diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -5579,16 +5579,23 @@
                         << "\n");
       return;
     }
-    // Bail out if we have a PHI on an EHPad that gets a value from a
-    // CatchSwitchInst.  Because the CatchSwitchInst cannot be split, there is
-    // no good place to stick any instructions.
+
     if (auto *PN = dyn_cast<PHINode>(U.getUser())) {
        auto *FirstNonPHI = PN->getParent()->getFirstNonPHI();
        if (isa<FuncletPadInst>(FirstNonPHI) ||
            isa<CatchSwitchInst>(FirstNonPHI))
+         // Bail out if we have a PHI on an EHPad that gets a value from a
+         // CatchSwitchInst. Because the CatchSwitchInst cannot be split, there
+         // is no good place to stick any instructions.
          for (BasicBlock *PredBB : PN->blocks())
            if (isa<CatchSwitchInst>(PredBB->getFirstNonPHI()))
              return;
+
+       // Also bail out if we have a PHI with a value from a block ending in a
+       // CallBrInst, because those also can't be split for similar reasons.
+       for (BasicBlock *PredBB : PN->blocks())
+         if (isa<CallBrInst>(PredBB->getTerminator()))
+           return;
     }
   }
 
diff --git a/llvm/test/Transforms/LoopStrengthReduce/callbr-critical-edge-splitting.ll b/llvm/test/Transforms/LoopStrengthReduce/callbr-critical-edge-splitting.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/callbr-critical-edge-splitting.ll
@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -loop-reduce | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Test that we don't try to break a critical edge to a block ending in a callbr
+; instruction. See https://github.com/ClangBuiltLinux/linux/issues/1252
+
+define dso_local i32 @test1() local_unnamed_addr {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@test1, [[COND_TRUE_I:%.*]]), i8* blockaddress(@test1, [[FOR_END:%.*]]))
+; CHECK-NEXT:    to label [[ASM_FALLTHROUGH_I_I:%.*]] [label [[COND_TRUE_I]], label %for.end]
+; CHECK:       asm.fallthrough.i.i:
+; CHECK-NEXT:    unreachable
+; CHECK:       cond.true.i:
+; CHECK-NEXT:    br label [[DO_BODY_I_I_DO_BODY_I_I_CRIT_EDGE:%.*]]
+; CHECK:       do.body.i.i.do.body.i.i_crit_edge:
+; CHECK-NEXT:    [[PGOCOUNT711:%.*]] = phi i64 [ [[TMP0:%.*]], [[DO_BODY_I_I_DO_BODY_I_I_CRIT_EDGE]] ], [ 0, [[COND_TRUE_I]] ]
+; CHECK-NEXT:    [[TMP0]] = add nuw nsw i64 [[PGOCOUNT711]], 1
+; CHECK-NEXT:    br i1 true, label [[DO_BODY_I_I_RDRAND_INT_EXIT_I_CRIT_EDGE:%.*]], label [[DO_BODY_I_I_DO_BODY_I_I_CRIT_EDGE]]
+; CHECK:       do.body.i.i.rdrand_int.exit.i_crit_edge:
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[TMP0]], undef
+; CHECK-NEXT:    br i1 true, label [[FOR_END]], label [[FOR_INC:%.*]]
+; CHECK:       for.inc:
+; CHECK-NEXT:    br label [[FOR_COND]]
+; CHECK:       for.end:
+; CHECK-NEXT:    [[PGOCOUNT_PROMOTED24:%.*]] = phi i64 [ undef, [[FOR_COND]] ], [ [[TMP1]], [[DO_BODY_I_I_RDRAND_INT_EXIT_I_CRIT_EDGE]] ]
+; CHECK-NEXT:    ret i32 undef
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@test1, %cond.true.i), i8* blockaddress(@test1, %for.end))
+  to label %asm.fallthrough.i.i [label %cond.true.i, label %for.end]
+
+asm.fallthrough.i.i:                              ; preds = %for.cond
+  unreachable
+
+cond.true.i:                                      ; preds = %for.cond
+  br label %do.body.i.i.do.body.i.i_crit_edge
+
+do.body.i.i.do.body.i.i_crit_edge:                ; preds = %do.body.i.i.do.body.i.i_crit_edge, %cond.true.i
+  %pgocount711 = phi i64 [ %0, %do.body.i.i.do.body.i.i_crit_edge ], [ 0, %cond.true.i ]
+  %0 = add nuw nsw i64 %pgocount711, 1
+  br i1 undef, label %do.body.i.i.rdrand_int.exit.i_crit_edge, label %do.body.i.i.do.body.i.i_crit_edge
+
+do.body.i.i.rdrand_int.exit.i_crit_edge:          ; preds = %do.body.i.i.do.body.i.i_crit_edge
+  %1 = add i64 %0, undef
+  br i1 undef, label %for.end, label %for.inc
+
+for.inc:                                          ; preds = %do.body.i.i.rdrand_int.exit.i_crit_edge
+  br label %for.cond
+
+for.end:                                          ; preds = %do.body.i.i.rdrand_int.exit.i_crit_edge, %for.cond
+  %pgocount.promoted24 = phi i64 [ undef, %for.cond ], [ %1, %do.body.i.i.rdrand_int.exit.i_crit_edge ]
+  ret i32 undef
+}