[PM] Port LoopSimplify to the new PM

[davide]

Summary

This was pretty mechanical, except for how we handle LCSSAPreserve.
Comments welcome.

[chandlerc]

I'd consolidate the APIs for loop simplify into the new header rather than have them split across multiple headers with this.

include/llvm/Transforms/Utils/LoopSimplify.h

50

missing blank line after this...

(I hate this clang-format bug...)

lib/Transforms/Utils/LoopSimplify.cpp

822–823

Er, this seems odd. Missing ! and return?

826–828

I don't think this comment will really age effectively. We're very likely to delete the old code and not update this in any awy.

[davide]

In D21404#459387, @chandlerc wrote:

I'd consolidate the APIs for loop simplify into the new header rather than have them split across multiple headers with this.

Sorry, I completely missed this comment. Which multiple headers are you referring to?

include/llvm/Transforms/Utils/LoopSimplify.h

+//===- LoopSimplify.h - Loop Canonicalization Pass --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs several transformations to transform natural loops into a
+// simpler form, which makes subsequent analyses and transformations simpler and
+// more effective.
+//
+// Loop pre-header insertion guarantees that there is a single, non-critical
+// entry edge from outside of the loop to the loop header.  This simplifies a
+// number of analyses and transformations, such as LICM.
+//
+// Loop exit-block insertion guarantees that all exit blocks from the loop
+// (blocks which are outside of the loop that have predecessors inside of the
+// loop) only have predecessors from inside of the loop (and are thus dominated
+// by the loop header).  This simplifies transformations such as store-sinking
+// that are built into LICM.
+//
+// This pass also guarantees that loops will have exactly one backedge.
+//
+// Indirectbr instructions introduce several complications. If the loop
+// contains or is entered by an indirectbr instruction, it may not be possible
+// to transform the loop and make these guarantees. Client code should check
+// that these conditions are true before relying on them.
+//
+// Note that the simplifycfg pass will clean up blocks which are split out but
+// end up being unnecessary, so usage of this pass should not pessimize
+// generated code.
+//
+// This pass obviously modifies the CFG, but updates loop information and
+// dominator information.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+#define LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+/// This pass is responsible for loop canonicalization.
+class LoopSimplifyPass : public PassInfoMixin<LoopSimplifyPass> {
+public:
+  PreservedAnalyses run(Function &F, AnalysisManager<Function> &AM);
+};
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H

lib/Passes/PassBuilder.cpp

 #include "llvm/Transforms/Scalar/PartiallyInlineLibCalls.h"
 #include "llvm/Transforms/Scalar/Reassociate.h"
 #include "llvm/Transforms/Scalar/SCCP.h"
 #include "llvm/Transforms/Scalar/SROA.h"
 #include "llvm/Transforms/Scalar/SimplifyCFG.h"
 #include "llvm/Transforms/Scalar/Sink.h"
 #include "llvm/Transforms/Scalar/SLPVectorizer.h"
 #include "llvm/Transforms/Utils/LCSSA.h"
+#include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Utils/Mem2Reg.h"
 #include "llvm/Transforms/Utils/MemorySSA.h"
 
 #include <type_traits>
 
 using namespace llvm;
 
 static Regex DefaultAliasRegex("^(default|lto-pre-link|lto)<(O[0123sz])>$");

lib/Passes/PassRegistry.def

 FUNCTION_PASS("early-cse", EarlyCSEPass())
 FUNCTION_PASS("instcombine", InstCombinePass())
 FUNCTION_PASS("invalidate<all>", InvalidateAllAnalysesPass())
 FUNCTION_PASS("no-op-function", NoOpFunctionPass())
 FUNCTION_PASS("loweratomic", LowerAtomicPass())
 FUNCTION_PASS("lower-expect", LowerExpectIntrinsicPass())
 FUNCTION_PASS("guard-widening", GuardWideningPass())
 FUNCTION_PASS("gvn", GVN())
+FUNCTION_PASS("loop-simplify", LoopSimplifyPass())
 FUNCTION_PASS("mem2reg", PromotePass())
 FUNCTION_PASS("memcpyopt", MemCpyOptPass())
 FUNCTION_PASS("mldst-motion", MergedLoadStoreMotionPass())
 FUNCTION_PASS("jump-threading", JumpThreadingPass())
 FUNCTION_PASS("partially-inline-libcalls", PartiallyInlineLibCallsPass())
 FUNCTION_PASS("lcssa", LCSSAPass())
 FUNCTION_PASS("print", PrintFunctionPass(dbgs()))
 FUNCTION_PASS("print<assumptions>", AssumptionPrinterPass(dbgs()))

lib/Transforms/Utils/LoopSimplify.cpp

 // end up being unnecessary, so usage of this pass should not pessimize
 // generated code.
 //
 // This pass obviously modifies the CFG, but updates loop information and
 // dominator information.
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SetOperations.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
if (PreserveLCSSA) {
     bool InLCSSA =
         all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
     assert(InLCSSA && "LCSSA is broken after loop-simplify.");
   }
 #endif
   return Changed;
 }
 
+PreservedAnalyses LoopSimplifyPass::run(Function &F,
+                                        AnalysisManager<Function> &AM) {
+  bool Changed = false;
+  LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);
+  DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
+  ScalarEvolution *SE = AM.getCachedResult<ScalarEvolutionAnalysis>(F);
+  AssumptionCache *AC = &AM.getResult<AssumptionAnalysis>(F);
+
+  // FIXME: This pass should verify that the loops on which it's operating
+  // are in canonical SSA form, and that the pass itself preserves this form.
+  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+    Changed |= simplifyLoop(*I, DT, LI, SE, AC, true /* PreserveLCSSA */);
+
+  if (Changed)
+    PreservedAnalyses::none();
+  PreservedAnalyses PA;
+
+  // The old PM also preserved LCSSAID and BreakCriticalEdgesID.
+  // This makes no sense in the new PM so we omit those from the set
+  // of preserved passes.
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<LoopAnalysis>();
+  PA.preserve<BasicAA>();
+  PA.preserve<GlobalsAA>();
+  PA.preserve<SCEVAA>();
+  PA.preserve<ScalarEvolutionAnalysis>();
+  PA.preserve<DependenceAnalysis>();
+  return PA;
+}
+
 // FIXME: Restore this code when we re-enable verification in verifyAnalysis
 // below.
 #if 0
 static void verifyLoop(Loop *L) {
   // Verify subloops.
   for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
     verifyLoop(*I);
 

test/Transforms/LoopSimplify/basictest.ll

 ; RUN: opt < %s -loop-simplify
+; RUN: opt < %s -passes=loop-simplify
 
 ; This function should get a preheader inserted before BB3, that is jumped
 ; to by BB1 & BB2
 ;
 
 define void @test() {
   br i1 true, label %BB1, label %BB2
 BB1:    ; preds = %0
   br label %BB3
 BB2:    ; preds = %0
   br label %BB3
 BB3:    ; preds = %BB3, %BB2, %BB1
   br label %BB3
 }