Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -101,6 +101,10 @@
              "to speculatively execute to fold a 2-entry PHI node into a "
              "select (default = 4)"));
 
+static cl::opt<bool> CheckDomBlockInstructionsCount(
+    "simplifycfg-db-instr-count", cl::Hidden, cl::init(false),
+    cl::desc("Do not merge BBs if domblock already has more than phi-node-folding-threshold instructions"));
+
 static cl::opt<bool> DupRet(
     "simplifycfg-dup-ret", cl::Hidden, cl::init(false),
     cl::desc("Duplicate return instructions into unconditional branches"));
@@ -2413,6 +2417,25 @@
                     << "  T: " << IfTrue->getName()
                     << "  F: " << IfFalse->getName() << "\n");
 
+  // We need to be sure, that DomBlock has
+  // enough room for new instructions
+  // First add cost of Select instruction, that will be added to this block
+  // (this cost is equal to number of phi nodes in BB)
+  unsigned Cost = NumPhis;
+
+  if (CheckDomBlockInstructionsCount) {
+    for (const auto& Instr : *DomBlock)
+    {
+      if (!isa<BranchInst>(&Instr))
+        Cost += TTI.getUserCost(&Instr);
+    }
+
+    if (Cost > PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic) {
+      // DomBlock already too large
+      return false;
+    }
+  }
+
   // If we can still promote the PHI nodes after this gauntlet of tests,
   // do all of the PHI's now.
   Instruction *InsertPt = DomBlock->getTerminator();
Index: llvm/test/Transforms/SimplifyCFG/AArch64/check-instr-cost-for-folding.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/AArch64/check-instr-cost-for-folding.ll
@@ -0,0 +1,47 @@
+; RUN: opt < %s -simplifycfg-db-instr-count=true -mtriple=aarch64-linux-gnu -simplifycfg -S >%t
+; RUN: FileCheck %s < %t
+; ModuleID = 'test_func.c'
+
+%struct.ptr_wrapper = type { i32*, i8* }
+
+@g_wrapper = external dso_local local_unnamed_addr global %struct.ptr_wrapper*, align 8
+
+define dso_local i32 @test_func(i64 %in, i64 %bit, i64 %mask) local_unnamed_addr {
+entry:
+  %cmp16 = icmp eq i64 %bit, 0
+  br i1 %cmp16, label %for.end, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %entry
+; CHECK-LABEL: for.body.lr.ph:
+; CHECK-NOT: select
+  %0 = load %struct.ptr_wrapper*, %struct.ptr_wrapper** @g_wrapper, align 8
+  %proc = getelementptr inbounds %struct.ptr_wrapper, %struct.ptr_wrapper* %0, i64 0, i32 1
+  %and2 = and i64 %mask, 1
+  %tobool3 = icmp eq i64 %and2, 0
+  %and = and i64 %bit, %in
+  %tobool = icmp eq i64 %and, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %for.body.lr.ph
+  %or = or i64 0, %bit
+  %inc = add nsw i32 0, 1
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %for.body.lr.ph
+  %retval1.1 = phi i32 [ %inc, %if.then ], [ 0, %for.body.lr.ph ]
+  %res_in.1 = phi i64 [ %or, %if.then ], [ 0, %for.body.lr.ph ]
+  %1 = xor i1 %tobool, true
+  %2 = xor i1 %tobool3, true
+  %3 = or i1 %1, %2
+  store i8* null, i8** %proc, align 8
+  %shl = shl i64 %bit, 1
+  %cmp = icmp eq i64 %shl, 0
+  br label %for.end
+
+for.end:                                          ; preds = %if.end, %entry
+  %retval1.0.lcssa = phi i32 [ 0, %entry ], [ %retval1.1, %if.end ]
+  %res_in.0.lcssa = phi i64 [ 0, %entry ], [ %res_in.1, %if.end ]
+  %4 = trunc i64 %res_in.0.lcssa to i32
+  %conv7 = add i32 %retval1.0.lcssa, %4
+  ret i32 %conv7
+}