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

llvm-svn: 146578
2024-11-24 03:33:20 +01:00 · 2011-12-14 19:19:17 +00:00 · 2011-12-14 19:19:17 +00:00 · 14cb78c6fb
commit 14cb78c6fb
parent e9572aa680
4 changed files with 395 additions and 11 deletions
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@ -71,7 +71,9 @@ 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;
@ -117,7 +119,15 @@ namespace {
  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 @@ 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();
@ -255,13 +271,25 @@ bool LoopUnswitch::processCurrentLoop() {
    } 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 @@ 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).
 ///
@ -378,14 +423,25 @@ 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.  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 @@ 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 ||
-      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 @@ 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);
@ -945,6 +1013,9 @@ 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
--- a/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll
+++ b/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll
@ -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
--- a/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll
+++ b/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches-Threshold.ll
@ -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
--- a/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll
+++ b/test/Transforms/LoopUnswitch/2011-11-18-TwoSwitches.ll
@ -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