[ARM][LowOverheadLoops] Convert intermediate vpr use assertion to condition

[samtebbs]

Summary

This converts the intermediate VPR use assertion to a condition in the if-statement to protect against assertion failures in case behaviuour is changed.

This is a follow-up to https://reviews.llvm.org/D90935 and implements the post-approval comments.

[dmgreen]

Thanks. LGTM

[samtebbs]

Fix test ordering. This is an NFC so I will commit with the previous approval.

llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp

if (VPTState::isEntryPredicatedOnVCTP(Block, /*exclusive*/ true)) {
       assert(getVPTInstrPredicate(*Next) != ARMVCC::None &&
              "The instruction after a VPST must be predicated");
       (void)Next;
       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())) {
-          // 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(!std::any_of(++MachineBasicBlock::iterator(VCMP),
-                              MachineBasicBlock::iterator(VPST), hasVPRUse) &&
-                 "Instructions between the VCMP and VPST are not expected to "
-                 "be predicated");
+        // the same values at the VPST.
+        // If any of the instructions between the VCMP and VPST are predicated
+        // then a different code path is expected to have merged the VCMP and
+        // VPST already.
+        if (!std::any_of(++MachineBasicBlock::iterator(VCMP),
+            RDA->hasSameReachingDef(VCMP, VPST, VCMP->getOperand(1).getReg()) &&
+            RDA->hasSameReachingDef(VCMP, VPST, VCMP->getOperand(2).getReg())) {
           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

while.end6:
     ret void
   }
 
   define void @combine_last() {
   while.end6:
     ret void
   }
 
+  define void @combine_kill_flags() {
+  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
body:             |
   ; 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:   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)
bb.6 (align 4):
     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
+    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.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_kill_flags
+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_kill_flags
+  ; 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 killed renamable $q2, renamable $q1, 0, $noreg, killed renamable $q2
+  ; CHECK:   MVE_VPTv4f32 8, renamable $q0, killed renamable $q1, 12, implicit-def $vpr
+  ; CHECK:   renamable $q0 = MVE_VORR killed renamable $q0, killed renamable $q0, 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, $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 $vpr = MVE_VCMPf32 renamable $q0, renamable $q1, 12, 1, killed renamable $vpr
+    renamable $q2 = MVE_VORR renamable $q2, killed renamable $q1, 0, $noreg, killed renamable $q2
+    MVE_VPST 8, implicit $vpr
+    renamable $q0 = MVE_VORR renamable $q0, renamable $q0, 1, 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_diff_reg_value
 alignment:       8
 exposesReturnsTwice: false
 legalized:       false
 regBankSelected: false
 selected:        false
 failedISel:      false
 tracksRegLiveness: true