Fix the LoopUnroller to handle nontrivial loops and partial unrolling.

These are not individual bug fixes. I had to rewrite a good chunk of
the unroller to make it sane. I think it was getting lucky on trivial
completely unrolled loops with no early exits. I included some fairly
simple unit tests for partial unrolling. I didn't do much stress
testing, so it may not be perfect, but should be usable now.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137190 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 227 insertions, 52 deletions

diff --git a/include/llvm/Analysis/LoopInfo.h b/include/llvm/Analysis/LoopInfo.h
index 28a15ed..48c59ac 100644
--- a/include/llvm/Analysis/LoopInfo.h
+++ b/include/llvm/Analysis/LoopInfo.h
@@ -134,6 +134,11 @@ public:
   block_iterator block_begin() const { return Blocks.begin(); }
   block_iterator block_end() const { return Blocks.end(); }
 
+  /// getNumBlocks - Get the number of blocks in this loop.
+  unsigned getNumBlocks() const {
+    return std::distance(block_begin(), block_end());
+  }
+
   /// isLoopExiting - True if terminator in the block can branch to another
   /// block that is outside of the current loop.
   ///
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index fa508d4..f17098f 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -21,6 +21,7 @@
 #include "llvm/BasicBlock.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopIterator.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Support/Debug.h"
@@ -225,11 +226,25 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
   Headers.push_back(Header);
   Latches.push_back(LatchBlock);
 
+  // The current on-the-fly SSA update requires blocks to be processed in
+  // reverse postorder so that LastValueMap contains the correct value at each
+  // exit.
+  LoopBlocksDFS DFS(L);
+  {
+    // Traverse the loop blocks using depth-first search to record RPO numbers
+    // for each block in the DFS result.
+    LoopBlocksTraversal Traversal(DFS, LI);
+    for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
+           POE = Traversal.end(); POI != POE; ++POI);
+  }
+  // Stash the DFS iterators before adding blocks to the loop.
+  LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
+  LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
+
   for (unsigned It = 1; It != Count; ++It) {
     std::vector<BasicBlock*> NewBlocks;
 
-    for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(),
-         E = LoopBlocks.end(); BB != E; ++BB) {
+    for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
       ValueToValueMapTy VMap;
       BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
       Header->getParent()->getBasicBlockList().push_back(New);
@@ -255,35 +270,27 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
 
       L->addBasicBlockToLoop(New, LI->getBase());
 
-      // Add phi entries for newly created values to all exit blocks except
-      // the successor of the latch block.  The successor of the exit block will
-      // be updated specially after unrolling all the way.
-      if (*BB != LatchBlock)
-        for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB); SI != SE;
-             ++SI)
-          if (!L->contains(*SI))
-            for (BasicBlock::iterator BBI = (*SI)->begin();
-                 PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
-              Value *Incoming = phi->getIncomingValueForBlock(*BB);
-              phi->addIncoming(Incoming, New);
-            }
-
+      // Add phi entries for newly created values to all exit blocks.
+      for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB);
+           SI != SE; ++SI) {
+        if (L->contains(*SI))
+          continue;
+        for (BasicBlock::iterator BBI = (*SI)->begin();
+             PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
+          Value *Incoming = phi->getIncomingValueForBlock(*BB);
+          ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
+          if (It != LastValueMap.end())
+            Incoming = It->second;
+          phi->addIncoming(Incoming, New);
+        }
+      }
       // Keep track of new headers and latches as we create them, so that
       // we can insert the proper branches later.
       if (*BB == Header)
         Headers.push_back(New);
-      if (*BB == LatchBlock) {
+      if (*BB == LatchBlock)
         Latches.push_back(New);
 
-        // Also, clear out the new latch's back edge so that it doesn't look
-        // like a new loop, so that it's amenable to being merged with adjacent
-        // blocks later on.
-        TerminatorInst *Term = New->getTerminator();
-        assert(L->contains(Term->getSuccessor(!ContinueOnTrue)));
-        assert(Term->getSuccessor(ContinueOnTrue) == LoopExit);
-        Term->setSuccessor(!ContinueOnTrue, NULL);
-      }
-
       NewBlocks.push_back(New);
     }
 
@@ -294,36 +301,24 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
         ::RemapInstruction(I, LastValueMap);
   }
 
-  // The latch block exits the loop.  If there are any PHI nodes in the
-  // successor blocks, update them to use the appropriate values computed as the
-  // last iteration of the loop.
-  if (Count != 1) {
-    BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]);
-    for (succ_iterator SI = succ_begin(LatchBlock), SE = succ_end(LatchBlock);
-         SI != SE; ++SI) {
-      for (BasicBlock::iterator BBI = (*SI)->begin();
-           PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
-        Value *InVal = PN->removeIncomingValue(LatchBlock, false);
-        // If this value was defined in the loop, take the value defined by the
-        // last iteration of the loop.
-        if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
-          if (L->contains(InValI))
-            InVal = LastValueMap[InVal];
-        }
-        PN->addIncoming(InVal, LastIterationBB);
-      }
-    }
-  }
-
-  // Now, if we're doing complete unrolling, loop over the PHI nodes in the
-  // original block, setting them to their incoming values.
-  if (CompletelyUnroll) {
-    BasicBlock *Preheader = L->getLoopPreheader();
-    for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
-      PHINode *PN = OrigPHINode[i];
+  // Loop over the PHI nodes in the original block, setting incoming values.
+  for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
+    PHINode *PN = OrigPHINode[i];
+    if (CompletelyUnroll) {
       PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
       Header->getInstList().erase(PN);
     }
+    else if (Count > 1) {
+      Value *InVal = PN->removeIncomingValue(LatchBlock, false);
+      // If this value was defined in the loop, take the value defined by the
+      // last iteration of the loop.
+      if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
+        if (L->contains(InValI))
+          InVal = LastValueMap[InVal];
+      }
+      assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
+      PN->addIncoming(InVal, Latches.back());
+    }
   }
 
   // Now that all the basic blocks for the unrolled iterations are in place,
@@ -355,6 +350,19 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
       // iteration.
       Term->setSuccessor(!ContinueOnTrue, Dest);
     } else {
+      // Remove phi operands at this loop exit
+      if (Dest != LoopExit) {
+        BasicBlock *BB = Latches[i];
+        for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
+             SI != SE; ++SI) {
+          if (*SI == Headers[i])
+            continue;
+          for (BasicBlock::iterator BBI = (*SI)->begin();
+               PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
+            Phi->removeIncomingValue(BB, false);
+          }
+        }
+      }
       // Replace the conditional branch with an unconditional one.
       BranchInst::Create(Dest, Term);
       Term->eraseFromParent();
diff --git a/test/Transforms/LoopUnroll/2011-08-08-PhiUpdate.ll b/test/Transforms/LoopUnroll/2011-08-08-PhiUpdate.ll
new file mode 100644
index 0000000..3353e51
--- /dev/null
+++ b/test/Transforms/LoopUnroll/2011-08-08-PhiUpdate.ll
@@ -0,0 +1,100 @@
+; RUN: opt < %s -loop-unroll -S -unroll-count=4 | FileCheck %s
+; Test phi update after partial unroll.
+
+declare i1 @check() nounwind
+
+; CHECK: @test
+; CHECK: if.else:
+; CHECK: if.then.loopexit
+; CHECK: %sub5.lcssa = phi i32 [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ]
+; CHECK: if.else.3
+define void @test1(i32 %i, i32 %j) nounwind uwtable ssp {
+entry:
+  %cond1 = call zeroext i1 @check()
+  br i1 %cond1, label %if.then, label %if.else.lr.ph
+
+if.else.lr.ph:                                    ; preds = %entry
+  br label %if.else
+
+if.else:                                          ; preds = %if.else, %if.else.lr.ph
+  %sub = phi i32 [ %i, %if.else.lr.ph ], [ %sub5, %if.else ]
+  %sub5 = sub i32 %sub, %j
+  %cond2 = call zeroext i1 @check()
+  br i1 %cond2, label %if.then, label %if.else
+
+if.then:                                          ; preds = %if.else, %entry
+  %i.tr = phi i32 [ %i, %entry ], [ %sub5, %if.else ]
+  ret void
+
+}
+
+; PR7318: assertion failure after doing a simple loop unroll
+;
+; CHECK: @test2
+; CHECK: bb1.bb2_crit_edge:
+; CHECK: %.lcssa = phi i32 [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ]
+; CHECK: bb1.3:
+define i32 @test2(i32* nocapture %p, i32 %n) nounwind readonly {
+entry:
+  %0 = icmp sgt i32 %n, 0                         ; <i1> [#uses=1]
+  br i1 %0, label %bb.nph, label %bb2
+
+bb.nph:                                           ; preds = %entry
+  %tmp = zext i32 %n to i64                       ; <i64> [#uses=1]
+  br label %bb
+
+bb:                                               ; preds = %bb.nph, %bb1
+  %indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %bb1 ] ; <i64> [#uses=2]
+  %s.01 = phi i32 [ 0, %bb.nph ], [ %2, %bb1 ]    ; <i32> [#uses=1]
+  %scevgep = getelementptr i32* %p, i64 %indvar   ; <i32*> [#uses=1]
+  %1 = load i32* %scevgep, align 1                ; <i32> [#uses=1]
+  %2 = add nsw i32 %1, %s.01                      ; <i32> [#uses=2]
+  br label %bb1
+
+bb1:                                              ; preds = %bb
+  %indvar.next = add i64 %indvar, 1               ; <i64> [#uses=2]
+  %exitcond = icmp ne i64 %indvar.next, %tmp      ; <i1> [#uses=1]
+  br i1 %exitcond, label %bb, label %bb1.bb2_crit_edge
+
+bb1.bb2_crit_edge:                                ; preds = %bb1
+  %.lcssa = phi i32 [ %2, %bb1 ]                  ; <i32> [#uses=1]
+  br label %bb2
+
+bb2:                                              ; preds = %bb1.bb2_crit_edge, %entry
+  %s.0.lcssa = phi i32 [ %.lcssa, %bb1.bb2_crit_edge ], [ 0, %entry ] ; <i32> [#uses=1]
+  ret i32 %s.0.lcssa
+}
+
+; Check phi update for loop with an early-exit.
+;
+; CHECK: @test3
+; CHECK: return.loopexit:
+; CHECK: %tmp7.i.lcssa = phi i32 [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ]
+; CHECK: exit.3:
+define i32 @test3() nounwind uwtable ssp align 2 {
+entry:
+  br i1 undef, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  br label %do.body
+
+do.body:                                          ; preds = %do.cond, %if.end
+  br i1 undef, label %exit, label %do.cond
+
+exit:                  ; preds = %do.body
+  %tmp7.i = load i32* undef, align 8
+  br i1 undef, label %do.cond, label %land.lhs.true
+
+land.lhs.true:                                    ; preds = %exit
+  br i1 undef, label %return, label %do.cond
+
+do.cond:                                          ; preds = %land.lhs.true, %exit, %do.body
+  br i1 undef, label %do.end, label %do.body
+
+do.end:                                           ; preds = %do.cond
+  br label %return
+
+return:                                           ; preds = %do.end, %land.lhs.true, %entry
+  %retval.0 = phi i32 [ 0, %do.end ], [ 0, %entry ], [ %tmp7.i, %land.lhs.true ]
+  ret i32 %retval.0
+}
diff --git a/test/Transforms/LoopUnroll/2011-08-09-PhiUpdate.ll b/test/Transforms/LoopUnroll/2011-08-09-PhiUpdate.ll
new file mode 100644
index 0000000..c1221f5
--- /dev/null
+++ b/test/Transforms/LoopUnroll/2011-08-09-PhiUpdate.ll
@@ -0,0 +1,62 @@
+; RUN: opt -S < %s -instcombine -inline -jump-threading -loop-unroll -unroll-count=4 | FileCheck %s
+;
+; This is a test case that required a number of setup passes because
+; it depends on block order.
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-macosx10.6.8"
+
+declare i1 @check() nounwind
+declare i32 @getval() nounwind
+
+; Check that the loop exit merges values from all the iterations. This
+; could be a tad fragile, but it's a good test.
+;
+; CHECK: @foo
+; CHECK: return:
+; CHECK: %retval.0 = phi i32 [ %tmp7.i, %land.lhs.true ], [ 0, %do.cond ], [ %tmp7.i.1, %land.lhs.true.1 ], [ 0, %do.cond.1 ], [ %tmp7.i.2, %land.lhs.true.2 ], [ 0, %do.cond.2 ], [ %tmp7.i.3, %land.lhs.true.3 ], [ 0, %do.cond.3 ]
+; CHECK-NOT: @bar
+; CHECK: bar.exit.3
+define i32 @foo() uwtable ssp align 2 {
+entry:
+  br i1 undef, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  %call2 = call i32 @getval()
+  br label %do.body
+
+do.body:                                          ; preds = %do.cond, %if.end
+  %call6 = call i32 @bar()
+  %cmp = icmp ne i32 %call6, 0
+  br i1 %cmp, label %land.lhs.true, label %do.cond
+
+land.lhs.true:                                    ; preds = %do.body
+  %call10 = call i32 @getval()
+  %cmp11 = icmp eq i32 0, %call10
+  br i1 %cmp11, label %return, label %do.cond
+
+do.cond:                                          ; preds = %land.lhs.true, %do.body
+  %cmp18 = icmp sle i32 0, %call2
+  br i1 %cmp18, label %do.body, label %return
+
+return:                                           ; preds = %do.cond, %land.lhs.true, %entry
+  %retval.0 = phi i32 [ 0, %entry ], [ %call6, %land.lhs.true ], [ 0, %do.cond ]
+  ret i32 %retval.0
+}
+
+define linkonce_odr i32 @bar() nounwind uwtable ssp align 2 {
+entry:
+  br i1 undef, label %land.lhs.true, label %cond.end
+
+land.lhs.true:                                    ; preds = %entry
+  %cmp4 = call zeroext i1 @check()
+  br i1 %cmp4, label %cond.true, label %cond.end
+
+cond.true:                                        ; preds = %land.lhs.true
+  %tmp7 = call i32 @getval()
+  br label %cond.end
+
+cond.end:                                         ; preds = %cond.true, %land.lhs.true, %entry
+  %cond = phi i32 [ %tmp7, %cond.true ], [ 0, %land.lhs.true ], [ 0, %entry ]
+  ret i32 %cond
+}