diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 4b0f7f38fcc9..00a309972a52 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -58,6 +58,13 @@ static cl::opt<unsigned> AlignAllBlock("align-all-blocks",
                                                 "blocks in the function."),
                                        cl::init(0), cl::Hidden);
 
+// FIXME: Find a good default for this flag and remove the flag.
+static cl::opt<unsigned>
+ExitBlockBias("block-placement-exit-block-bias",
+              cl::desc("Block frequency percentage a loop exit block needs "
+                       "over the original exit to be considered the new exit."),
+              cl::init(0), cl::Hidden);
+
 namespace {
 class BlockChain;
 /// \brief Type for our function-wide basic block -> block chain mapping.
@@ -691,13 +698,15 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F,
       DEBUG(dbgs() << "    exiting: " << getBlockName(*I) << " -> "
                    << getBlockName(*SI) << " [L:" << SuccLoopDepth
                    << "] (" << ExitEdgeFreq << ")\n");
-      // Note that we slightly bias this toward an existing layout successor to
-      // retain incoming order in the absence of better information.
-      // FIXME: Should we bias this more strongly? It's pretty weak.
+      // Note that we bias this toward an existing layout successor to retain
+      // incoming order in the absence of better information. The exit must have
+      // a frequency higher than the current exit before we consider breaking
+      // the layout.
+      BranchProbability Bias(100 - ExitBlockBias, 100);
       if (!ExitingBB || BestExitLoopDepth < SuccLoopDepth ||
           ExitEdgeFreq > BestExitEdgeFreq ||
           ((*I)->isLayoutSuccessor(*SI) &&
-           !(ExitEdgeFreq < BestExitEdgeFreq))) {
+           !(ExitEdgeFreq < BestExitEdgeFreq * Bias))) {
         BestExitEdgeFreq = ExitEdgeFreq;
         ExitingBB = *I;
       }
diff --git a/llvm/test/CodeGen/X86/zlib-longest-match.ll b/llvm/test/CodeGen/X86/zlib-longest-match.ll
new file mode 100644
index 000000000000..d1598dce02d7
--- /dev/null
+++ b/llvm/test/CodeGen/X86/zlib-longest-match.ll
@@ -0,0 +1,240 @@
+; RUN: llc -march=x86-64 < %s -block-placement-exit-block-bias=20 | FileCheck %s
+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-S128"
+target triple = "x86_64-apple-macosx10.9.0"
+
+; This is longest_match, the hot function from zlib's deflate implementation.
+
+%struct.internal_state = type { %struct.z_stream_s*, i32, i8*, i64, i8*, i32, i32, %struct.gz_header_s*, i32, i8, i32, i32, i32, i32, i8*, i64, i16*, i16*, i32, i32, i32, i32, i32, i64, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, [573 x %struct.ct_data_s], [61 x %struct.ct_data_s], [39 x %struct.ct_data_s], %struct.tree_desc_s, %struct.tree_desc_s, %struct.tree_desc_s, [16 x i16], [573 x i32], i32, i32, [573 x i8], i8*, i32, i32, i16*, i64, i64, i32, i32, i16, i32, i64 }
+%struct.z_stream_s = type { i8*, i32, i64, i8*, i32, i64, i8*, %struct.internal_state*, i8* (i8*, i32, i32)*, void (i8*, i8*)*, i8*, i32, i64, i64 }
+%struct.gz_header_s = type { i32, i64, i32, i32, i8*, i32, i32, i8*, i32, i8*, i32, i32, i32 }
+%struct.ct_data_s = type { %union.anon, %union.anon.0 }
+%union.anon = type { i16 }
+%union.anon.0 = type { i16 }
+%struct.tree_desc_s = type { %struct.ct_data_s*, i32, %struct.static_tree_desc_s* }
+%struct.static_tree_desc_s = type { i32 }
+
+; CHECK-LABEL: longest_match:
+
+; Verify that there are no spills or reloads in the loop exit block. This loop
+; is mostly cold, only %do.cond125 and %land.rhs131 are hot.
+; CHECK: %do.cond125
+; CHECK-NOT: {{Spill|Reload}}
+; CHECK: jbe
+
+; Verify that block placement doesn't destroy source order. It's important that
+; the two hot blocks are laid out close to each other.
+; CHECK-NEXT: %land.rhs131
+; CHECK: jne
+; CHECK: jmp
+define i32 @longest_match(%struct.internal_state* nocapture %s, i32 %cur_match) nounwind {
+entry:
+  %max_chain_length = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 31
+  %0 = load i32* %max_chain_length, align 4
+  %window = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 14
+  %1 = load i8** %window, align 8
+  %strstart = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 27
+  %2 = load i32* %strstart, align 4
+  %idx.ext = zext i32 %2 to i64
+  %add.ptr = getelementptr inbounds i8* %1, i64 %idx.ext
+  %prev_length = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 30
+  %3 = load i32* %prev_length, align 4
+  %nice_match1 = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 36
+  %4 = load i32* %nice_match1, align 4
+  %w_size = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 11
+  %5 = load i32* %w_size, align 4
+  %sub = add i32 %5, -262
+  %cmp = icmp ugt i32 %2, %sub
+  %sub6 = sub i32 %2, %sub
+  %sub6. = select i1 %cmp, i32 %sub6, i32 0
+  %prev7 = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 16
+  %6 = load i16** %prev7, align 8
+  %w_mask = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 13
+  %7 = load i32* %w_mask, align 4
+  %add.ptr11.sum = add i64 %idx.ext, 258
+  %add.ptr12 = getelementptr inbounds i8* %1, i64 %add.ptr11.sum
+  %sub13 = add nsw i32 %3, -1
+  %idxprom = sext i32 %sub13 to i64
+  %add.ptr.sum = add i64 %idxprom, %idx.ext
+  %arrayidx = getelementptr inbounds i8* %1, i64 %add.ptr.sum
+  %8 = load i8* %arrayidx, align 1
+  %idxprom14 = sext i32 %3 to i64
+  %add.ptr.sum213 = add i64 %idxprom14, %idx.ext
+  %arrayidx15 = getelementptr inbounds i8* %1, i64 %add.ptr.sum213
+  %9 = load i8* %arrayidx15, align 1
+  %good_match = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 35
+  %10 = load i32* %good_match, align 4
+  %cmp17 = icmp ult i32 %3, %10
+  %shr = lshr i32 %0, 2
+  %chain_length.0 = select i1 %cmp17, i32 %0, i32 %shr
+  %lookahead = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 29
+  %11 = load i32* %lookahead, align 4
+  %cmp18 = icmp ugt i32 %4, %11
+  %. = select i1 %cmp18, i32 %11, i32 %4
+  %match_start = getelementptr inbounds %struct.internal_state* %s, i64 0, i32 28
+  %add.ptr.sum217 = add i64 %idx.ext, 1
+  %arrayidx44 = getelementptr inbounds i8* %1, i64 %add.ptr.sum217
+  %add.ptr.sum218 = add i64 %idx.ext, 2
+  %add.ptr50 = getelementptr inbounds i8* %1, i64 %add.ptr.sum218
+  %sub.ptr.lhs.cast = ptrtoint i8* %add.ptr12 to i64
+  br label %do.body
+
+do.body:                                          ; preds = %land.rhs131, %entry
+  %best_len.0 = phi i32 [ %best_len.1, %land.rhs131 ], [ %3, %entry ]
+  %chain_length.1 = phi i32 [ %dec, %land.rhs131 ], [ %chain_length.0, %entry ]
+  %cur_match.addr.0 = phi i32 [ %conv128, %land.rhs131 ], [ %cur_match, %entry ]
+  %scan_end1.0 = phi i8 [ %scan_end1.1, %land.rhs131 ], [ %8, %entry ]
+  %scan_end.0 = phi i8 [ %scan_end.1, %land.rhs131 ], [ %9, %entry ]
+  %idx.ext23 = zext i32 %cur_match.addr.0 to i64
+  %add.ptr24 = getelementptr inbounds i8* %1, i64 %idx.ext23
+  %idxprom25 = sext i32 %best_len.0 to i64
+  %add.ptr24.sum = add i64 %idx.ext23, %idxprom25
+  %arrayidx26 = getelementptr inbounds i8* %1, i64 %add.ptr24.sum
+  %12 = load i8* %arrayidx26, align 1
+  %cmp28 = icmp eq i8 %12, %scan_end.0
+  br i1 %cmp28, label %lor.lhs.false, label %do.cond125
+
+lor.lhs.false:                                    ; preds = %do.body
+  %sub30 = add nsw i32 %best_len.0, -1
+  %idxprom31 = sext i32 %sub30 to i64
+  %add.ptr24.sum214 = add i64 %idx.ext23, %idxprom31
+  %arrayidx32 = getelementptr inbounds i8* %1, i64 %add.ptr24.sum214
+  %13 = load i8* %arrayidx32, align 1
+  %cmp35 = icmp eq i8 %13, %scan_end1.0
+  br i1 %cmp35, label %lor.lhs.false37, label %do.cond125
+
+lor.lhs.false37:                                  ; preds = %lor.lhs.false
+  %14 = load i8* %add.ptr24, align 1
+  %15 = load i8* %add.ptr, align 1
+  %cmp40 = icmp eq i8 %14, %15
+  br i1 %cmp40, label %lor.lhs.false42, label %do.cond125
+
+lor.lhs.false42:                                  ; preds = %lor.lhs.false37
+  %add.ptr24.sum215 = add i64 %idx.ext23, 1
+  %incdec.ptr = getelementptr inbounds i8* %1, i64 %add.ptr24.sum215
+  %16 = load i8* %incdec.ptr, align 1
+  %17 = load i8* %arrayidx44, align 1
+  %cmp46 = icmp eq i8 %16, %17
+  br i1 %cmp46, label %if.end49, label %do.cond125
+
+if.end49:                                         ; preds = %lor.lhs.false42
+  %incdec.ptr.sum = add i64 %idx.ext23, 2
+  %incdec.ptr51 = getelementptr inbounds i8* %1, i64 %incdec.ptr.sum
+  br label %do.cond
+
+do.cond:                                          ; preds = %land.lhs.true100, %if.end49
+  %match.0 = phi i8* [ %incdec.ptr51, %if.end49 ], [ %incdec.ptr103, %land.lhs.true100 ]
+  %scan.1 = phi i8* [ %add.ptr50, %if.end49 ], [ %incdec.ptr101, %land.lhs.true100 ]
+  %incdec.ptr53 = getelementptr inbounds i8* %scan.1, i64 1
+  %18 = load i8* %incdec.ptr53, align 1
+  %incdec.ptr55 = getelementptr inbounds i8* %match.0, i64 1
+  %19 = load i8* %incdec.ptr55, align 1
+  %cmp57 = icmp eq i8 %18, %19
+  br i1 %cmp57, label %land.lhs.true, label %do.end
+
+land.lhs.true:                                    ; preds = %do.cond
+  %incdec.ptr59 = getelementptr inbounds i8* %scan.1, i64 2
+  %20 = load i8* %incdec.ptr59, align 1
+  %incdec.ptr61 = getelementptr inbounds i8* %match.0, i64 2
+  %21 = load i8* %incdec.ptr61, align 1
+  %cmp63 = icmp eq i8 %20, %21
+  br i1 %cmp63, label %land.lhs.true65, label %do.end
+
+land.lhs.true65:                                  ; preds = %land.lhs.true
+  %incdec.ptr66 = getelementptr inbounds i8* %scan.1, i64 3
+  %22 = load i8* %incdec.ptr66, align 1
+  %incdec.ptr68 = getelementptr inbounds i8* %match.0, i64 3
+  %23 = load i8* %incdec.ptr68, align 1
+  %cmp70 = icmp eq i8 %22, %23
+  br i1 %cmp70, label %land.lhs.true72, label %do.end
+
+land.lhs.true72:                                  ; preds = %land.lhs.true65
+  %incdec.ptr73 = getelementptr inbounds i8* %scan.1, i64 4
+  %24 = load i8* %incdec.ptr73, align 1
+  %incdec.ptr75 = getelementptr inbounds i8* %match.0, i64 4
+  %25 = load i8* %incdec.ptr75, align 1
+  %cmp77 = icmp eq i8 %24, %25
+  br i1 %cmp77, label %land.lhs.true79, label %do.end
+
+land.lhs.true79:                                  ; preds = %land.lhs.true72
+  %incdec.ptr80 = getelementptr inbounds i8* %scan.1, i64 5
+  %26 = load i8* %incdec.ptr80, align 1
+  %incdec.ptr82 = getelementptr inbounds i8* %match.0, i64 5
+  %27 = load i8* %incdec.ptr82, align 1
+  %cmp84 = icmp eq i8 %26, %27
+  br i1 %cmp84, label %land.lhs.true86, label %do.end
+
+land.lhs.true86:                                  ; preds = %land.lhs.true79
+  %incdec.ptr87 = getelementptr inbounds i8* %scan.1, i64 6
+  %28 = load i8* %incdec.ptr87, align 1
+  %incdec.ptr89 = getelementptr inbounds i8* %match.0, i64 6
+  %29 = load i8* %incdec.ptr89, align 1
+  %cmp91 = icmp eq i8 %28, %29
+  br i1 %cmp91, label %land.lhs.true93, label %do.end
+
+land.lhs.true93:                                  ; preds = %land.lhs.true86
+  %incdec.ptr94 = getelementptr inbounds i8* %scan.1, i64 7
+  %30 = load i8* %incdec.ptr94, align 1
+  %incdec.ptr96 = getelementptr inbounds i8* %match.0, i64 7
+  %31 = load i8* %incdec.ptr96, align 1
+  %cmp98 = icmp eq i8 %30, %31
+  br i1 %cmp98, label %land.lhs.true100, label %do.end
+
+land.lhs.true100:                                 ; preds = %land.lhs.true93
+  %incdec.ptr101 = getelementptr inbounds i8* %scan.1, i64 8
+  %32 = load i8* %incdec.ptr101, align 1
+  %incdec.ptr103 = getelementptr inbounds i8* %match.0, i64 8
+  %33 = load i8* %incdec.ptr103, align 1
+  %cmp105 = icmp eq i8 %32, %33
+  %cmp107 = icmp ult i8* %incdec.ptr101, %add.ptr12
+  %or.cond = and i1 %cmp105, %cmp107
+  br i1 %or.cond, label %do.cond, label %do.end
+
+do.end:                                           ; preds = %land.lhs.true100, %land.lhs.true93, %land.lhs.true86, %land.lhs.true79, %land.lhs.true72, %land.lhs.true65, %land.lhs.true, %do.cond
+  %scan.2 = phi i8* [ %incdec.ptr101, %land.lhs.true100 ], [ %incdec.ptr94, %land.lhs.true93 ], [ %incdec.ptr87, %land.lhs.true86 ], [ %incdec.ptr80, %land.lhs.true79 ], [ %incdec.ptr73, %land.lhs.true72 ], [ %incdec.ptr66, %land.lhs.true65 ], [ %incdec.ptr59, %land.lhs.true ], [ %incdec.ptr53, %do.cond ]
+  %sub.ptr.rhs.cast = ptrtoint i8* %scan.2 to i64
+  %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+  %conv109 = trunc i64 %sub.ptr.sub to i32
+  %sub110 = sub nsw i32 258, %conv109
+  %cmp112 = icmp sgt i32 %sub110, %best_len.0
+  br i1 %cmp112, label %if.then114, label %do.cond125
+
+if.then114:                                       ; preds = %do.end
+  store i32 %cur_match.addr.0, i32* %match_start, align 4
+  %cmp115 = icmp slt i32 %sub110, %.
+  br i1 %cmp115, label %if.end118, label %do.end135
+
+if.end118:                                        ; preds = %if.then114
+  %sub119 = add nsw i32 %sub110, -1
+  %idxprom120 = sext i32 %sub119 to i64
+  %add.ptr111.sum = add i64 %idxprom120, %idx.ext
+  %arrayidx121 = getelementptr inbounds i8* %1, i64 %add.ptr111.sum
+  %34 = load i8* %arrayidx121, align 1
+  %idxprom122 = sext i32 %sub110 to i64
+  %add.ptr111.sum216 = add i64 %idxprom122, %idx.ext
+  %arrayidx123 = getelementptr inbounds i8* %1, i64 %add.ptr111.sum216
+  %35 = load i8* %arrayidx123, align 1
+  br label %do.cond125
+
+do.cond125:                                       ; preds = %if.end118, %do.end, %lor.lhs.false42, %lor.lhs.false37, %lor.lhs.false, %do.body
+  %best_len.1 = phi i32 [ %best_len.0, %do.body ], [ %best_len.0, %lor.lhs.false ], [ %best_len.0, %lor.lhs.false37 ], [ %best_len.0, %lor.lhs.false42 ], [ %sub110, %if.end118 ], [ %best_len.0, %do.end ]
+  %scan_end1.1 = phi i8 [ %scan_end1.0, %do.body ], [ %scan_end1.0, %lor.lhs.false ], [ %scan_end1.0, %lor.lhs.false37 ], [ %scan_end1.0, %lor.lhs.false42 ], [ %34, %if.end118 ], [ %scan_end1.0, %do.end ]
+  %scan_end.1 = phi i8 [ %scan_end.0, %do.body ], [ %scan_end.0, %lor.lhs.false ], [ %scan_end.0, %lor.lhs.false37 ], [ %scan_end.0, %lor.lhs.false42 ], [ %35, %if.end118 ], [ %scan_end.0, %do.end ]
+  %and = and i32 %cur_match.addr.0, %7
+  %idxprom126 = zext i32 %and to i64
+  %arrayidx127 = getelementptr inbounds i16* %6, i64 %idxprom126
+  %36 = load i16* %arrayidx127, align 2
+  %conv128 = zext i16 %36 to i32
+  %cmp129 = icmp ugt i32 %conv128, %sub6.
+  br i1 %cmp129, label %land.rhs131, label %do.end135
+
+land.rhs131:                                      ; preds = %do.cond125
+  %dec = add i32 %chain_length.1, -1
+  %cmp132 = icmp eq i32 %dec, 0
+  br i1 %cmp132, label %do.end135, label %do.body
+
+do.end135:                                        ; preds = %land.rhs131, %do.cond125, %if.then114
+  %best_len.2 = phi i32 [ %best_len.1, %land.rhs131 ], [ %best_len.1, %do.cond125 ], [ %sub110, %if.then114 ]
+  %cmp137 = icmp ugt i32 %best_len.2, %11
+  %.best_len.2 = select i1 %cmp137, i32 %11, i32 %best_len.2
+  ret i32 %.best_len.2
+}