diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -161,27 +161,42 @@
       // If we already inserted something for this BB, don't reprocess it.
       if (SSAUpdate.HasValueForBlock(ExitBB))
         continue;
+
+      PHINode *PN = nullptr;
+      // If ExitBB already contains a phi with a constant incoming value, re-use
+      // it instead of creating a new phi.
+      for (PHINode &ExistingPN : ExitBB->phis()) {
+        if (ExistingPN.hasConstantValue() == I) {
+          PN = &ExistingPN;
+          // LCSSA construction code assumes the phi to be the first in the
+          // block.
+          PN->moveBefore(&ExitBB->front());
+          break;
+        }
+      }
       Builder.SetInsertPoint(&ExitBB->front());
-      PHINode *PN = Builder.CreatePHI(I->getType(), PredCache.size(ExitBB),
-                                      I->getName() + ".lcssa");
-      // Get the debug location from the original instruction.
-      PN->setDebugLoc(I->getDebugLoc());
-
-      // Add inputs from inside the loop for this PHI. This is valid
-      // because `I` dominates `ExitBB` (checked above).  This implies
-      // that every incoming block/edge is dominated by `I` as well,
-      // i.e. we can add uses of `I` to those incoming edges/append to the incoming
-      // blocks without violating the SSA dominance property.
-      for (BasicBlock *Pred : PredCache.get(ExitBB)) {
-        PN->addIncoming(I, Pred);
-
-        // If the exit block has a predecessor not within the loop, arrange for
-        // the incoming value use corresponding to that predecessor to be
-        // rewritten in terms of a different LCSSA PHI.
-        if (!L->contains(Pred))
-          UsesToRewrite.push_back(
-              &PN->getOperandUse(PN->getOperandNumForIncomingValue(
-                  PN->getNumIncomingValues() - 1)));
+      if (!PN) {
+        PN = Builder.CreatePHI(I->getType(), PredCache.size(ExitBB),
+                               I->getName() + ".lcssa");
+        // Get the debug location from the original instruction.
+        PN->setDebugLoc(I->getDebugLoc());
+
+        // Add inputs from inside the loop for this PHI. This is valid
+        // because `I` dominates `ExitBB` (checked above).  This implies
+        // that every incoming block/edge is dominated by `I` as well,
+        // i.e. we can add uses of `I` to those incoming edges/append to the
+        // incoming blocks without violating the SSA dominance property.
+        for (BasicBlock *Pred : PredCache.get(ExitBB)) {
+          PN->addIncoming(I, Pred);
+        }
+
+        for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
+          // If the exit block has a predecessor not within the loop, arrange
+          // for the incoming value use corresponding to that predecessor to be
+          // rewritten in terms of a different LCSSA PHI.
+          if (!L->contains(PN->getIncomingBlock(I)))
+            UsesToRewrite.push_back(&PN->getOperandUse(I));
+        }
       }
 
       AddedPHIs.push_back(PN);
diff --git a/llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll b/llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
--- a/llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
+++ b/llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
@@ -86,3 +86,59 @@
   %res.lcssa2 = phi i64 [ %res.lcssa, %loop1.latch ]
   ret i64 %res.lcssa2
 }
+
+; Check that it does not crash because the incoming values of an LCSSA phi are
+; equal.
+define void @pr57000(i64 %a) {
+; CHECK-LABEL: @pr57000(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP_1_OUTER:%.*]]
+; CHECK:       loop.1.loopexit:
+; CHECK-NEXT:    br label [[LOOP_1_OUTER]]
+; CHECK:       loop.1.outer:
+; CHECK-NEXT:    br label [[LOOP_1:%.*]]
+; CHECK:       loop.1:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sle i64 [[A:%.*]], 2546175499358690212
+; CHECK-NEXT:    [[CMP_EXT:%.*]] = zext i1 [[CMP]] to i8
+; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP_1]], label [[LOOP_2_HEADER_PREHEADER:%.*]]
+; CHECK:       loop.2.header.preheader:
+; CHECK-NEXT:    [[CMP_LCSSA:%.*]] = phi i1 [ [[CMP]], [[LOOP_1]] ]
+; CHECK-NEXT:    [[CMP_EXT_LCSSA:%.*]] = phi i8 [ [[CMP_EXT]], [[LOOP_1]] ]
+; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER:%.*]]
+; CHECK:       loop.2.header.outer:
+; CHECK-NEXT:    br label [[LOOP_2_HEADER:%.*]]
+; CHECK:       loop.2.header:
+; CHECK-NEXT:    switch i8 [[CMP_EXT_LCSSA]], label [[LOOP_1_LOOPEXIT:%.*]] [
+; CHECK-NEXT:    i8 -1, label [[LOOP_2_LATCH:%.*]]
+; CHECK-NEXT:    i8 1, label [[LOOP_2_LATCH]]
+; CHECK-NEXT:    i8 4, label [[LOOP_2_HEADER]]
+; CHECK-NEXT:    ]
+; CHECK:       loop.2.latch:
+; CHECK-NEXT:    [[CMP_TRUNC_LCSSA1:%.*]] = phi i1 [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ], [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ]
+; CHECK-NEXT:    call void @use(i1 [[CMP_TRUNC_LCSSA1]])
+; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER]]
+;
+entry:
+  br label %loop.1
+
+loop.1:
+  %p.1 = phi i1 [ 0 , %entry ], [ %p.1, %loop.1 ], [ %p.2, %loop.2.header ]
+  %cmp = icmp sle i64 %a, 2546175499358690212
+  %cmp.ext = zext i1 %cmp to i8
+  br i1 %cmp, label %loop.1, label %loop.2.header
+
+loop.2.header:
+  %p.2 = phi i1 [ %p.1, %loop.1 ], [ %p.2, %loop.2.header ], [ %cmp, %loop.2.latch ]
+  %cmp.trunc = trunc i8 %cmp.ext to i1
+  switch i8 %cmp.ext, label %loop.1 [
+  i8 -1, label %loop.2.latch
+  i8 1, label %loop.2.latch
+  i8 4, label %loop.2.header
+  ]
+
+loop.2.latch:
+  call void @use(i1 %cmp.trunc)
+  br label %loop.2.header
+}
+
+declare void @use(i1)
diff --git a/llvm/test/Transforms/LoopUnroll/rebuild_lcssa.ll b/llvm/test/Transforms/LoopUnroll/rebuild_lcssa.ll
--- a/llvm/test/Transforms/LoopUnroll/rebuild_lcssa.ll
+++ b/llvm/test/Transforms/LoopUnroll/rebuild_lcssa.ll
@@ -246,7 +246,6 @@
 ; CHECK-NEXT:    [[A_LCSSA:%.*]] = phi i32 [ [[A_LCSSA]], [[INNER3]] ], [ [[A]], [[INNER2_INDIRECT_EXIT]] ]
 ; CHECK-NEXT:    br i1 true, label [[OUTER_LATCH_LOOPEXIT:%.*]], label [[INNER3]]
 ; CHECK:       outer_latch.loopexit:
-; CHECK-NEXT:    [[A_LCSSA_LCSSA2:%.*]] = phi i32 [ [[A_LCSSA]], [[INNER3]] ]
 ; CHECK-NEXT:    [[A_LCSSA_LCSSA:%.*]] = phi i32 [ [[A_LCSSA]], [[INNER3]] ]
 ; CHECK-NEXT:    br label [[OUTER_LATCH:%.*]]
 ; CHECK:       outer_latch:
diff --git a/llvm/test/Transforms/LoopVectorize/create-induction-resume.ll b/llvm/test/Transforms/LoopVectorize/create-induction-resume.ll
--- a/llvm/test/Transforms/LoopVectorize/create-induction-resume.ll
+++ b/llvm/test/Transforms/LoopVectorize/create-induction-resume.ll
@@ -29,7 +29,6 @@
 ; CHECK:       L1.early.exit:
 ; CHECK-NEXT:    ret void
 ; CHECK:       L1.exit:
-; CHECK-NEXT:    [[INDUCTION_IV_LCSSA3:%.*]] = phi i32 [ [[INDUCTION_IV]], [[L1_BACKEDGE]] ]
 ; CHECK-NEXT:    [[INDUCTION_IV_LCSSA1:%.*]] = phi i32 [ [[INDUCTION_IV]], [[L1_BACKEDGE]] ]
 ; CHECK-NEXT:    [[L1_EXIT_VAL:%.*]] = phi i32 [ [[L1_SUM_NEXT]], [[L1_BACKEDGE]] ]
 ; CHECK-NEXT:    br label [[L2_HEADER:%.*]]
diff --git a/llvm/test/Transforms/LoopVectorize/skeleton-lcssa-crash.ll b/llvm/test/Transforms/LoopVectorize/skeleton-lcssa-crash.ll
--- a/llvm/test/Transforms/LoopVectorize/skeleton-lcssa-crash.ll
+++ b/llvm/test/Transforms/LoopVectorize/skeleton-lcssa-crash.ll
@@ -23,7 +23,6 @@
 ; CHECK-NEXT:    [[C_3:%.*]] = call i1 @cond()
 ; CHECK-NEXT:    br i1 [[C_3]], label [[LOOP_3_PREHEADER:%.*]], label [[INNER_LATCH:%.*]]
 ; CHECK:       loop.3.preheader:
-; CHECK-NEXT:    [[L_1_LCSSA7:%.*]] = phi ptr [ [[L_1]], [[INNER_BB]] ]
 ; CHECK-NEXT:    [[L_1_LCSSA:%.*]] = phi ptr [ [[L_1]], [[INNER_BB]] ]
 ; CHECK-NEXT:    [[L_2_LCSSA:%.*]] = phi ptr [ [[L_2]], [[INNER_BB]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[N:%.*]], 1
@@ -34,7 +33,7 @@
 ; CHECK-NEXT:    [[UGLYGEP3:%.*]] = getelementptr i8, ptr [[L_1_LCSSA]], i64 2
 ; CHECK-NEXT:    [[TMP1:%.*]] = shl i64 [[N]], 1
 ; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[TMP1]], 4
-; CHECK-NEXT:    [[UGLYGEP6:%.*]] = getelementptr i8, ptr [[L_1_LCSSA7]], i64 [[TMP2]]
+; CHECK-NEXT:    [[UGLYGEP6:%.*]] = getelementptr i8, ptr [[L_1_LCSSA]], i64 [[TMP2]]
 ; CHECK-NEXT:    [[BOUND0:%.*]] = icmp ult ptr [[L_2_LCSSA]], [[UGLYGEP6]]
 ; CHECK-NEXT:    [[BOUND1:%.*]] = icmp ult ptr [[UGLYGEP3]], [[UGLYGEP]]
 ; CHECK-NEXT:    [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
@@ -141,14 +140,13 @@
 ; CHECK-NEXT:    [[INDVAR_NEXT]] = add i32 [[INDVAR]], 1
 ; CHECK-NEXT:    br i1 [[C_1]], label [[LOOP_2]], label [[LOOP_3_PH:%.*]]
 ; CHECK:       loop.3.ph:
-; CHECK-NEXT:    [[INDVAR_LCSSA1:%.*]] = phi i32 [ [[INDVAR]], [[LOOP_2]] ]
 ; CHECK-NEXT:    [[INDVAR_LCSSA:%.*]] = phi i32 [ [[INDVAR]], [[LOOP_2]] ]
 ; CHECK-NEXT:    [[IV_1_LCSSA:%.*]] = phi i64 [ [[IV_1]], [[LOOP_2]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i64 [[IV_1_LCSSA]], 4294967295
-; CHECK-NEXT:    [[TMP1:%.*]] = mul i32 [[INDVAR_LCSSA1]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = mul i32 [[INDVAR_LCSSA]], -1
 ; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[TMP1]], 1000
-; CHECK-NEXT:    [[SMIN2:%.*]] = call i32 @llvm.smin.i32(i32 [[TMP2]], i32 1)
-; CHECK-NEXT:    [[TMP3:%.*]] = sub i32 [[TMP2]], [[SMIN2]]
+; CHECK-NEXT:    [[SMIN1:%.*]] = call i32 @llvm.smin.i32(i32 [[TMP2]], i32 1)
+; CHECK-NEXT:    [[TMP3:%.*]] = sub i32 [[TMP2]], [[SMIN1]]
 ; CHECK-NEXT:    [[TMP4:%.*]] = zext i32 [[TMP3]] to i64
 ; CHECK-NEXT:    [[TMP5:%.*]] = add nuw nsw i64 [[TMP4]], 1
 ; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP5]], 2