[llvm-commits] [llvm] r146578 - in /llvm/trunk: lib/Transforms/Scalar/LoopUnswitch.cpp test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll
Stepan Dyatkovskiy
stpworld at narod.ru
Thu Dec 22 12:31:36 PST 2011
Hi, Chad. I found the problem. The execution time depends on
-loop-unswitch-threshold opt param. It is magic param that controls
loop-unswitch optimization. Now it is 50 by default. 350 optimal for
this test.
A few words about loop-unswitch optimization. Optimizer looking for loop
invariant variables and moves it out of loop. E.g.:
for (...) {
if (A) // A is not changed in loop.
do_A();
else
do_else();
}
Optimizer replaces this loop with two loops: loop when A is true and
with loop when A is false:
if (A) {
for (...)
do_A();
} else {
for (...)
do_else();
}
If loop-unswitch-threshold is small, we ignore most of these cases and
compile time is small. If this param in "middle" we unswitch something:
some branches moved out of loop, but some ones stays in loop and cloned
in new loops, and we scan it two or more times. I hope I submit
optimized patch soon.
The next information helps me a lot. Is it possible to pass opt params
through the clang?
What about all another tests? Was they regressed too?
Thanks.
-Stepan.
Stepan Dyatkovskiy wrote:
> OK. Thanks, Chad. Now I have a time and I look at it.
>
> -Stepan.
>
> Chad Rosier wrote:
>> Hi Stepan,
>> I noticed this patch caused an ~8% compile-time regression for MultiSource/Benchmarks/Prolangs-C++/shapes/shapes for ARMv7 -O3 -mthumb. If you have a moment would you mind taking a look? The test-suite can be downloaded from the llvm repository (See: http://llvm.org/docs/TestingGuide.html#testsuite). Here are the command line arguments I used to reproduce the regression:
>>
>> /Users/mcrosier/llvm-clean/Release+Asserts/Release+Asserts/bin/clang++ -I/Users/mcrosier/llvm-clean/Release+Asserts/projects/test-suite/MultiSource/Benchmarks/Prolangs-C++/shapes -I/Users/mcrosier/llvm-clean/llvm/projects/test-suite/MultiSource/Benchmarks/Prolangs-C++/shapes -I/Users/mcrosier/llvm-clean/Release+Asserts/projects/test-suite/../../../llvm/projects/test-suite/include -I../../../../include -I/Users/mcrosier/llvm-clean/Release+Asserts/include -I/Users/mcrosier/llvm-clean/llvm/include -D_GNU_SOURCE -D__STDC_LIMIT_MACROS -DNDEBUG -DSMALL_PROBLEM_SIZE -O3 -mthumb -miphoneos-version-min=4.0 -Wl,--no-demangle -ccc-install-dir /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin -arch armv7 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.0.Internal.sdk -c /Users/mcrosier/llvm-clean/llvm/projects/test-suite/MultiSource/Benchmarks/Prolangs-C++/shapes/bjarne.cpp -o Output/bjarne.llvm.o
>>
>> Chad
>>
>> For Apple's record this is being tracked by<rdar://problem/10601498>.
>>
>> On Dec 14, 2011, at 11:19 AM, Stepan Dyatkovskiy wrote:
>>
>>> Author: dyatkovskiy
>>> Date: Wed Dec 14 13:19:17 2011
>>> New Revision: 146578
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=146578&view=rev
>>> Log:
>>> Fix for bug #11429: Wrong behaviour for switches. Small improvement for code size heuristics.
>>>
>>> Added:
>>> llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll
>>> llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll
>>> llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll
>>> Modified:
>>> llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
>>>
>>> Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp?rev=146578&r1=146577&r2=146578&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp Wed Dec 14 13:19:17 2011
>>> @@ -71,7 +71,9 @@
>>> // LoopProcessWorklist - Used to check if second loop needs processing
>>> // after RewriteLoopBodyWithConditionConstant rewrites first loop.
>>> std::vector<Loop*> LoopProcessWorklist;
>>> - SmallPtrSet<Value *,8> UnswitchedVals;
>>> +
>>> + // FIXME: Consider custom class for this.
>>> + std::map<const SwitchInst*, SmallPtrSet<const Value *,8> > UnswitchedVals;
>>>
>>> bool OptimizeForSize;
>>> bool redoLoop;
>>> @@ -117,7 +119,15 @@
>>> private:
>>>
>>> virtual void releaseMemory() {
>>> - UnswitchedVals.clear();
>>> + // We need to forget about all switches in the current loop.
>>> + // FIXME: Do it better than enumerating all blocks of code
>>> + // and see if it is a switch instruction.
>>> + for (Loop::block_iterator I = currentLoop->block_begin(),
>>> + E = currentLoop->block_end(); I != E; ++I) {
>>> + SwitchInst* SI = dyn_cast<SwitchInst>((*I)->getTerminator());
>>> + if (SI)
>>> + UnswitchedVals.erase(SI);
>>> + }
>>> }
>>>
>>> /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
>>> @@ -128,6 +138,12 @@
>>> if (I != LoopProcessWorklist.end())
>>> LoopProcessWorklist.erase(I);
>>> }
>>> +
>>> + /// For new loop switches we clone info about values that was
>>> + /// already unswitched and has redundant successors.
>>> + /// Note, that new loop data is stored inside the VMap.
>>> + void CloneUnswitchedVals(const ValueToValueMapTy& VMap,
>>> + const BasicBlock* SrcBB);
>>>
>>> void initLoopData() {
>>> loopHeader = currentLoop->getHeader();
>>> @@ -255,13 +271,25 @@
>>> } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
>>> Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
>>> currentLoop, Changed);
>>> - if (LoopCond&& SI->getNumCases()> 1) {
>>> + unsigned NumCases = SI->getNumCases();
>>> + if (LoopCond&& NumCases> 1) {
>>> // Find a value to unswitch on:
>>> // FIXME: this should chose the most expensive case!
>>> // FIXME: scan for a case with a non-critical edge?
>>> - Constant *UnswitchVal = SI->getCaseValue(1);
>>> + Constant *UnswitchVal = NULL;
>>> +
>>> // Do not process same value again and again.
>>> - if (!UnswitchedVals.insert(UnswitchVal))
>>> + // At this point we have some cases already unswitched and
>>> + // some not yet unswitched. Let's find the first not yet unswitched one.
>>> + for (unsigned i = 1; i< NumCases; ++i) {
>>> + Constant* UnswitchValCandidate = SI->getCaseValue(i);
>>> + if (!UnswitchedVals[SI].count(UnswitchValCandidate)) {
>>> + UnswitchVal = UnswitchValCandidate;
>>> + break;
>>> + }
>>> + }
>>> +
>>> + if (!UnswitchVal)
>>> continue;
>>>
>>> if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
>>> @@ -287,6 +315,23 @@
>>> return Changed;
>>> }
>>>
>>> +/// For new loop switches we clone info about values that was
>>> +/// already unswitched and has redundant successors.
>>> +/// Not that new loop data is stored inside the VMap.
>>> +void LoopUnswitch::CloneUnswitchedVals(const ValueToValueMapTy& VMap,
>>> + const BasicBlock* SrcBB) {
>>> +
>>> + const SwitchInst* SI = dyn_cast<SwitchInst>(SrcBB->getTerminator());
>>> + if (SI&& UnswitchedVals.count(SI)) {
>>> + // Don't clone a totally simplified switch.
>>> + if (isa<Constant>(SI->getCondition()))
>>> + return;
>>> + Value* I = VMap.lookup(SI);
>>> + assert(I&& "All instructions that are in SrcBB must be in VMap.");
>>> + UnswitchedVals[cast<SwitchInst>(I)] = UnswitchedVals[SI];
>>> + }
>>> +}
>>> +
>>> /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
>>> /// loop with no side effects (including infinite loops).
>>> ///
>>> @@ -378,14 +423,25 @@
>>> // Check to see if a successor of the switch is guaranteed to go to the
>>> // latch block or exit through a one exit block without having any
>>> // side-effects. If so, determine the value of Cond that causes it to do
>>> - // this. Note that we can't trivially unswitch on the default case.
>>> - for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
>>> - if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
>>> + // this.
>>> + // Note that we can't trivially unswitch on the default case or
>>> + // on already unswitched cases.
>>> + for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
>>> + BasicBlock* LoopExitCandidate;
>>> + if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
>>> SI->getSuccessor(i)))) {
>>> // Okay, we found a trivial case, remember the value that is trivial.
>>> - if (Val) *Val = SI->getCaseValue(i);
>>> + ConstantInt* CaseVal = SI->getCaseValue(i);
>>> +
>>> + // Check that it was not unswitched before, since already unswitched
>>> + // trivial vals are looks trivial too.
>>> + if (UnswitchedVals[SI].count(CaseVal))
>>> + continue;
>>> + LoopExitBB = LoopExitCandidate;
>>> + if (Val) *Val = CaseVal;
>>> break;
>>> }
>>> + }
>>> }
>>>
>>> // If we didn't find a single unique LoopExit block, or if the loop exit block
>>> @@ -447,8 +503,14 @@
>>> // expansion, and the number of basic blocks, to avoid loops with
>>> // large numbers of branches which cause loop unswitching to go crazy.
>>> // This is a very ad-hoc heuristic.
>>> - if (Metrics.NumInsts> Threshold ||
>>> - Metrics.NumBlocks * 5> Threshold ||
>>> +
>>> + unsigned NumUnswitched =
>>> + (NumSwitches + NumBranches) + 1 /*take in account current iteration*/;
>>> +
>>> + unsigned NumInsts = Metrics.NumInsts * NumUnswitched;
>>> + unsigned NumBlocks = Metrics.NumBlocks * NumUnswitched;
>>> +
>>> + if (NumInsts> Threshold || NumBlocks * 5> Threshold ||
>>> Metrics.containsIndirectBr || Metrics.isRecursive) {
>>> DEBUG(dbgs()<< "NOT unswitching loop %"
>>> << currentLoop->getHeader()->getName()<< ", cost too high:"
>>> @@ -620,6 +682,12 @@
>>> ValueToValueMapTy VMap;
>>> for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
>>> BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
>>> +
>>> + // Inherit simplified switches info for NewBB
>>> + // We needn't pass NewBB since its instructions are already contained
>>> + // inside the VMap.
>>> + CloneUnswitchedVals(VMap, LoopBlocks[i]);
>>> +
>>> NewBlocks.push_back(NewBB);
>>> VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
>>> LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
>>> @@ -945,6 +1013,9 @@
>>> BasicBlock *Switch = SI->getParent();
>>> BasicBlock *SISucc = SI->getSuccessor(DeadCase);
>>> BasicBlock *Latch = L->getLoopLatch();
>>> +
>>> + UnswitchedVals[SI].insert(Val);
>>> +
>>> if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
>>> // If the DeadCase successor dominates the loop latch, then the
>>> // transformation isn't safe since it will delete the sole predecessor edge
>>>
>>> Added: llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll?rev=146578&view=auto
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll (added)
>>> +++ llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll Wed Dec 14 13:19:17 2011
>>> @@ -0,0 +1,91 @@
>>> +; RUN: opt -loop-unswitch -disable-output -stats -info-output-file -< %s | FileCheck --check-prefix=STATS %s
>>> +; RUN: opt -S -loop-unswitch -verify-loop-info -verify-dom-info %s | FileCheck %s
>>> +
>>> +; STATS: 1 loop-simplify - Number of pre-header or exit blocks inserted
>>> +; STATS: 2 loop-unswitch - Number of switches unswitched
>>> +
>>> +; CHECK: %1 = icmp eq i32 %c, 1
>>> +; CHECK-NEXT: br i1 %1, label %.split.us, label %..split_crit_edge
>>> +
>>> +; CHECK: ..split_crit_edge: ; preds = %0
>>> +; CHECK-NEXT: br label %.split
>>> +
>>> +; CHECK: .split.us: ; preds = %0
>>> +; CHECK-NEXT: br label %loop_begin.us
>>> +
>>> +; CHECK: loop_begin.us: ; preds = %loop_begin.backedge.us, %.split.us
>>> +; CHECK-NEXT: %var_val.us = load i32* %var
>>> +; CHECK-NEXT: switch i32 1, label %default.us-lcssa.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us
>>> +
>>> +; CHECK: inc.us: ; preds = %loop_begin.us
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us
>>> +
>>> +; CHECK: .split: ; preds = %..split_crit_edge
>>> +; CHECK-NEXT: %2 = icmp eq i32 %c, 2
>>> +; CHECK-NEXT: br i1 %2, label %.split.split.us, label %.split..split.split_crit_edge
>>> +
>>> +; CHECK: .split..split.split_crit_edge: ; preds = %.split
>>> +; CHECK-NEXT: br label %.split.split
>>> +
>>> +; CHECK: .split.split.us: ; preds = %.split
>>> +; CHECK-NEXT: br label %loop_begin.us1
>>> +
>>> +; CHECK: loop_begin.us1: ; preds = %loop_begin.backedge.us5, %.split.split.us
>>> +; CHECK-NEXT: %var_val.us2 = load i32* %var
>>> +; CHECK-NEXT: switch i32 2, label %default.us-lcssa.us-lcssa.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us3
>>> +; CHECK-NEXT: i32 2, label %dec.us4
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: dec.us4: ; preds = %loop_begin.us1
>>> +; CHECK-NEXT: call void @decf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us5
>>> +
>>> +; CHECK: .split.split: ; preds = %.split..split.split_crit_edge
>>> +; CHECK-NEXT: br label %loop_begin
>>> +
>>> +; CHECK: loop_begin: ; preds = %loop_begin.backedge, %.split.split
>>> +; CHECK-NEXT: %var_val = load i32* %var
>>> +; CHECK-NEXT: switch i32 %c, label %default.us-lcssa.us-lcssa [
>>> +; CHECK-NEXT: i32 1, label %inc
>>> +; CHECK-NEXT: i32 2, label %dec
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: inc: ; preds = %loop_begin
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable.us-lcssa, label %inc.split
>>> +
>>> +; CHECK: dec: ; preds = %loop_begin
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable6, label %dec.split
>>> +
>>> +define i32 @test(i32* %var) {
>>> + %mem = alloca i32
>>> + store i32 2, i32* %mem
>>> + %c = load i32* %mem
>>> +
>>> + br label %loop_begin
>>> +
>>> +loop_begin:
>>> +
>>> + %var_val = load i32* %var
>>> +
>>> + switch i32 %c, label %default [
>>> + i32 1, label %inc
>>> + i32 2, label %dec
>>> + ]
>>> +
>>> +inc:
>>> + call void @incf() noreturn nounwind
>>> + br label %loop_begin
>>> +dec:
>>> + call void @decf() noreturn nounwind
>>> + br label %loop_begin
>>> +default:
>>> + br label %loop_exit
>>> +loop_exit:
>>> + ret i32 0
>>> +}
>>> +
>>> +declare void @incf() noreturn
>>> +declare void @decf() noreturn
>>>
>>> Added: llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll?rev=146578&view=auto
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll (added)
>>> +++ llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll Wed Dec 14 13:19:17 2011
>>> @@ -0,0 +1,84 @@
>>> +; RUN: opt -loop-unswitch -loop-unswitch-threshold 30 -disable-output -stats -info-output-file -< %s | FileCheck --check-prefix=STATS %s
>>> +; RUN: opt -S -loop-unswitch -loop-unswitch-threshold 30 -verify-loop-info -verify-dom-info %s | FileCheck %s
>>> +
>>> +; STATS: 1 loop-simplify - Number of pre-header or exit blocks inserted
>>> +; STATS: 1 loop-unswitch - Number of switches unswitched
>>> +
>>> +; ModuleID = '../llvm/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll'
>>> +
>>> +; CHECK: %1 = icmp eq i32 %c, 1
>>> +; CHECK-NEXT: br i1 %1, label %.split.us, label %..split_crit_edge
>>> +
>>> +; CHECK: ..split_crit_edge: ; preds = %0
>>> +; CHECK-NEXT: br label %.split
>>> +
>>> +; CHECK: .split.us: ; preds = %0
>>> +; CHECK-NEXT: br label %loop_begin.us
>>> +
>>> +; CHECK: loop_begin.us: ; preds = %loop_begin.backedge.us, %.split.us
>>> +; CHECK: switch i32 1, label %second_switch.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us
>>> +
>>> +; CHECK: inc.us: ; preds = %second_switch.us, %loop_begin.us
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us
>>> +
>>> +; CHECK: second_switch.us: ; preds = %loop_begin.us
>>> +; CHECK-NEXT: switch i32 %d, label %default.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: .split: ; preds = %..split_crit_edge
>>> +; CHECK-NEXT: br label %loop_begin
>>> +
>>> +; CHECK: loop_begin: ; preds = %loop_begin.backedge, %.split
>>> +; CHECK: switch i32 %c, label %second_switch [
>>> +; CHECK-NEXT: i32 1, label %loop_begin.inc_crit_edge
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: loop_begin.inc_crit_edge: ; preds = %loop_begin
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable, label %inc
>>> +
>>> +; CHECK: second_switch: ; preds = %loop_begin
>>> +; CHECK-NEXT: switch i32 %d, label %default [
>>> +; CHECK-NEXT: i32 1, label %inc
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: inc: ; preds = %loop_begin.inc_crit_edge, %second_switch
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge
>>> +
>>> +define i32 @test(i32* %var) {
>>> + %mem = alloca i32
>>> + store i32 2, i32* %mem
>>> + %c = load i32* %mem
>>> + %d = load i32* %mem
>>> +
>>> + br label %loop_begin
>>> +
>>> +loop_begin:
>>> +
>>> + %var_val = load i32* %var
>>> +
>>> + switch i32 %c, label %second_switch [
>>> + i32 1, label %inc
>>> + ]
>>> +
>>> +second_switch:
>>> + switch i32 %d, label %default [
>>> + i32 1, label %inc
>>> + ]
>>> +
>>> +inc:
>>> + call void @incf() noreturn nounwind
>>> + br label %loop_begin
>>> +
>>> +default:
>>> + br label %loop_begin
>>> +
>>> +loop_exit:
>>> + ret i32 0
>>> +}
>>> +
>>> +declare void @incf() noreturn
>>> +declare void @decf() noreturn
>>>
>>> Added: llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll?rev=146578&view=auto
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll (added)
>>> +++ llvm/trunk/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll Wed Dec 14 13:19:17 2011
>>> @@ -0,0 +1,138 @@
>>> +; RUN: opt -loop-unswitch -loop-unswitch-threshold 1000 -disable-output -stats -info-output-file -< %s | FileCheck --check-prefix=STATS %s
>>> +; RUN: opt -S -loop-unswitch -loop-unswitch-threshold 1000 -verify-loop-info -verify-dom-info %s | FileCheck %s
>>> +
>>> +; STATS: 1 loop-simplify - Number of pre-header or exit blocks inserted
>>> +; STATS: 3 loop-unswitch - Number of switches unswitched
>>> +
>>> +; CHECK: %1 = icmp eq i32 %c, 1
>>> +; CHECK-NEXT: br i1 %1, label %.split.us, label %..split_crit_edge
>>> +
>>> +; CHECK: ..split_crit_edge: ; preds = %0
>>> +; CHECK-NEXT: br label %.split
>>> +
>>> +; CHECK: .split.us: ; preds = %0
>>> +; CHECK-NEXT: %2 = icmp eq i32 %d, 1
>>> +; CHECK-NEXT: br i1 %2, label %.split.us.split.us, label %.split.us..split.us.split_crit_edge
>>> +
>>> +; CHECK: .split.us..split.us.split_crit_edge: ; preds = %.split.us
>>> +; CHECK-NEXT: br label %.split.us.split
>>> +
>>> +; CHECK: .split.us.split.us: ; preds = %.split.us
>>> +; CHECK-NEXT: br label %loop_begin.us.us
>>> +
>>> +; CHECK: loop_begin.us.us: ; preds = %loop_begin.backedge.us.us, %.split.us.split.us
>>> +; CHECK-NEXT: %var_val.us.us = load i32* %var
>>> +; CHECK-NEXT: switch i32 1, label %second_switch.us.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us.us
>>> +
>>> +; CHECK: inc.us.us: ; preds = %second_switch.us.us, %loop_begin.us.us
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us.us
>>> +
>>> +; CHECK: second_switch.us.us: ; preds = %loop_begin.us.us
>>> +; CHECK-NEXT: switch i32 1, label %default.us.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us.us
>>> +
>>> +; CHECK: .split.us.split: ; preds = %.split.us..split.us.split_crit_edge
>>> +; CHECK-NEXT: br label %loop_begin.us
>>> +
>>> +; CHECK: loop_begin.us: ; preds = %loop_begin.backedge.us, %.split.us.split
>>> +; CHECK-NEXT: %var_val.us = load i32* %var
>>> +; CHECK-NEXT: switch i32 1, label %second_switch.us [
>>> +; CHECK-NEXT: i32 1, label %inc.us
>>> +
>>> +; CHECK: inc.us: ; preds = %second_switch.us.inc.us_crit_edge, %loop_begin.us
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us
>>> +
>>> +; CHECK: second_switch.us: ; preds = %loop_begin.us
>>> +; CHECK-NEXT: switch i32 %d, label %default.us [
>>> +; CHECK-NEXT: i32 1, label %second_switch.us.inc.us_crit_edge
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: second_switch.us.inc.us_crit_edge: ; preds = %second_switch.us
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable8, label %inc.us
>>> +
>>> +; CHECK: .split: ; preds = %..split_crit_edge
>>> +; CHECK-NEXT: %3 = icmp eq i32 %d, 1
>>> +; CHECK-NEXT: br i1 %3, label %.split.split.us, label %.split..split.split_crit_edge
>>> +
>>> +; CHECK: .split..split.split_crit_edge: ; preds = %.split
>>> +; CHECK-NEXT: br label %.split.split
>>> +
>>> +; CHECK: .split.split.us: ; preds = %.split
>>> +; CHECK-NEXT: br label %loop_begin.us1
>>> +
>>> +; CHECK: loop_begin.us1: ; preds = %loop_begin.backedge.us6, %.split.split.us
>>> +; CHECK-NEXT: %var_val.us2 = load i32* %var
>>> +; CHECK-NEXT: switch i32 %c, label %second_switch.us4 [
>>> +; CHECK-NEXT: i32 1, label %loop_begin.inc_crit_edge.us
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: inc.us3: ; preds = %loop_begin.inc_crit_edge.us, %second_switch.us4
>>> +; CHECK-NEXT: call void @incf() noreturn nounwind
>>> +; CHECK-NEXT: br label %loop_begin.backedge.us6
>>> +
>>> +; CHECK: second_switch.us4: ; preds = %loop_begin.us1
>>> +; CHECK-NEXT: switch i32 1, label %default.us5 [
>>> +; CHECK-NEXT: i32 1, label %inc.us3
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: loop_begin.inc_crit_edge.us: ; preds = %loop_begin.us1
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable.us-lcssa.us, label %inc.us3
>>> +
>>> +; CHECK: .split.split: ; preds = %.split..split.split_crit_edge
>>> +; CHECK-NEXT: br label %loop_begin
>>> +
>>> +; CHECK: loop_begin: ; preds = %loop_begin.backedge, %.split.split
>>> +; CHECK-NEXT: %var_val = load i32* %var
>>> +; CHECK-NEXT: switch i32 %c, label %second_switch [
>>> +; CHECK-NEXT: i32 1, label %loop_begin.inc_crit_edge
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: loop_begin.inc_crit_edge: ; preds = %loop_begin
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable.us-lcssa, label %inc
>>> +
>>> +; CHECK: second_switch: ; preds = %loop_begin
>>> +; CHECK-NEXT: switch i32 %d, label %default [
>>> +; CHECK-NEXT: i32 1, label %second_switch.inc_crit_edge
>>> +; CHECK-NEXT: ]
>>> +
>>> +; CHECK: second_switch.inc_crit_edge: ; preds = %second_switch
>>> +; CHECK-NEXT: br i1 true, label %us-unreachable7, label %inc
>>> +
>>> +
>>> +define i32 @test(i32* %var) {
>>> + %mem = alloca i32
>>> + store i32 2, i32* %mem
>>> + %c = load i32* %mem
>>> + %d = load i32* %mem
>>> +
>>> + br label %loop_begin
>>> +
>>> +loop_begin:
>>> +
>>> + %var_val = load i32* %var
>>> +
>>> + switch i32 %c, label %second_switch [
>>> + i32 1, label %inc
>>> + ]
>>> +
>>> +second_switch:
>>> + switch i32 %d, label %default [
>>> + i32 1, label %inc
>>> + ]
>>> +
>>> +inc:
>>> + call void @incf() noreturn nounwind
>>> + br label %loop_begin
>>> +
>>> +default:
>>> + br label %loop_begin
>>> +
>>> +loop_exit:
>>> + ret i32 0
>>> +}
>>> +
>>> +declare void @incf() noreturn
>>> +declare void @decf() noreturn
>>>
>>>
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