Speculatively revert r146578 to determine if it is the cause of a number of

performance regressions (both execution-time and compile-time) on our
nightly testers.

Original commit message:
Fix for bug #11429: Wrong behaviour for switches. Small improvement for code
size heuristics.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147131 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopUnswitch.cpp

@@ -71,9 +71,7 @@ namespace {
     // 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;
@@ -119,15 +117,7 @@ namespace {
   private:
 
     virtual void releaseMemory() {
-      // We need to forget about all switches in the current loop.
+      UnswitchedVals.clear();
-      // 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,
@@ -138,12 +128,6 @@ namespace {
       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();
@@ -271,25 +255,13 @@ bool LoopUnswitch::processCurrentLoop() {
     } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
       Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), 
                                              currentLoop, Changed);
-      unsigned NumCases = SI->getNumCases(); 
+      if (LoopCond && SI->getNumCases() > 1) {
-      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 = NULL;
+        Constant *UnswitchVal = SI->getCaseValue(1);
-        
         // Do not process same value again and again.
-        // At this point we have some cases already unswitched and
+        if (!UnswitchedVals.insert(UnswitchVal))
-        // 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)) {
@@ -315,23 +287,6 @@ bool LoopUnswitch::processCurrentLoop() {
   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).
 ///
@@ -423,25 +378,14 @@ bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
     // 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. 
+    // this.  Note that we can't trivially unswitch on the default case.
-    // Note that we can't trivially unswitch on the default case or
+    for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
-    // on already unswitched cases.
+      if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, 
-    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.
-        ConstantInt* CaseVal = SI->getCaseValue(i);
+        if (Val) *Val = 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
@@ -503,14 +447,8 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
   // 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 ||
-  unsigned NumUnswitched =
+      Metrics.NumBlocks * 5 > Threshold ||
-      (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: "
@@ -682,12 +620,6 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
   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);
@@ -1013,9 +945,6 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
     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

test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll

@@ -1,91 +0,0 @@
-; 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

test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll

@@ -1,84 +0,0 @@
-; 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

test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll

@@ -1,138 +0,0 @@
-; 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