[ARM][LowOverheadLoops] Revert non-header LE target

[samparker]

Summary

Revert the hardware loop upon finding a LoopEnd that doesn't target the loop header, instead of asserting a failure.

[SjoerdMeijer]

lib/Target/ARM/ARMInstrThumb2.td

5224 ↗

(On Diff #211698)

thought this was fixed in D65275, anyway, doesn't matter.

test/CodeGen/Thumb2/LowOverheadLoops/revert-non-header.mir

7 ↗

(On Diff #211698)

It doesn't look like a minimal example to me. Can the test case be easily reduced?

[samparker]

test/CodeGen/Thumb2/LowOverheadLoops/revert-non-header.mir

7 ↗

(On Diff #211698)

yeah, i will give it a go.

[samparker]

Reduced test case and removed change from previous commit.

[dmgreen]

LGTM

llvm/trunk/lib/Target/ARM/ARMLowOverheadLoops.cpp

bool ARMLowOverheadLoops::ProcessLoop(MachineLoop *ML) {
   if (!Start && !Dec && !End) {
     LLVM_DEBUG(dbgs() << "ARM Loops: Not a low-overhead loop.\n");
     return Changed;
   } else if (!(Start && Dec && End)) {
     LLVM_DEBUG(dbgs() << "ARM Loops: Failed to find all loop components.\n");
     return false;
   }
 
-  if (!End->getOperand(1).isMBB() ||
-      End->getOperand(1).getMBB() != ML->getHeader())
-    report_fatal_error("Expected LoopEnd to target Loop Header");
+  if (!End->getOperand(1).isMBB())
+    report_fatal_error("Expected LoopEnd to target basic block");
+
+  // TODO Maybe there's cases where the target doesn't have to be the header,
+  // but for now be safe and revert.
+  if (End->getOperand(1).getMBB() != ML->getHeader()) {
+    LLVM_DEBUG(dbgs() << "ARM Loops: LoopEnd is not targetting header.\n");
+    Revert = true;
+  }
 
   // The WLS and LE instructions have 12-bits for the label offset. WLS
   // requires a positive offset, while LE uses negative.
   if (BBUtils->getOffsetOf(End) < BBUtils->getOffsetOf(ML->getHeader()) ||
       !BBUtils->isBBInRange(End, ML->getHeader(), 4094)) {
     LLVM_DEBUG(dbgs() << "ARM Loops: LE offset is out-of-range\n");
     Revert = true;
   }

llvm/trunk/test/CodeGen/Thumb2/LowOverheadLoops/revert-non-header.mir

+# RUN: llc -mtriple=thumbv8.1m.main -run-pass=arm-low-overhead-loops %s -o - | FileCheck %s
+# CHECK-NOT: t2DLS
+# CHECK: bb.5.for.inc16:
+# CHECK:   $lr = t2SUBri killed renamable $lr, 1, 14
+# CHECK:   t2CMPri $lr, 0, 14
+# CHECK:   t2Bcc %bb.6, 1
+# CHECK:   tB %bb.2
+# CHECK: bb.6.for.cond4.preheader:
+
+--- |
+  define void @header_not_target_unrolled_loop(i32* nocapture %v, i32 %n) {
+  entry:
+    %cmp56 = icmp sgt i32 %n, 1
+    br i1 %cmp56, label %for.cond1.preheader.preheader, label %for.end20
+  
+  for.cond1.preheader.preheader:                    ; preds = %entry
+    br label %for.cond1.preheader
+  
+  for.cond.loopexit:                                ; preds = %for.inc16, %for.cond1.preheader
+    %cmp = icmp sgt i32 %gap.057.in, 3
+    br i1 %cmp, label %for.cond1.preheader, label %for.end20
+  
+  for.cond1.preheader:                              ; preds = %for.cond1.preheader.preheader, %for.cond.loopexit
+    %gap.057.in = phi i32 [ %gap.057, %for.cond.loopexit ], [ %n, %for.cond1.preheader.preheader ]
+    %gap.057 = sdiv i32 %gap.057.in, 2
+    %cmp252 = icmp slt i32 %gap.057, %n
+    %tmp = sub i32 %n, %gap.057
+    call void @llvm.set.loop.iterations.i32(i32 %tmp)
+    br i1 %cmp252, label %for.cond4.preheader.preheader, label %for.cond.loopexit
+  
+  for.cond4.preheader.preheader:                    ; preds = %for.cond1.preheader
+    %tmp2 = mul i32 %gap.057, -4
+    %tmp6 = mul i32 %gap.057, -2
+    %scevgep1 = getelementptr i32, i32* %v, i32 %gap.057
+    %0 = shl i32 %gap.057, 2
+    br label %for.cond4.preheader
+  
+  for.cond4.preheader:                              ; preds = %for.inc16, %for.cond4.preheader.preheader
+    %lsr.iv2 = phi i32* [ %scevgep3, %for.inc16 ], [ %scevgep1, %for.cond4.preheader.preheader ]
+    %lsr.iv = phi i32* [ %v, %for.cond4.preheader.preheader ], [ %scevgep, %for.inc16 ]
+    %i.053 = phi i32 [ %inc, %for.inc16 ], [ %gap.057, %for.cond4.preheader.preheader ]
+    %tmp8 = phi i32 [ %tmp, %for.cond4.preheader.preheader ], [ %tmp16, %for.inc16 ]
+    %j.048 = sub nsw i32 %i.053, %gap.057
+    %cmp549 = icmp sgt i32 %j.048, -1
+    br i1 %cmp549, label %land.rhs.preheader, label %for.inc16
+  
+  land.rhs.preheader:                               ; preds = %for.cond4.preheader
+    br label %land.rhs
+  
+  land.rhs:                                         ; preds = %land.rhs.preheader, %for.body8
+    %lsr.iv4 = phi i32 [ 0, %land.rhs.preheader ], [ %lsr.iv.next, %for.body8 ]
+    %j.051 = phi i32 [ %j.0, %for.body8 ], [ %j.048, %land.rhs.preheader ]
+    %1 = bitcast i32* %lsr.iv2 to i8*
+    %2 = bitcast i32* %lsr.iv to i8*
+    %uglygep10 = getelementptr i8, i8* %2, i32 %lsr.iv4
+    %uglygep1011 = bitcast i8* %uglygep10 to i32*
+    %tmp9 = load i32, i32* %uglygep1011, align 4
+    %uglygep7 = getelementptr i8, i8* %1, i32 %lsr.iv4
+    %uglygep78 = bitcast i8* %uglygep7 to i32*
+    %tmp12 = load i32, i32* %uglygep78, align 4
+    %cmp7 = icmp sgt i32 %tmp9, %tmp12
+    br i1 %cmp7, label %for.body8, label %for.inc16
+  
+  for.body8:                                        ; preds = %land.rhs
+    %3 = bitcast i32* %lsr.iv2 to i8*
+    %4 = bitcast i32* %lsr.iv to i8*
+    %sunkaddr = getelementptr i8, i8* %4, i32 %lsr.iv4
+    %5 = bitcast i8* %sunkaddr to i32*
+    store i32 %tmp12, i32* %5, align 4
+    %uglygep = getelementptr i8, i8* %3, i32 %lsr.iv4
+    %uglygep6 = bitcast i8* %uglygep to i32*
+    store i32 %tmp9, i32* %uglygep6, align 4
+    %j.0 = sub nsw i32 %j.051, %gap.057
+    %lsr.iv.next = add i32 %lsr.iv4, %0
+    %cmp5 = icmp sgt i32 %j.0, -1
+    br i1 %cmp5, label %land.rhs, label %for.inc16
+  
+  for.inc16:                                        ; preds = %for.body8, %land.rhs, %for.cond4.preheader
+    %inc = add nsw i32 %i.053, 1
+    %scevgep = getelementptr i32, i32* %lsr.iv, i32 1
+    %tmp16 = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 %tmp8, i32 1)
+    %tmp17 = icmp ne i32 %tmp16, 0
+    %scevgep3 = getelementptr i32, i32* %lsr.iv2, i32 1
+    br i1 %tmp17, label %for.cond4.preheader, label %for.cond.loopexit
+  
+  for.end20:                                        ; preds = %for.cond.loopexit, %entry
+    ret void
+  }
+  
+  ; Function Attrs: noduplicate nounwind
+  declare void @llvm.set.loop.iterations.i32(i32) #0
+  
+  ; Function Attrs: noduplicate nounwind
+  declare i32 @llvm.loop.decrement.reg.i32.i32.i32(i32, i32) #0
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #1
+  
+  attributes #0 = { noduplicate nounwind }
+  attributes #1 = { nounwind }
+
+...
+---
+name:            header_not_target_unrolled_loop
+alignment:       1
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: false
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$r0', virtual-reg: '' }
+  - { reg: '$r1', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       32
+  offsetAdjustment: 0
+  maxAlignment:    4
+  adjustsStack:    false
+  hasCalls:        false
+  stackProtector:  ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$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: '$r10', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 2, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r9', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 3, name: '', type: spill-slot, offset: -16, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r8', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 4, name: '', type: spill-slot, offset: -20, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 5, name: '', type: spill-slot, offset: -24, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r6', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 6, name: '', type: spill-slot, offset: -28, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r5', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 7, name: '', type: spill-slot, offset: -32, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '$r4', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    successors: %bb.1(0x40000000), %bb.9(0x40000000)
+  
+    $sp = frame-setup t2STMDB_UPD $sp, 14, $noreg, killed $r4, killed $r5, killed $r6, killed $r7, killed $r8, killed $r9, killed $r10, killed $lr
+    frame-setup CFI_INSTRUCTION def_cfa_offset 32
+    frame-setup CFI_INSTRUCTION offset $lr, -4
+    frame-setup CFI_INSTRUCTION offset $r10, -8
+    frame-setup CFI_INSTRUCTION offset $r9, -12
+    frame-setup CFI_INSTRUCTION offset $r8, -16
+    frame-setup CFI_INSTRUCTION offset $r7, -20
+    frame-setup CFI_INSTRUCTION offset $r6, -24
+    frame-setup CFI_INSTRUCTION offset $r5, -28
+    frame-setup CFI_INSTRUCTION offset $r4, -32
+    tCMPi8 renamable $r1, 2, 14, $noreg, implicit-def $cpsr
+    tBcc %bb.9, 11, killed $cpsr
+  
+  bb.1:
+    successors: %bb.3(0x80000000)
+  
+    $r9 = tMOVr $r1, 14, $noreg
+    tB %bb.3, 14, $noreg
+  
+  bb.2.for.cond.loopexit:
+    successors: %bb.3(0x7c000000), %bb.9(0x04000000)
+  
+    t2CMPri killed renamable $r12, 4, 14, $noreg, implicit-def $cpsr
+    tBcc %bb.9, 11, killed $cpsr
+  
+  bb.3.for.cond1.preheader:
+    successors: %bb.4(0x40000000), %bb.2(0x40000000)
+  
+    renamable $r2 = t2ADDrs $r9, $r9, 251, 14, $noreg, $noreg
+    $r12 = tMOVr killed $r9, 14, $noreg
+    renamable $lr = t2SUBrs renamable $r1, renamable $r2, 9, 14, $noreg, $noreg
+    renamable $r9 = t2ASRri renamable $r2, 1, 14, $noreg, $noreg
+    t2CMPrs renamable $r1, killed renamable $r2, 9, 14, $noreg, implicit-def $cpsr
+    t2DoLoopStart renamable $lr
+    tBcc %bb.2, 13, killed $cpsr
+  
+  bb.4.for.cond4.preheader.preheader:
+    successors: %bb.7(0x50000000), %bb.5(0x30000000)
+  
+    renamable $r3 = t2ADDrs renamable $r0, renamable $r9, 18, 14, $noreg, $noreg
+    renamable $r10 = t2LSLri renamable $r9, 2, 14, $noreg, $noreg
+    $r5 = tMOVr $r0, 14, $noreg
+    $r8 = tMOVr $r9, 14, $noreg
+    renamable $r7 = nsw t2SUBrr renamable $r8, renamable $r9, 14, $noreg, def $cpsr
+    tBcc %bb.7, 5, killed $cpsr
+  
+  bb.5.for.inc16:
+    successors: %bb.6(0x7c000000), %bb.2(0x04000000)
+  
+    renamable $r3, dead $cpsr = tADDi8 killed renamable $r3, 4, 14, $noreg
+    renamable $r5, dead $cpsr = tADDi8 killed renamable $r5, 4, 14, $noreg
+    renamable $r8 = nsw t2ADDri killed renamable $r8, 1, 14, $noreg, $noreg
+    renamable $lr = t2LoopDec killed renamable $lr, 1
+    t2LoopEnd renamable $lr, %bb.6, implicit-def dead $cpsr
+    tB %bb.2, 14, $noreg
+  
+  bb.6.for.cond4.preheader:
+    successors: %bb.7(0x50000000), %bb.5(0x30000000)
+  
+    renamable $r7 = nsw t2SUBrr renamable $r8, renamable $r9, 14, $noreg, def $cpsr
+    tBcc %bb.5, 4, killed $cpsr
+  
+  bb.7.land.rhs.preheader:
+    successors: %bb.8(0x80000000)
+  
+    renamable $r6, dead $cpsr = tMOVi8 0, 14, $noreg
+  
+  bb.8.land.rhs:
+    successors: %bb.5(0x07e00000), %bb.8(0x78200000)
+  
+    renamable $r4 = tLDRr renamable $r3, $r6, 14, $noreg :: (load 4 from %ir.uglygep78)
+    renamable $r2 = tLDRr renamable $r5, $r6, 14, $noreg :: (load 4 from %ir.uglygep1011)
+    tCMPr renamable $r2, renamable $r4, 14, $noreg, implicit-def $cpsr
+    t2IT 12, 1, implicit-def $itstate
+    tSTRr killed renamable $r4, renamable $r5, $r6, 12, $cpsr, implicit $itstate :: (store 4 into %ir.5)
+    tSTRr killed renamable $r2, renamable $r3, $r6, 12, $cpsr, implicit $itstate :: (store 4 into %ir.uglygep6)
+    renamable $r6 = tADDhirr killed renamable $r6, renamable $r10, 12, $cpsr, implicit $r6, implicit $itstate
+    renamable $r7 = nsw t2SUBrr killed renamable $r7, renamable $r9, 12, $cpsr, $noreg, implicit $r7, implicit killed $itstate
+    t2IT 12, 8, implicit-def $itstate
+    t2CMPri renamable $r7, -1, 12, killed $cpsr, implicit-def $cpsr, implicit killed $itstate
+    tBcc %bb.8, 12, killed $cpsr
+    tB %bb.5, 14, $noreg
+  
+  bb.9.for.end20:
+    $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $r5, def $r6, def $r7, def $r8, def $r9, def $r10, def $pc
+
+...