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clang-p2996/llvm/test/CodeGen/Thumb2/LowOverheadLoops/unpredicated-max.mir
David Green 9cb8f4d1ad [ARM] Add a tail-predication loop predicate register 
The semantics of tail predication loops means that the value of LR as an
instruction is executed determines the predicate. In other words:

mov r3, #3
DLSTP lr, r3        // Start tail predication, lr==3
VADD.s32 q0, q1, q2 // Lanes 0,1 and 2 are updated in q0.
mov lr, #1
VADD.s32 q0, q1, q2 // Only first lane is updated.

This means that the value of lr cannot be spilled and re-used in tail
predication regions without potentially altering the behaviour of the
program. More lanes than required could be stored, for example, and in
the case of a gather those lanes might not have been setup, leading to
alignment exceptions.

This patch adds a new lr predicate operand to MVE instructions in order
to keep a reference to the lr that they use as a tail predicate. It will
usually hold the zeroreg meaning not predicated, being set to the LR phi
value in the MVETPAndVPTOptimisationsPass. This will prevent it from
being spilled anywhere that it needs to be used.

A lot of tests needed updating.

Differential Revision: https://reviews.llvm.org/D107638
2021-09-02 13:42:58 +01:00

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# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
# RUN: llc -mtriple=thumbv8.1m.main -mattr=+mve %s -run-pass=arm-low-overhead-loops -o - | FileCheck %s
--- |
define dso_local void @variant_max_use(i16* nocapture readonly %a, i16* %c, i32 %N) #0 {
entry:
%cmp9 = icmp eq i32 %N, 0
%tmp = add i32 %N, 3
%tmp1 = lshr i32 %tmp, 2
%tmp2 = shl nuw i32 %tmp1, 2
%tmp3 = add i32 %tmp2, -4
%tmp4 = lshr i32 %tmp3, 2
%tmp5 = add nuw nsw i32 %tmp4, 1
br i1 %cmp9, label %exit, label %vector.ph
vector.ph: ; preds = %entry
%start = call i32 @llvm.start.loop.iterations.i32(i32 %tmp5)
br label %vector.body
vector.body: ; preds = %vector.body, %vector.ph
%lsr.iv1 = phi i32 [ %lsr.iv.next, %vector.body ], [ %start, %vector.ph ]
%lsr.iv = phi i16* [ %scevgep, %vector.body ], [ %a, %vector.ph ]
%lsr.iv.2 = phi i16* [ %scevgep.2, %vector.body ], [ %c, %vector.ph ]
%tmp7 = phi i32 [ %N, %vector.ph ], [ %tmp9, %vector.body ]
%lsr.iv17 = bitcast i16* %lsr.iv to <8 x i16>*
%tmp8 = call <8 x i1> @llvm.arm.mve.vctp16(i32 %tmp7)
%tmp9 = sub i32 %tmp7, 8
%wide.masked.load = call <8 x i16> @llvm.masked.load.v8i16.p0v8i16(<8 x i16>* %lsr.iv17, i32 2, <8 x i1> %tmp8, <8 x i16> undef)
%min = tail call i16 @llvm.vector.reduce.smax.v8i16(<8 x i16> %wide.masked.load)
store i16 %min, i16* %lsr.iv.2
%scevgep = getelementptr i16, i16* %lsr.iv, i32 8
%scevgep.2 = getelementptr i16, i16* %lsr.iv.2, i32 1
%tmp10 = call i32 @llvm.loop.decrement.reg.i32.i32.i32(i32 %lsr.iv1, i32 1)
%tmp11 = icmp ne i32 %tmp10, 0
%lsr.iv.next = add nsw i32 %lsr.iv1, -1
br i1 %tmp11, label %vector.body, label %exit
exit: ; preds = %vector.body, %entry
ret void
}
declare <8 x i16> @llvm.masked.load.v8i16.p0v8i16(<8 x i16>*, i32 immarg, <8 x i1>, <8 x i16>)
declare i32 @llvm.start.loop.iterations.i32(i32)
declare i32 @llvm.loop.decrement.reg.i32.i32.i32(i32, i32)
declare <8 x i1> @llvm.arm.mve.vctp16(i32)
declare i16 @llvm.vector.reduce.smax.v8i16(<8 x i16>)
...
---
name: variant_max_use
alignment: 2
tracksRegLiveness: true
registers: []
liveins:
- { reg: '$r0', virtual-reg: '' }
- { reg: '$r1', virtual-reg: '' }
- { reg: '$r2', virtual-reg: '' }
frameInfo:
stackSize: 8
offsetAdjustment: 0
maxAlignment: 4
fixedStack: []
stack:
- { id: 0, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
stack-id: default, callee-saved-register: '$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: '$r5', callee-saved-restored: true,
debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
callSites: []
constants: []
machineFunctionInfo: {}
body: |
; CHECK-LABEL: name: variant_max_use
; CHECK: bb.0.entry:
; CHECK: successors: %bb.1(0x80000000)
; CHECK: liveins: $lr, $r0, $r1, $r2, $r5
; CHECK: frame-setup tPUSH 14 /* CC::al */, $noreg, killed $r5, killed $lr, implicit-def $sp, implicit $sp
; CHECK: frame-setup CFI_INSTRUCTION def_cfa_offset 8
; CHECK: frame-setup CFI_INSTRUCTION offset $lr, -4
; CHECK: frame-setup CFI_INSTRUCTION offset $r5, -8
; CHECK: tCMPi8 renamable $r2, 0, 14 /* CC::al */, $noreg, implicit-def $cpsr
; CHECK: t2IT 0, 8, implicit-def $itstate
; CHECK: tPOP_RET 0 /* CC::eq */, killed $cpsr, def $r5, def $pc, implicit killed $itstate
; CHECK: bb.1.vector.ph:
; CHECK: successors: %bb.2(0x80000000)
; CHECK: liveins: $r0, $r1, $r2
; CHECK: renamable $r3, dead $cpsr = tADDi3 renamable $r2, 3, 14 /* CC::al */, $noreg
; CHECK: renamable $r3 = t2BICri killed renamable $r3, 3, 14 /* CC::al */, $noreg, $noreg
; CHECK: renamable $r12 = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
; CHECK: renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
; CHECK: renamable $r3 = nuw nsw t2ADDrs killed renamable $r3, killed renamable $r12, 19, 14 /* CC::al */, $noreg, $noreg
; CHECK: $r12 = t2MOVi16 32768, 14 /* CC::al */, $noreg
; CHECK: $r12 = t2MOVTi16 killed $r12, 65535, 14 /* CC::al */, $noreg
; CHECK: dead $lr = t2DLS renamable $r3
; CHECK: $r5 = tMOVr killed $r3, 14 /* CC::al */, $noreg
; CHECK: bb.2.vector.body:
; CHECK: successors: %bb.2(0x7c000000), %bb.3(0x04000000)
; CHECK: liveins: $r0, $r1, $r2, $r5, $r12
; CHECK: $r3 = tMOVr $r12, 14 /* CC::al */, $noreg
; CHECK: renamable $vpr = MVE_VCTP16 renamable $r2, 0, $noreg, $noreg
; CHECK: MVE_VPST 8, implicit $vpr
; CHECK: renamable $r0, renamable $q0 = MVE_VLDRHU16_post killed renamable $r0, 16, 1, killed renamable $vpr, $noreg :: (load (s128) from %ir.lsr.iv17, align 2)
; CHECK: renamable $r3 = MVE_VMAXVs16 killed renamable $r3, killed renamable $q0, 0, $noreg, $noreg
; CHECK: $lr = tMOVr $r5, 14 /* CC::al */, $noreg
; CHECK: early-clobber renamable $r1 = t2STRH_POST killed renamable $r3, killed renamable $r1, 2, 14 /* CC::al */, $noreg :: (store (s16) into %ir.lsr.iv.2)
; CHECK: renamable $r5, dead $cpsr = nsw tSUBi8 killed $r5, 1, 14 /* CC::al */, $noreg
; CHECK: renamable $r2, dead $cpsr = tSUBi8 killed renamable $r2, 8, 14 /* CC::al */, $noreg
; CHECK: dead $lr = t2LEUpdate killed renamable $lr, %bb.2
; CHECK: bb.3.exit:
; CHECK: tPOP_RET 14 /* CC::al */, $noreg, def $r5, def $pc
bb.0.entry:
successors: %bb.1(0x80000000)
liveins: $r0, $r1, $r2, $r5, $lr
frame-setup tPUSH 14 /* CC::al */, $noreg, killed $r5, killed $lr, implicit-def $sp, implicit $sp
frame-setup CFI_INSTRUCTION def_cfa_offset 8
frame-setup CFI_INSTRUCTION offset $lr, -4
frame-setup CFI_INSTRUCTION offset $r5, -8
tCMPi8 renamable $r2, 0, 14 /* CC::al */, $noreg, implicit-def $cpsr
t2IT 0, 8, implicit-def $itstate
tPOP_RET 0 /* CC::eq */, killed $cpsr, def $r5, def $pc, implicit killed $itstate
bb.1.vector.ph:
successors: %bb.2(0x80000000)
liveins: $r0, $r1, $r2, $r5, $lr
renamable $r3, dead $cpsr = tADDi3 renamable $r2, 3, 14 /* CC::al */, $noreg
renamable $r3 = t2BICri killed renamable $r3, 3, 14 /* CC::al */, $noreg, $noreg
renamable $r12 = t2SUBri killed renamable $r3, 4, 14 /* CC::al */, $noreg, $noreg
renamable $r3, dead $cpsr = tMOVi8 1, 14 /* CC::al */, $noreg
renamable $r3 = nuw nsw t2ADDrs killed renamable $r3, killed renamable $r12, 19, 14 /* CC::al */, $noreg, $noreg
$r12 = t2MOVi16 32768, 14 /* CC::al */, $noreg
$r12 = t2MOVTi16 killed $r12, 65535, 14 /* CC::al */, $noreg
$lr = t2DoLoopStart renamable $r3
$r5 = tMOVr killed $r3, 14 /* CC::al */, $noreg
bb.2.vector.body:
successors: %bb.2(0x7c000000), %bb.3(0x04000000)
liveins: $r0, $r1, $r2, $r5, $r12
$r3 = tMOVr $r12, 14 /* CC::al */, $noreg
renamable $vpr = MVE_VCTP16 renamable $r2, 0, $noreg, $noreg
MVE_VPST 8, implicit $vpr
renamable $r0, renamable $q0 = MVE_VLDRHU16_post killed renamable $r0, 16, 1, killed renamable $vpr, $noreg :: (load (s128) from %ir.lsr.iv17, align 2)
renamable $r3 = MVE_VMAXVs16 killed renamable $r3, killed renamable $q0, 0, $noreg, $noreg
$lr = tMOVr $r5, 14 /* CC::al */, $noreg
early-clobber renamable $r1 = t2STRH_POST killed renamable $r3, killed renamable $r1, 2, 14 /* CC::al */, $noreg :: (store (s16) into %ir.lsr.iv.2)
renamable $r5, dead $cpsr = nsw tSUBi8 killed $r5, 1, 14 /* CC::al */, $noreg
renamable $r2, dead $cpsr = tSUBi8 killed renamable $r2, 8, 14 /* CC::al */, $noreg
renamable $lr = t2LoopDec killed renamable $lr, 1
t2LoopEnd killed renamable $lr, %bb.2, implicit-def dead $cpsr
tB %bb.3, 14 /* CC::al */, $noreg
bb.3.exit:
tPOP_RET 14 /* CC::al */, $noreg, def $r5, def $pc
...
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