[llvm] r333493 - [PM/LoopUnswitch] When using the new SimpleLoopUnswitch pass, schedule
Chandler Carruth via llvm-commits
llvm-commits at lists.llvm.org
Tue May 29 19:46:45 PDT 2018
Author: chandlerc
Date: Tue May 29 19:46:45 2018
New Revision: 333493
URL: http://llvm.org/viewvc/llvm-project?rev=333493&view=rev
Log:
[PM/LoopUnswitch] When using the new SimpleLoopUnswitch pass, schedule
loop-cleanup passes at the beginning of the loop pass pipeline, and
re-enqueue loops after even trivial unswitching.
This will allow us to much more consistently avoid simplifying code
while doing trivial unswitching. I've also added a test case that
specifically shows effective iteration using this technique.
I've unconditionally updated the new PM as that is always using the
SimpleLoopUnswitch pass, and I've made the pipeline changes for the old
PM conditional on using this new unswitch pass. I added a bunch of
comments to the loop pass pipeline in the old PM to make it more clear
what is going on when reviewing.
Hopefully this will unblock doing *partial* unswitching instead of just
full unswitching.
Differential Revision: https://reviews.llvm.org/D47408
Added:
llvm/trunk/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll
Modified:
llvm/trunk/lib/Passes/PassBuilder.cpp
llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
llvm/trunk/test/Other/new-pm-defaults.ll
llvm/trunk/test/Other/new-pm-thinlto-defaults.ll
Modified: llvm/trunk/lib/Passes/PassBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Passes/PassBuilder.cpp?rev=333493&r1=333492&r2=333493&view=diff
==============================================================================
--- llvm/trunk/lib/Passes/PassBuilder.cpp (original)
+++ llvm/trunk/lib/Passes/PassBuilder.cpp Tue May 29 19:46:45 2018
@@ -390,13 +390,21 @@ PassBuilder::buildFunctionSimplification
// Add the primary loop simplification pipeline.
// FIXME: Currently this is split into two loop pass pipelines because we run
- // some function passes in between them. These can and should be replaced by
- // loop pass equivalenst but those aren't ready yet. Specifically,
- // `SimplifyCFGPass` and `InstCombinePass` are used. We have
- // `LoopSimplifyCFGPass` which isn't yet powerful enough, and the closest to
- // the other we have is `LoopInstSimplify`.
+ // some function passes in between them. These can and should be removed
+ // and/or replaced by scheduling the loop pass equivalents in the correct
+ // positions. But those equivalent passes aren't powerful enough yet.
+ // Specifically, `SimplifyCFGPass` and `InstCombinePass` are currently still
+ // used. We have `LoopSimplifyCFGPass` which isn't yet powerful enough yet to
+ // fully replace `SimplifyCFGPass`, and the closest to the other we have is
+ // `LoopInstSimplify`.
LoopPassManager LPM1(DebugLogging), LPM2(DebugLogging);
+ // Simplify the loop body. We do this initially to clean up after other loop
+ // passes run, either when iterating on a loop or on inner loops with
+ // implications on the outer loop.
+ LPM1.addPass(LoopInstSimplifyPass());
+ LPM1.addPass(LoopSimplifyCFGPass());
+
// Rotate Loop - disable header duplication at -Oz
LPM1.addPass(LoopRotatePass(Level != Oz));
LPM1.addPass(LICMPass());
Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=333493&r1=333492&r2=333493&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Tue May 29 19:46:45 2018
@@ -138,10 +138,10 @@ static cl::opt<bool>
cl::Hidden,
cl::desc("Disable shrink-wrap library calls"));
-static cl::opt<bool>
- EnableSimpleLoopUnswitch("enable-simple-loop-unswitch", cl::init(false),
- cl::Hidden,
- cl::desc("Enable the simple loop unswitch pass."));
+static cl::opt<bool> EnableSimpleLoopUnswitch(
+ "enable-simple-loop-unswitch", cl::init(false), cl::Hidden,
+ cl::desc("Enable the simple loop unswitch pass. Also enables independent "
+ "cleanup passes integrated into the loop pass manager pipeline."));
static cl::opt<bool> EnableGVNSink(
"enable-gvn-sink", cl::init(false), cl::Hidden,
@@ -335,6 +335,15 @@ void PassManagerBuilder::addFunctionSimp
MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
MPM.add(createCFGSimplificationPass()); // Merge & remove BBs
MPM.add(createReassociatePass()); // Reassociate expressions
+
+ // Begin the loop pass pipeline.
+ if (EnableSimpleLoopUnswitch) {
+ // The simple loop unswitch pass relies on separate cleanup passes. Schedule
+ // them first so when we re-process a loop they run before other loop
+ // passes.
+ MPM.add(createLoopInstSimplifyPass());
+ MPM.add(createLoopSimplifyCFGPass());
+ }
// Rotate Loop - disable header duplication at -Oz
MPM.add(createLoopRotatePass(SizeLevel == 2 ? 0 : -1));
MPM.add(createLICMPass()); // Hoist loop invariants
@@ -342,20 +351,26 @@ void PassManagerBuilder::addFunctionSimp
MPM.add(createSimpleLoopUnswitchLegacyPass());
else
MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3, DivergentTarget));
+ // FIXME: We break the loop pass pipeline here in order to do full
+ // simplify-cfg. Eventually loop-simplifycfg should be enhanced to replace the
+ // need for this.
MPM.add(createCFGSimplificationPass());
addInstructionCombiningPass(MPM);
+ // We resume loop passes creating a second loop pipeline here.
MPM.add(createIndVarSimplifyPass()); // Canonicalize indvars
MPM.add(createLoopIdiomPass()); // Recognize idioms like memset.
addExtensionsToPM(EP_LateLoopOptimizations, MPM);
MPM.add(createLoopDeletionPass()); // Delete dead loops
if (EnableLoopInterchange) {
+ // FIXME: These are function passes and break the loop pass pipeline.
MPM.add(createLoopInterchangePass()); // Interchange loops
MPM.add(createCFGSimplificationPass());
}
if (!DisableUnrollLoops)
MPM.add(createSimpleLoopUnrollPass(OptLevel)); // Unroll small loops
addExtensionsToPM(EP_LoopOptimizerEnd, MPM);
+ // This ends the loop pass pipelines.
if (OptLevel > 1) {
MPM.add(createMergedLoadStoreMotionPass()); // Merge ld/st in diamonds
Modified: llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp?rev=333493&r1=333492&r2=333493&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp Tue May 29 19:46:45 2018
@@ -1466,7 +1466,7 @@ void visitDomSubTree(DominatorTree &DT,
static bool unswitchInvariantBranch(
Loop &L, BranchInst &BI, DominatorTree &DT, LoopInfo &LI,
AssumptionCache &AC,
- function_ref<void(bool, ArrayRef<Loop *>)> NonTrivialUnswitchCB) {
+ function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB) {
assert(BI.isConditional() && "Can only unswitch a conditional branch!");
assert(L.isLoopInvariant(BI.getCondition()) &&
"Can only unswitch an invariant branch condition!");
@@ -1706,7 +1706,7 @@ static bool unswitchInvariantBranch(
for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops))
if (UpdatedL->getParentLoop() == ParentL)
SibLoops.push_back(UpdatedL);
- NonTrivialUnswitchCB(IsStillLoop, SibLoops);
+ UnswitchCB(IsStillLoop, SibLoops);
++NumBranches;
return true;
@@ -1754,23 +1754,27 @@ computeDomSubtreeCost(DomTreeNode &N,
static bool
unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
TargetTransformInfo &TTI, bool NonTrivial,
- function_ref<void(bool, ArrayRef<Loop *>)> NonTrivialUnswitchCB) {
+ function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB) {
assert(L.isRecursivelyLCSSAForm(DT, LI) &&
"Loops must be in LCSSA form before unswitching.");
- bool Changed = false;
// Must be in loop simplified form: we need a preheader and dedicated exits.
if (!L.isLoopSimplifyForm())
return false;
// Try trivial unswitch first before loop over other basic blocks in the loop.
- Changed |= unswitchAllTrivialConditions(L, DT, LI);
+ if (unswitchAllTrivialConditions(L, DT, LI)) {
+ // If we unswitched successfully we will want to clean up the loop before
+ // processing it further so just mark it as unswitched and return.
+ UnswitchCB(/*CurrentLoopValid*/ true, {});
+ return true;
+ }
// If we're not doing non-trivial unswitching, we're done. We both accept
// a parameter but also check a local flag that can be used for testing
// a debugging.
if (!NonTrivial && !EnableNonTrivialUnswitch)
- return Changed;
+ return false;
// Collect all remaining invariant branch conditions within this loop (as
// opposed to an inner loop which would be handled when visiting that inner
@@ -1785,7 +1789,7 @@ unswitchLoop(Loop &L, DominatorTree &DT,
// If we didn't find any candidates, we're done.
if (UnswitchCandidates.empty())
- return Changed;
+ return false;
// Check if there are irreducible CFG cycles in this loop. If so, we cannot
// easily unswitch non-trivial edges out of the loop. Doing so might turn the
@@ -1796,7 +1800,7 @@ unswitchLoop(Loop &L, DominatorTree &DT,
LoopBlocksRPO RPOT(&L);
RPOT.perform(&LI);
if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI))
- return Changed;
+ return false;
LLVM_DEBUG(
dbgs() << "Considering " << UnswitchCandidates.size()
@@ -1824,10 +1828,10 @@ unswitchLoop(Loop &L, DominatorTree &DT,
continue;
if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
- return Changed;
+ return false;
if (auto CS = CallSite(&I))
if (CS.isConvergent() || CS.cannotDuplicate())
- return Changed;
+ return false;
Cost += TTI.getUserCost(&I);
}
@@ -1898,18 +1902,17 @@ unswitchLoop(Loop &L, DominatorTree &DT,
}
}
- if (BestUnswitchCost < UnswitchThreshold) {
- LLVM_DEBUG(dbgs() << " Trying to unswitch non-trivial (cost = "
- << BestUnswitchCost << ") branch: " << *BestUnswitchTI
- << "\n");
- Changed |= unswitchInvariantBranch(L, cast<BranchInst>(*BestUnswitchTI), DT,
- LI, AC, NonTrivialUnswitchCB);
- } else {
+ if (BestUnswitchCost >= UnswitchThreshold) {
LLVM_DEBUG(dbgs() << "Cannot unswitch, lowest cost found: "
<< BestUnswitchCost << "\n");
+ return false;
}
- return Changed;
+ LLVM_DEBUG(dbgs() << " Trying to unswitch non-trivial (cost = "
+ << BestUnswitchCost << ") branch: " << *BestUnswitchTI
+ << "\n");
+ return unswitchInvariantBranch(L, cast<BranchInst>(*BestUnswitchTI), DT, LI,
+ AC, UnswitchCB);
}
PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,
@@ -1925,10 +1928,11 @@ PreservedAnalyses SimpleLoopUnswitchPass
// after it has been deleted.
std::string LoopName = L.getName();
- auto NonTrivialUnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
- ArrayRef<Loop *> NewLoops) {
+ auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
+ ArrayRef<Loop *> NewLoops) {
// If we did a non-trivial unswitch, we have added new (cloned) loops.
- U.addSiblingLoops(NewLoops);
+ if (!NewLoops.empty())
+ U.addSiblingLoops(NewLoops);
// If the current loop remains valid, we should revisit it to catch any
// other unswitch opportunities. Otherwise, we need to mark it as deleted.
@@ -1939,7 +1943,7 @@ PreservedAnalyses SimpleLoopUnswitchPass
};
if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.TTI, NonTrivial,
- NonTrivialUnswitchCB))
+ UnswitchCB))
return PreservedAnalyses::all();
// Historically this pass has had issues with the dominator tree so verify it
@@ -1987,8 +1991,8 @@ bool SimpleLoopUnswitchLegacyPass::runOn
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
- auto NonTrivialUnswitchCB = [&L, &LPM](bool CurrentLoopValid,
- ArrayRef<Loop *> NewLoops) {
+ auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid,
+ ArrayRef<Loop *> NewLoops) {
// If we did a non-trivial unswitch, we have added new (cloned) loops.
for (auto *NewL : NewLoops)
LPM.addLoop(*NewL);
@@ -2003,7 +2007,7 @@ bool SimpleLoopUnswitchLegacyPass::runOn
};
bool Changed =
- unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, NonTrivialUnswitchCB);
+ unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, UnswitchCB);
// If anything was unswitched, also clear any cached information about this
// loop.
Modified: llvm/trunk/test/Other/new-pm-defaults.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Other/new-pm-defaults.ll?rev=333493&r1=333492&r2=333493&view=diff
==============================================================================
--- llvm/trunk/test/Other/new-pm-defaults.ll (original)
+++ llvm/trunk/test/Other/new-pm-defaults.ll Tue May 29 19:46:45 2018
@@ -145,6 +145,8 @@
; CHECK-O-NEXT: Running analysis: ScalarEvolutionAnalysis
; CHECK-O-NEXT: Running analysis: InnerAnalysisManagerProxy
; CHECK-O-NEXT: Starting Loop pass manager run.
+; CHECK-O-NEXT: Running pass: LoopInstSimplifyPass
+; CHECK-O-NEXT: Running pass: LoopSimplifyCFGPass
; CHECK-O-NEXT: Running pass: LoopRotatePass
; CHECK-O-NEXT: Running pass: LICM
; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
Modified: llvm/trunk/test/Other/new-pm-thinlto-defaults.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Other/new-pm-thinlto-defaults.ll?rev=333493&r1=333492&r2=333493&view=diff
==============================================================================
--- llvm/trunk/test/Other/new-pm-thinlto-defaults.ll (original)
+++ llvm/trunk/test/Other/new-pm-thinlto-defaults.ll Tue May 29 19:46:45 2018
@@ -129,6 +129,8 @@
; CHECK-O-NEXT: Running analysis: ScalarEvolutionAnalysis
; CHECK-O-NEXT: Running analysis: InnerAnalysisManagerProxy
; CHECK-O-NEXT: Starting Loop pass manager run.
+; CHECK-O-NEXT: Running pass: LoopInstSimplifyPass
+; CHECK-O-NEXT: Running pass: LoopSimplifyCFGPass
; CHECK-O-NEXT: Running pass: LoopRotatePass
; CHECK-O-NEXT: Running pass: LICM
; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
Added: llvm/trunk/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll?rev=333493&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll (added)
+++ llvm/trunk/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll Tue May 29 19:46:45 2018
@@ -0,0 +1,41 @@
+; RUN: opt -passes='loop(loop-instsimplify,simplify-cfg,unswitch),verify<loops>' -S < %s | FileCheck %s
+
+declare void @some_func() noreturn
+
+define i32 @test1(i32* %var, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @test1(
+entry:
+ br label %loop_begin
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 %{{.*}}, label %entry.split, label %loop_exit.split
+;
+; CHECK: entry.split:
+; CHECK-NEXT: br i1 %{{.*}}, label %entry.split.split, label %loop_exit
+;
+; CHECK: entry.split.split:
+; CHECK-NEXT: br label %do_something
+
+loop_begin:
+ br i1 %cond1, label %continue, label %loop_exit ; first trivial condition
+
+continue:
+ %var_val = load i32, i32* %var
+ %var_cond = trunc i32 %var_val to i1
+ %maybe_cond = select i1 %cond1, i1 %cond2, i1 %var_cond
+ br i1 %maybe_cond, label %do_something, label %loop_exit ; second trivial condition
+
+do_something:
+ call void @some_func() noreturn nounwind
+ br label %loop_begin
+; CHECK: do_something:
+; CHECK-NEXT: call
+; CHECK-NEXT: br label %do_something
+
+loop_exit:
+ ret i32 0
+; CHECK: loop_exit:
+; CHECK-NEXT: br label %loop_exit.split
+;
+; CHECK: loop_exit.split:
+; CHECK-NEXT: ret
+}
\ No newline at end of file
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