop.ToRemove.insert(VPST);
+        }
+      }
     }
   }
 

llvm/test/CodeGen/Thumb2/LowOverheadLoops/vcmp-vpst-combination-across-blocks.mir

@@ -0,0 +1,479 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=thumbv8.1m.main -mattr=+mve -run-pass=arm-low-overhead-loops %s -o - --verify-machineinstrs | FileCheck %s
+
+--- |
+  define void @combine_previous() {
+  while.end6:
+    ret void
+  }
+
+  define void @combine_middle() {
+  while.end6:
+    ret void
+  }
+
+  define void @combine_last() {
+  while.end6:
+    ret void
+  }
+
+  define void @no_combination_diff_reg_value() {
+  while.end6:
+    ret void
+  }
+
+  define void @no_combination_vcmp_already_merged() {
+  while.end6:
+    ret void
+  }
+
+...
+---
+name:            combine_previous
+alignment:       8
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+  - { reg: '$r2', virtual-reg: '' }
+frameInfo:
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:
+  - id:              0
+    value:           float 0xC7EFFFFFE0000000
+    alignment:       4
+    isTargetSpecific: false
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: combine_previous
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $r0, $r1
+  ; CHECK:   renamable $q0 = MVE_VDUP32 renamable $r1, 0, $noreg, undef renamable $q0
+  ; CHECK:   $lr = MVE_DLSTP_32 killed renamable $r1
+  ; CHECK: bb.1 (align 4):
+  ; CHECK:   successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+  ; CHECK:   liveins: $lr, $q0, $r0
+  ; CHECK:   renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 0, $noreg
+  ; CHECK:   renamable $q0 = MVE_VORR renamable $q1, renamable $q1, 0, $noreg, killed renamable $q0
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q1, renamable $q0, 12, implicit-def $vpr
+  ; CHECK:   renamable $q0 = MVE_VORR killed renamable $q1, killed renamable $q1, 1, killed renamable $vpr, killed renamable $q0
+  ; CHECK:   $lr = MVE_LETP killed renamable $lr, %bb.1
+  ; CHECK: bb.2:
+  ; CHECK:   frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+  ; CHECK: bb.3 (align 4):
+  ; CHECK:   CONSTPOOL_ENTRY 0, %const.0, 4
+  bb.0:
+    successors: %bb.6(0x80000000)
+    liveins: $r0, $r1, $r2
+
+    renamable $r3, dead $cpsr = nuw nsw tADDi3 renamable $r1, 3, 14 /* CC::al */, $noreg
+    renamable $q0 = MVE_VDUP32 killed renamable $r1, 0, $noreg, undef renamable $q0
+    renamable $r3 = t2ANDri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $lr = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
+    renamable $lr = nuw nsw t2ADDrs killed renamable $r3, killed renamable $lr, 19, 14 /* CC::al */, $noreg, $noreg
+    $lr = t2DoLoopStart renamable $lr
+
+  bb.6 (align 4):
+    successors: %bb.6(0x7c000000), %bb.8(0x04000000)
+    liveins: $lr, $q0, $r0, $r1, $r2
+
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    renamable $vpr = MVE_VCTP32 renamable $r1, 0, $noreg
+    renamable $r1, dead $cpsr = tSUBi8 killed renamable $r1, 4, 14 /* CC::al */, $noreg
+    MVE_VPST 8, implicit $vpr
+    renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 1, renamable $vpr
+    MVE_VPST 4, implicit $vpr
+    renamable $q0 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, renamable $q0
+    renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 1, killed renamable $vpr
+    MVE_VPST 8, implicit $vpr
+    renamable $q0 = MVE_VORR killed renamable $q1, renamable $q1, 1, killed renamable $vpr, killed renamable $q0
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.8, 14 /* CC::al */, $noreg
+
+  bb.8:
+    liveins: $r2, $r12, $q0
+    frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+  bb.9 (align 4):
+    CONSTPOOL_ENTRY 0, %const.0, 4
+
+...
+---
+name:            combine_middle
+alignment:       8
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+  - { reg: '$r2', virtual-reg: '' }
+frameInfo:
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:
+  - id:              0
+    value:           float 0xC7EFFFFFE0000000
+    alignment:       4
+    isTargetSpecific: false
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: combine_middle
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $q2, $r0, $r1
+  ; CHECK:   renamable $q0 = MVE_VDUP32 renamable $r1, 0, $noreg, undef renamable $q0
+  ; CHECK:   $lr = MVE_DLSTP_32 killed renamable $r1
+  ; CHECK: bb.1 (align 4):
+  ; CHECK:   successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+  ; CHECK:   liveins: $lr, $q0, $q2, $r0
+  ; CHECK:   renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 0, $noreg
+  ; CHECK:   renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 0, $noreg, killed renamable $q2
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q1, renamable $q0, 12, implicit-def $vpr
+  ; CHECK:   renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+  ; CHECK:   MVE_VPST 4, implicit $vpr
+  ; CHECK:   dead renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, killed renamable $vpr, killed renamable $q1
+  ; CHECK:   $lr = MVE_LETP killed renamable $lr, %bb.1
+  ; CHECK: bb.2:
+  ; CHECK:   frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+  ; CHECK: bb.3 (align 4):
+  ; CHECK:   CONSTPOOL_ENTRY 0, %const.0, 4
+  bb.0:
+    successors: %bb.6(0x80000000)
+    liveins: $r0, $r1, $r2
+
+    renamable $r3, dead $cpsr = nuw nsw tADDi3 renamable $r1, 3, 14 /* CC::al */, $noreg
+    renamable $q0 = MVE_VDUP32 killed renamable $r1, 0, $noreg, undef renamable $q0
+    renamable $r3 = t2ANDri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $lr = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
+    renamable $lr = nuw nsw t2ADDrs killed renamable $r3, killed renamable $lr, 19, 14 /* CC::al */, $noreg, $noreg
+    $lr = t2DoLoopStart renamable $lr
+
+  bb.6 (align 4):
+    successors: %bb.6(0x7c000000), %bb.8(0x04000000)
+    liveins: $lr, $q0, $r0, $r1, $r2, $q2
+
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    renamable $vpr = MVE_VCTP32 renamable $r1, 0, $noreg
+    renamable $r1, dead $cpsr = tSUBi8 killed renamable $r1, 4, 14 /* CC::al */, $noreg
+    MVE_VPST 2, implicit $vpr
+    renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 1, renamable $vpr
+    renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+    renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 1, killed renamable $vpr
+    MVE_VPST 8, implicit $vpr
+    renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+    MVE_VPST 4, implicit $vpr
+    renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, renamable $vpr, renamable $q1
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.8, 14 /* CC::al */, $noreg
+
+  bb.8:
+    liveins: $r2, $r12, $q0
+    frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+  bb.9 (align 4):
+    CONSTPOOL_ENTRY 0, %const.0, 4
+
+...
+---
+name:            combine_last
+alignment:       8
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+  - { reg: '$r2', virtual-reg: '' }
+frameInfo:
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:
+  - id:              0
+    value:           float 0xC7EFFFFFE0000000
+    alignment:       4
+    isTargetSpecific: false
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: combine_last
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $q2, $r0, $r1
+  ; CHECK:   renamable $q0 = MVE_VDUP32 renamable $r1, 0, $noreg, undef renamable $q0
+  ; CHECK:   $lr = MVE_DLSTP_32 killed renamable $r1
+  ; CHECK: bb.1 (align 4):
+  ; CHECK:   successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+  ; CHECK:   liveins: $lr, $q0, $q2, $r0
+  ; CHECK:   renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 0, $noreg
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q1, renamable $q0, 12, implicit-def $vpr
+  ; CHECK:   renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, killed renamable $vpr, killed renamable $q2
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q2, renamable $q1, 12, implicit-def $vpr
+  ; CHECK:   dead renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, killed renamable $vpr, killed renamable $q1
+  ; CHECK:   $lr = MVE_LETP killed renamable $lr, %bb.1
+  ; CHECK: bb.2:
+  ; CHECK:   frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+  ; CHECK: bb.3 (align 4):
+  ; CHECK:   CONSTPOOL_ENTRY 0, %const.0, 4
+  bb.0:
+    successors: %bb.6(0x80000000)
+    liveins: $r0, $r1, $r2
+
+    renamable $r3, dead $cpsr = nuw nsw tADDi3 renamable $r1, 3, 14 /* CC::al */, $noreg
+    renamable $q0 = MVE_VDUP32 killed renamable $r1, 0, $noreg, undef renamable $q0
+    renamable $r3 = t2ANDri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $lr = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
+    renamable $lr = nuw nsw t2ADDrs killed renamable $r3, killed renamable $lr, 19, 14 /* CC::al */, $noreg, $noreg
+    $lr = t2DoLoopStart renamable $lr
+
+  bb.6 (align 4):
+    successors: %bb.6(0x7c000000), %bb.8(0x04000000)
+    liveins: $lr, $q0, $r0, $r1, $r2, $q2
+
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    renamable $vpr = MVE_VCTP32 renamable $r1, 0, $noreg
+    renamable $r1, dead $cpsr = tSUBi8 killed renamable $r1, 4, 14 /* CC::al */, $noreg
+    MVE_VPST 8, implicit $vpr
+    renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 1, renamable $vpr
+    MVE_VPST 2, implicit $vpr
+    renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 1, killed renamable $vpr
+    renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+    renamable $vpr = MVE_VCMPf32 renamable $q2, renamable $q1, 12, 1, killed renamable $vpr
+    MVE_VPST 8, implicit $vpr
+    renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, renamable $vpr, renamable $q1
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.8, 14 /* CC::al */, $noreg
+
+  bb.8:
+    liveins: $r2, $r12, $q0
+    frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+  bb.9 (align 4):
+    CONSTPOOL_ENTRY 0, %const.0, 4
+
+...
+---
+name:            no_combination_diff_reg_value
+alignment:       8
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+  - { reg: '$r2', virtual-reg: '' }
+frameInfo:
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:
+  - id:              0
+    value:           float 0xC7EFFFFFE0000000
+    alignment:       4
+    isTargetSpecific: false
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: no_combination_diff_reg_value
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $r0, $r1
+  ; CHECK:   renamable $q0 = MVE_VDUP32 renamable $r1, 0, $noreg, undef renamable $q0
+  ; CHECK:   $lr = MVE_DLSTP_32 killed renamable $r1
+  ; CHECK: bb.1 (align 4):
+  ; CHECK:   successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+  ; CHECK:   liveins: $lr, $q0, $r0
+  ; CHECK:   renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 0, $noreg
+  ; CHECK:   renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 0, $noreg, killed renamable $q1
+  ; CHECK:   renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 0, killed $noreg
+  ; CHECK:   renamable $q0 = MVE_VORR renamable $q1, renamable $q1, 0, $noreg, killed renamable $q0
+  ; CHECK:   MVE_VPST 8, implicit $vpr
+  ; CHECK:   renamable $q0 = MVE_VORR killed renamable $q1, killed renamable $q1, 1, killed renamable $vpr, killed renamable $q0
+  ; CHECK:   $lr = MVE_LETP killed renamable $lr, %bb.1
+  ; CHECK: bb.2:
+  ; CHECK:   frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+  ; CHECK: bb.3 (align 4):
+  ; CHECK:   CONSTPOOL_ENTRY 0, %const.0, 4
+  bb.0:
+    successors: %bb.6(0x80000000)
+    liveins: $r0, $r1, $r2
+
+    renamable $r3, dead $cpsr = nuw nsw tADDi3 renamable $r1, 3, 14 /* CC::al */, $noreg
+    renamable $q0 = MVE_VDUP32 killed renamable $r1, 0, $noreg, undef renamable $q0
+    renamable $r3 = t2ANDri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $lr = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
+    renamable $lr = nuw nsw t2ADDrs killed renamable $r3, killed renamable $lr, 19, 14 /* CC::al */, $noreg, $noreg
+    $lr = t2DoLoopStart renamable $lr
+
+  bb.6 (align 4):
+    successors: %bb.6(0x7c000000), %bb.8(0x04000000)
+    liveins: $lr, $q0, $r0, $r1, $r2
+
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    renamable $vpr = MVE_VCTP32 renamable $r1, 0, $noreg
+    renamable $r1, dead $cpsr = tSUBi8 killed renamable $r1, 4, 14 /* CC::al */, $noreg
+    MVE_VPST 8, implicit $vpr
+    renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 1, renamable $vpr
+    MVE_VPST 4, implicit $vpr
+    renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, renamable $vpr, renamable $q1
+    renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 1, killed renamable $vpr
+    renamable $q0 = MVE_VORR renamable $q1, renamable $q1, 0, $noreg, killed renamable $q0
+    MVE_VPST 8, implicit $vpr
+    renamable $q0 = MVE_VORR killed renamable $q1, renamable $q1, 1, killed renamable $vpr, killed renamable $q0
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.8, 14 /* CC::al */, $noreg
+
+  bb.8:
+    liveins: $r2, $r12, $q0
+    frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+  bb.9 (align 4):
+    CONSTPOOL_ENTRY 0, %const.0, 4
+
+...
+---
+name:            no_combination_vcmp_already_merged
+alignment:       8
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+  - { reg: '$r2', virtual-reg: '' }
+frameInfo:
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:
+  - id:              0
+    value:           float 0xC7EFFFFFE0000000
+    alignment:       4
+    isTargetSpecific: false
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: no_combination_vcmp_already_merged
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $q2, $r0, $r1
+  ; CHECK:   renamable $q0 = MVE_VDUP32 renamable $r1, 0, $noreg, undef renamable $q0
+  ; CHECK:   $lr = MVE_DLSTP_32 killed renamable $r1
+  ; CHECK: bb.1 (align 4):
+  ; CHECK:   successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+  ; CHECK:   liveins: $lr, $q0, $q2, $r0
+  ; CHECK:   renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 0, $noreg
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q1, renamable $q0, 12, implicit-def $vpr
+  ; CHECK:   renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+  ; CHECK:   MVE_VPST 8, implicit $vpr
+  ; CHECK:   dead renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, killed renamable $vpr, killed renamable $q1
+  ; CHECK:   $lr = MVE_LETP killed renamable $lr, %bb.1
+  ; CHECK: bb.2:
+  ; CHECK:   frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+  ; CHECK: bb.3 (align 4):
+  ; CHECK:   CONSTPOOL_ENTRY 0, %const.0, 4
+  bb.0:
+    successors: %bb.6(0x80000000)
+    liveins: $r0, $r1, $r2
+
+    renamable $r3, dead $cpsr = nuw nsw tADDi3 renamable $r1, 3, 14 /* CC::al */, $noreg
+    renamable $q0 = MVE_VDUP32 killed renamable $r1, 0, $noreg, undef renamable $q0
+    renamable $r3 = t2ANDri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $lr = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
+    renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
+    renamable $lr = nuw nsw t2ADDrs killed renamable $r3, killed renamable $lr, 19, 14 /* CC::al */, $noreg, $noreg
+    $lr = t2DoLoopStart renamable $lr
+
+  bb.6 (align 4):
+    successors: %bb.6(0x7c000000), %bb.8(0x04000000)
+    liveins: $lr, $q0, $r0, $r1, $r2, $q2
+
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    renamable $vpr = MVE_VCTP32 renamable $r1, 0, $noreg
+    renamable $r1, dead $cpsr = tSUBi8 killed renamable $r1, 4, 14 /* CC::al */, $noreg
+    MVE_VPST 8, implicit $vpr
+    renamable $r0, renamable $q1 = MVE_VLDRWU32_post killed renamable $r0, 16, 1, renamable $vpr
+    MVE_VPST 4, implicit $vpr
+    renamable $vpr = MVE_VCMPf32 renamable $q1, renamable $q0, 12, 1, killed renamable $vpr
+    renamable $q2 = MVE_VORR renamable $q1, renamable $q1, 1, renamable $vpr, killed renamable $q2
+    MVE_VPST 8, implicit $vpr
+    renamable $q1 = MVE_VORR killed renamable $q1, renamable $q0, 1, renamable $vpr, renamable $q1
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.8, 14 /* CC::al */, $noreg
+
+  bb.8:
+    liveins: $r2, $r12, $q0
+    frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+  bb.9 (align 4):
+    CONSTPOOL_ENTRY 0, %const.0, 4
+
+...