Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -50,6 +50,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/SimplifyIndVar.h"
 using namespace llvm;
 
@@ -2175,10 +2176,17 @@
 
   // Clean up dead instructions.
   Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
+
   // Check a post-condition.
   assert(L->isLCSSAForm(*DT) &&
          "Indvars did not leave the loop in lcssa form!");
 
+  // When expanding add recurrences for loop L, SCEVExpander can break LCSSA for
+  // loops inside it (i.e. L's children).
+  if (Changed)
+    for (Loop *SubLoop : L->getSubLoops())
+      formLCSSARecursively(*SubLoop, *DT, LI, SE);
+
   // Verify that LFTR, and any other change have not interfered with SCEV's
   // ability to compute trip count.
 #ifndef NDEBUG
Index: test/Transforms/IndVarSimplify/pr24804.ll
===================================================================
--- /dev/null
+++ test/Transforms/IndVarSimplify/pr24804.ll
@@ -0,0 +1,25 @@
+; RUN: opt -indvars -loop-idiom -loop-deletion -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Checking for a crash
+
+define void @f(i32* %a) {
+; CHECK-LABEL: @f(
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %for.cond, %entry
+  %0 = phi i32 [ 0, %entry ], [ %add, %for.inc ], [ %0, %for.cond ]
+  %add = add nsw i32 %0, 1
+  %idxprom = sext i32 %add to i64
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
+  br i1 undef, label %for.cond, label %for.inc
+
+for.inc:                                          ; preds = %for.cond
+  br i1 undef, label %for.cond, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  ret void
+}
Index: test/Transforms/IndVarSimplify/pr25578.ll
===================================================================
--- /dev/null
+++ test/Transforms/IndVarSimplify/pr25578.ll
@@ -0,0 +1,47 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; CHECK-LABEL: @foo
+define void @foo() {
+entry:
+  br label %L1_header
+
+L1_header:
+  br label %L2_header
+
+; CHECK: L2_header:
+; CHECK: %[[INDVAR:.*]] = phi i64
+L2_header:
+  %i = phi i32 [ 0, %L1_header ], [ %i_next, %L2_latch ]
+  %i_prom = sext i32 %i to i64
+  br label %L3_header
+
+; CHECK: L3_header:
+; CHECK: %[[TRUNC:.*]] = trunc i64 %[[INDVAR]] to i32
+L3_header:
+  br i1 undef, label %L3_latch, label %L2_exiting_1
+
+L3_latch:
+  br i1 undef, label %L3_header, label %L2_exiting_2
+
+; CHECK: L2_exiting_1:
+; CHECK: %{{.*}} = phi i32 [ %[[TRUNC]], %L3_header ]
+L2_exiting_1:
+  br i1 undef, label %L2_latch, label %L1_latch
+
+; CHECK: L2_exiting_2:
+; CHECK: %{{.*}} = phi i32 [ %[[TRUNC]], %L3_latch ]
+L2_exiting_2:
+  br i1 undef, label %L2_latch, label %L1_latch
+
+L2_latch:
+  %i_next = add nsw i32 %i, 1
+  br label %L2_header
+
+L1_latch:
+  %i_lcssa = phi i32 [ %i, %L2_exiting_1 ], [ %i, %L2_exiting_2 ]
+  br i1 undef, label %exit, label %L1_header
+
+exit:
+  ret void
+}