Index: lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- lib/Analysis/ScalarEvolutionExpander.cpp
+++ lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1737,7 +1737,20 @@
 
     // Fold constant phis. They may be congruent to other constant phis and
     // would confuse the logic below that expects proper IVs.
-    if (Value *V = SimplifyInstruction(Phi, DL, &SE.TLI, &SE.DT, &SE.AC)) {
+    Value *V = SimplifyInstruction(Phi, DL, &SE.TLI, &SE.DT, &SE.AC);
+    if (!V) {
+      const SCEVConstant *Const = nullptr;
+      if (SE.isSCEVable(Phi->getType())) {
+        Const = dyn_cast<SCEVConstant>(SE.getSCEV(Phi));
+        if (Const) {
+          V = Const->getValue();
+          if (V->getType() != Phi->getType())
+            continue;
+        }
+      }
+    }
+
+    if (V) {
       Phi->replaceAllUsesWith(V);
       DeadInsts.emplace_back(Phi);
       ++NumElim;
Index: test/Transforms/IndVarSimplify/const_phi.ll
===================================================================
--- /dev/null
+++ test/Transforms/IndVarSimplify/const_phi.ll
@@ -0,0 +1,33 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; PR25372
+; We can compute the expression of %storemerge, and that is a SCEV
+; constant. However, instcombine can't deduce this, so we can
+; potentially end up trying to handle a constant when replacing 
+; congruent IVs.
+
+; CHECK-LABEL: crash
+define void @crash() {
+entry:
+  br i1 false, label %not_taken, label %pre
+
+not_taken:
+  br label %pre
+
+pre:
+; %phi0.pre and %phi1.pre are evaluated by SCEV to constant 0.
+  %phi0.pre = phi i32 [ 0, %entry ], [ 2, %not_taken ]
+  %phi1.pre = phi i32 [ 0, %entry ], [ 1, %not_taken ]
+  br label %loop
+
+loop:
+; %phi0 and %phi1 are evaluated by SCEV to constant 0.
+  %phi0 = phi i32 [ 0, %loop ], [ %phi0.pre, %pre ]
+  %phi1 = phi i32 [ 0, %loop ], [ %phi1.pre, %pre ]
+  br i1 undef, label %exit, label %loop
+
+exit:
+  ret void
+}