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[MachineOutliner] Sort by Benefit to Cost Ratio (#90264)
This PR depends on #90260 We changed the order in which functions are outlined in Machine Outliner. The formula for priority is found via a black-box Bayesian optimization toolbox. Using this formula for sorting consistently reduces the uncompressed size of large real-world mobile apps. We also ran a few benchmarks using LLVM test suites, and showed that sorting by priority consistently reduces the text segment size. |run (CTMark/)   |baseline (1)|priority (2)|diff (1 -> 2)| |----------------|------------|------------|-------------| |lencod          |349624      |349264      |-0.1030%     | |SPASS           |219672      |219480      |-0.0874%     | |kc              |271956      |251200      |-7.6321%     | |sqlite3         |223920      |223708      |-0.0947%     | |7zip-benchmark  |405364      |402624      |-0.6759%     | |bullet          |139820      |139500      |-0.2289%     | |consumer-typeset|295684      |290196      |-1.8560%     | |pairlocalalign  |72236       |72092       |-0.1993%     | |tramp3d-v4      |189572      |189292      |-0.1477%     | This is part of an enhanced version of machine outliner -- see [RFC](https://discourse.llvm.org/t/rfc-enhanced-machine-outliner-part-1-fulllto-part-2-thinlto-nolto-to-come/78732).
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lines changed

‎llvm/lib/CodeGen/MachineOutliner.cpp

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -828,10 +828,12 @@ bool MachineOutliner::outline(Module &M,
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<< "\n");
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bool OutlinedSomething = false;
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831-
// Sort by benefit. The most beneficial functions should be outlined first.
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// Sort by priority where priority := getNotOutlinedCost / getOutliningCost.
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// The function with highest priority should be outlined first.
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stable_sort(FunctionList,
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[](const OutlinedFunction &LHS, const OutlinedFunction &RHS) {
834-
return LHS.getBenefit() > RHS.getBenefit();
835+
return LHS.getNotOutlinedCost() * RHS.getOutliningCost() >
836+
RHS.getNotOutlinedCost() * LHS.getOutliningCost();
835837
});
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// Walk over each function, outlining them as we go along. Functions are

‎llvm/test/CodeGen/AArch64/machine-outliner-sort-per-priority.ll

Lines changed: 96 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,96 @@
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; This tests the order in which functions are outlined in MachineOutliner
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; There are TWO key OutlinedFunction in FunctionList
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;
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; ===================== First One =====================
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; ```
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; mov w0, #1
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; mov w1, #2
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; mov w2, #3
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; mov w3, #4
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; mov w4, #5
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; ```
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; It has:
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; - `SequenceSize=20` and `OccurrenceCount=6`
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; - each Candidate has `CallOverhead=12` and `FrameOverhead=4`
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; - `NotOutlinedCost=20*6=120` and `OutliningCost=12*6+20+4=96`
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; - `Benefit=120-96=24` and `Priority=120/96=1.25`
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;
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; ===================== Second One =====================
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; ```
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; mov w6, #6
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; mov w7, #7
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; b
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; ```
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; It has:
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; - `SequenceSize=12` and `OccurrenceCount=4`
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; - each Candidate has `CallOverhead=4` and `FrameOverhead=0`
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; - `NotOutlinedCost=12*4=48` and `OutliningCost=4*4+12+0=28`
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; - `Benefit=48-28=20` and `Priority=48/28=1.71`
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;
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; Note that the first one has higher benefit, but lower priority.
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; Hence, when outlining per priority, the second one will be outlined first.
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; RUN: llc %s -enable-machine-outliner=always -filetype=obj -o %t
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; RUN: llvm-objdump -d %t | FileCheck %s --check-prefix=CHECK-SORT-BY-PRIORITY
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; RUN: llc %s -enable-machine-outliner=always -outliner-benefit-threshold=22 -filetype=obj -o %t
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; RUN: llvm-objdump -d %t | FileCheck %s --check-prefix=CHECK-THRESHOLD
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target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
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target triple = "arm64-apple-macosx14.0.0"
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declare i32 @_Z3fooiiii(i32 noundef, i32 noundef, i32 noundef, i32 noundef, i32 noundef, i32 noundef, i32 noundef, i32 noundef)
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define i32 @_Z2f1v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 11, i32 noundef 6, i32 noundef 7)
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ret i32 %1
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}
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define i32 @_Z2f2v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 12, i32 noundef 6, i32 noundef 7)
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ret i32 %1
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}
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define i32 @_Z2f3v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 13, i32 noundef 6, i32 noundef 7)
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ret i32 %1
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}
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define i32 @_Z2f4v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 14, i32 noundef 6, i32 noundef 7)
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ret i32 %1
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}
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define i32 @_Z2f5v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 15, i32 noundef 8, i32 noundef 9)
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ret i32 %1
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}
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define i32 @_Z2f6v() minsize {
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%1 = tail call i32 @_Z3fooiiii(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, i32 noundef 16, i32 noundef 9, i32 noundef 8)
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ret i32 %1
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}
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; CHECK-SORT-BY-PRIORITY: <_OUTLINED_FUNCTION_0>:
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w6, #0x6
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w7, #0x7
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; CHECK-SORT-BY-PRIORITY-NEXT: b
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; CHECK-SORT-BY-PRIORITY: <_OUTLINED_FUNCTION_1>:
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w0, #0x1
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w1, #0x2
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w2, #0x3
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w3, #0x4
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; CHECK-SORT-BY-PRIORITY-NEXT: mov w4, #0x5
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; CHECK-SORT-BY-PRIORITY-NEXT: ret
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; CHECK-THRESHOLD: <_OUTLINED_FUNCTION_0>:
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; CHECK-THRESHOLD-NEXT: mov w0, #0x1
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; CHECK-THRESHOLD-NEXT: mov w1, #0x2
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; CHECK-THRESHOLD-NEXT: mov w2, #0x3
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; CHECK-THRESHOLD-NEXT: mov w3, #0x4
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; CHECK-THRESHOLD-NEXT: mov w4, #0x5
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; CHECK-THRESHOLD-NEXT: ret
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; CHECK-THRESHOLD-NOT: <_OUTLINED_FUNCTION_1>:

‎llvm/test/CodeGen/AArch64/machine-outliner-sort-per-priority.mir

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# The content of this test is modfied upon the output obtained from running
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# `bin/llc -O2 -stop-before=machine-outliner <path_to_llvm_project>/llvm/test/CodeGen/AArch64/machine-outliner-sort-per-priority.ll -o -`
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# RUN: llc -mtriple=aarch64 -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
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--- |
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declare i32 @foo()
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define void @f1() #0 { ret void }
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define void @f2() #0 { ret void }
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define void @f3() #0 { ret void }
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define void @f4() #0 { ret void }
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define void @f5() #0 { ret void }
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define void @f6() #0 { ret void }
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attributes #0 = { minsize }
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...
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---
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# CHECK-LABEL: name: f1
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
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# CHECK-NEXT: $w5 = MOVZWi 11, 0
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# CHECK-NEXT: TCRETURNdi @OUTLINED_FUNCTION_0
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name: f1
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tracksRegLiveness: true
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frameInfo:
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isCalleeSavedInfoValid: true
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machineFunctionInfo:
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hasRedZone: false
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body: |
34+
bb.0:
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$w0 = MOVZWi 1, 0
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$w1 = MOVZWi 2, 0
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$w2 = MOVZWi 3, 0
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$w3 = MOVZWi 4, 0
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$w4 = MOVZWi 5, 0
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$w5 = MOVZWi 11, 0
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$w6 = MOVZWi 6, 0
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$w7 = MOVZWi 7, 0
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TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
44+
45+
...
46+
---
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# CHECK-LABEL: name: f2
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
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# CHECK-NEXT: $w5 = MOVZWi 12, 0
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# CHECK-NEXT: TCRETURNdi @OUTLINED_FUNCTION_0
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name: f2
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tracksRegLiveness: true
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frameInfo:
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isCalleeSavedInfoValid: true
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machineFunctionInfo:
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hasRedZone: false
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body: |
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bb.0:
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$w0 = MOVZWi 1, 0
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$w1 = MOVZWi 2, 0
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$w2 = MOVZWi 3, 0
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$w3 = MOVZWi 4, 0
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$w4 = MOVZWi 5, 0
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$w5 = MOVZWi 12, 0
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$w6 = MOVZWi 6, 0
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$w7 = MOVZWi 7, 0
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TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
73+
74+
...
75+
---
76+
# CHECK-LABEL: name: f3
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
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# CHECK-NEXT: $w5 = MOVZWi 13, 0
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# CHECK-NEXT: TCRETURNdi @OUTLINED_FUNCTION_0
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name: f3
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tracksRegLiveness: true
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frameInfo:
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isCalleeSavedInfoValid: true
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machineFunctionInfo:
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hasRedZone: false
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body: |
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bb.0:
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$w0 = MOVZWi 1, 0
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$w1 = MOVZWi 2, 0
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$w2 = MOVZWi 3, 0
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$w3 = MOVZWi 4, 0
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$w4 = MOVZWi 5, 0
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$w5 = MOVZWi 13, 0
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$w6 = MOVZWi 6, 0
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$w7 = MOVZWi 7, 0
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TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
102+
103+
...
104+
---
105+
# CHECK-LABEL: name: f4
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
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# CHECK-NEXT: $w5 = MOVZWi 14, 0
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# CHECK-NEXT: TCRETURNdi @OUTLINED_FUNCTION_0
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name: f4
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tracksRegLiveness: true
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frameInfo:
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isCalleeSavedInfoValid: true
118+
machineFunctionInfo:
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hasRedZone: false
120+
body: |
121+
bb.0:
122+
$w0 = MOVZWi 1, 0
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$w1 = MOVZWi 2, 0
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$w2 = MOVZWi 3, 0
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$w3 = MOVZWi 4, 0
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$w4 = MOVZWi 5, 0
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$w5 = MOVZWi 14, 0
128+
$w6 = MOVZWi 6, 0
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$w7 = MOVZWi 7, 0
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TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
131+
132+
...
133+
---
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# CHECK-LABEL: name: f5
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
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# CHECK-NOT: @OUTLINED_FUNCTION_0
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name: f5
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tracksRegLiveness: true
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frameInfo:
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isCalleeSavedInfoValid: true
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machineFunctionInfo:
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hasRedZone: false
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body: |
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bb.0:
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$w0 = MOVZWi 1, 0
151+
$w1 = MOVZWi 2, 0
152+
$w2 = MOVZWi 3, 0
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$w3 = MOVZWi 4, 0
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$w4 = MOVZWi 5, 0
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$w5 = MOVZWi 15, 0
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$w6 = MOVZWi 8, 0
157+
$w7 = MOVZWi 9, 0
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TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
159+
160+
...
161+
---
162+
# CHECK-LABEL: name: f6
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $lr
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# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $x5 = ORRXrs $xzr, $lr, 0
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_1
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# CHECK-NEXT: $lr = ORRXrs $xzr, $x5, 0
169+
# CHECK-NOT: @OUTLINED_FUNCTION_0
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name: f6
171+
tracksRegLiveness: true
172+
frameInfo:
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isCalleeSavedInfoValid: true
174+
machineFunctionInfo:
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hasRedZone: false
176+
body: |
177+
bb.0:
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$w0 = MOVZWi 1, 0
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$w1 = MOVZWi 2, 0
180+
$w2 = MOVZWi 3, 0
181+
$w3 = MOVZWi 4, 0
182+
$w4 = MOVZWi 5, 0
183+
$w5 = MOVZWi 16, 0
184+
$w6 = MOVZWi 9, 0
185+
$w7 = MOVZWi 8, 0
186+
TCRETURNdi @foo, 0, csr_darwin_aarch64_aapcs, implicit $sp, implicit killed $w0, implicit killed $w1, implicit killed $w2, implicit killed $w3, implicit killed $w4, implicit killed $w5, implicit killed $w6, implicit killed $w7
187+
188+
...
189+
190+
# CHECK-LABEL: name: OUTLINED_FUNCTION_0
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# CHECK-LABEL: bb.0:
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# CHECK-NEXT: liveins: $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28, $lr, $d8, $d9, $d10, $d11, $d12, $d13, $d14, $d15, $w0, $w1, $w2, $w3, $w4, $w5
193+
# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $w6 = MOVZWi 6, 0
195+
# CHECK-NEXT: $w7 = MOVZWi 7, 0
196+
197+
# CHECK-LABEL: name: OUTLINED_FUNCTION_1
198+
# CHECK-LABEL: bb.0:
199+
# CHECK-NEXT: liveins: $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28, $lr, $d8, $d9, $d10, $d11, $d12, $d13, $d14, $d15
200+
# CHECK-NEXT: {{ $}}
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# CHECK-NEXT: $w0 = MOVZWi 1, 0
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# CHECK-NEXT: $w1 = MOVZWi 2, 0
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# CHECK-NEXT: $w2 = MOVZWi 3, 0
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# CHECK-NEXT: $w3 = MOVZWi 4, 0
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# CHECK-NEXT: $w4 = MOVZWi 5, 0
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# CHECK-NEXT: RET $lr

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