diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6733,7 +6733,14 @@
     return true;
 
   if (SinkCommon && Options.SinkCommonInsts)
-    Changed |= SinkCommonCodeFromPredecessors(BB, DTU);
+    if (SinkCommonCodeFromPredecessors(BB, DTU)) {
+      // SinkCommonCodeFromPredecessors() does not automatically CSE PHI's,
+      // so we may now how duplicate PHI's.
+      // Let's rerun EliminateDuplicatePHINodes() first,
+      // before FoldTwoEntryPHINode() potentially converts them into select's,
+      // after which we'd need a whole EarlyCSE pass run to cleanup them.
+      return true;
+    }
 
   IRBuilder<> Builder(BB);
 
diff --git a/llvm/test/Transforms/PGOProfile/cspgo_profile_summary.ll b/llvm/test/Transforms/PGOProfile/cspgo_profile_summary.ll
--- a/llvm/test/Transforms/PGOProfile/cspgo_profile_summary.ll
+++ b/llvm/test/Transforms/PGOProfile/cspgo_profile_summary.ll
@@ -67,10 +67,10 @@
   ret void
 }
 ; PGOSUMMARY-LABEL: @bar
-; PGOSUMMARY: %odd.sink{{[0-9]*}} = select i1 %tobool{{[0-9]*}}, i32* @even, i32* @odd
+; PGOSUMMARY: %even.odd = select i1 %tobool{{[0-9]*}}, i32* @even, i32* @odd
 ; PGOSUMMARY-SAME: !prof ![[BW_PGO_BAR:[0-9]+]]
 ; CSPGOSUMMARY-LABEL: @bar
-; CSPGOSUMMARY: %odd.sink{{[0-9]*}} = select i1 %tobool{{[0-9]*}}, i32* @even, i32* @odd
+; CSPGOSUMMARY: %even.odd = select i1 %tobool{{[0-9]*}}, i32* @even, i32* @odd
 ; CSPGOSUMMARY-SAME: !prof ![[BW_CSPGO_BAR:[0-9]+]]
 
 define internal fastcc i32 @cond(i32 %i) {
@@ -103,9 +103,9 @@
   ret void
 }
 ; CSPGOSUMMARY-LABEL: @foo
-; CSPGOSUMMARY: %odd.sink.i{{[0-9]*}} = select i1 %tobool.i{{[0-9]*}}, i32* @even, i32* @odd
+; CSPGOSUMMARY: %even.odd.i = select i1 %tobool.i{{[0-9]*}}, i32* @even, i32* @odd
 ; CSPGOSUMMARY-SAME: !prof ![[BW_CSPGO_BAR]]
-; CSPGOSUMMARY: %odd.sink.i{{[0-9]*}} = select i1 %tobool.i{{[0-9]*}}, i32* @even, i32* @odd
+; CSPGOSUMMARY: %even.odd.i2 = select i1 %tobool.i{{[0-9]*}}, i32* @even, i32* @odd
 ; CSPGOSUMMARY-SAME: !prof ![[BW_CSPGO_BAR]]
 
 declare dso_local i32 @bar_m(i32)
diff --git a/llvm/test/Transforms/PhaseOrdering/X86/earlycse-after-simplifycfg-two-entry-phi-node-folding.ll b/llvm/test/Transforms/PhaseOrdering/X86/earlycse-after-simplifycfg-two-entry-phi-node-folding.ll
--- a/llvm/test/Transforms/PhaseOrdering/X86/earlycse-after-simplifycfg-two-entry-phi-node-folding.ll
+++ b/llvm/test/Transforms/PhaseOrdering/X86/earlycse-after-simplifycfg-two-entry-phi-node-folding.ll
@@ -5,17 +5,17 @@
 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"
 
+; PR51092: SimplifyCFG might produce duplicate PHI's/select's.
+; We need to deduplicate them so that further transformations are possible.
 define dso_local void @foo(i32* %in, i64 %lo, i64 %hi, i32 %ishi) #0 {
 ; ALL-LABEL: @foo(
 ; ALL-NEXT:  entry:
 ; ALL-NEXT:    [[TOBOOL_NOT:%.*]] = icmp eq i32 [[ISHI:%.*]], 0
-; ALL-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds i32, i32* [[IN:%.*]], i64 [[LO:%.*]]
-; ALL-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, i32* [[IN]], i64 [[HI:%.*]]
-; ALL-NEXT:    [[ARRAYIDX1_SINK1:%.*]] = select i1 [[TOBOOL_NOT]], i32* [[ARRAYIDX1]], i32* [[ARRAYIDX]]
-; ALL-NEXT:    [[ARRAYIDX1_SINK:%.*]] = select i1 [[TOBOOL_NOT]], i32* [[ARRAYIDX1]], i32* [[ARRAYIDX]]
-; ALL-NEXT:    [[ARRAYVAL2:%.*]] = load i32, i32* [[ARRAYIDX1_SINK1]], align 4
+; ALL-NEXT:    [[LO_HI:%.*]] = select i1 [[TOBOOL_NOT]], i64 [[LO:%.*]], i64 [[HI:%.*]]
+; ALL-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds i32, i32* [[IN:%.*]], i64 [[LO_HI]]
+; ALL-NEXT:    [[ARRAYVAL2:%.*]] = load i32, i32* [[ARRAYIDX1]], align 4
 ; ALL-NEXT:    [[INC2:%.*]] = add nsw i32 [[ARRAYVAL2]], 1
-; ALL-NEXT:    store i32 [[INC2]], i32* [[ARRAYIDX1_SINK]], align 4
+; ALL-NEXT:    store i32 [[INC2]], i32* [[ARRAYIDX1]], align 4
 ; ALL-NEXT:    ret void
 ;
 entry:
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
--- a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
@@ -71,10 +71,9 @@
 define i32 @test3(i1 zeroext %flag, i32 %x, i32 %y) {
 ; CHECK-LABEL: @test3(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[Y_SINK1:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
-; CHECK-NEXT:    [[Y_SINK:%.*]] = select i1 [[FLAG]], i32 [[X]], i32 [[Y]]
-; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[Y_SINK1]], i32 0) #[[ATTR0:[0-9]+]]
-; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[Y_SINK]], i32 1) #[[ATTR0]]
+; CHECK-NEXT:    [[X_Y:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 0) #[[ATTR0:[0-9]+]]
+; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 1) #[[ATTR0]]
 ; CHECK-NEXT:    [[RET:%.*]] = add i32 [[X1]], [[Y1]]
 ; CHECK-NEXT:    ret i32 [[RET]]
 ;
@@ -102,8 +101,8 @@
 define i32 @test4(i1 zeroext %flag, i32 %x, i32* %y) {
 ; CHECK-LABEL: @test4(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
-; CHECK-NEXT:    [[B:%.*]] = add i32 [[X:%.*]], [[DOTSINK]]
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
+; CHECK-NEXT:    [[B:%.*]] = add i32 [[X:%.*]], [[DOT]]
 ; CHECK-NEXT:    store i32 [[B]], i32* [[Y:%.*]], align 4
 ; CHECK-NEXT:    ret i32 1
 ;
@@ -161,8 +160,8 @@
 define i32 @test6(i1 zeroext %flag, i32 %x, i32* %y) {
 ; CHECK-LABEL: @test6(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
-; CHECK-NEXT:    [[B:%.*]] = add i32 [[X:%.*]], [[DOTSINK]]
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
+; CHECK-NEXT:    [[B:%.*]] = add i32 [[X:%.*]], [[DOT]]
 ; CHECK-NEXT:    store volatile i32 [[B]], i32* [[Y:%.*]], align 4
 ; CHECK-NEXT:    ret i32 1
 ;
@@ -187,9 +186,9 @@
 define i32 @test7(i1 zeroext %flag, i32 %x, i32* %y) {
 ; CHECK-LABEL: @test7(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
 ; CHECK-NEXT:    [[W:%.*]] = load volatile i32, i32* [[Y:%.*]], align 4
-; CHECK-NEXT:    [[B:%.*]] = add i32 [[W]], [[DOTSINK]]
+; CHECK-NEXT:    [[B:%.*]] = add i32 [[W]], [[DOT]]
 ; CHECK-NEXT:    store volatile i32 [[B]], i32* [[Y]], align 4
 ; CHECK-NEXT:    ret i32 1
 ;
@@ -413,9 +412,9 @@
 define i32 @test13(i1 zeroext %flag, i32 %x, i32* %y) {
 ; CHECK-LABEL: @test13(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 5, i32 7
 ; CHECK-NEXT:    [[W:%.*]] = load volatile i32, i32* [[Y:%.*]], align 4
-; CHECK-NEXT:    [[B:%.*]] = add i32 [[W]], [[DOTSINK]]
+; CHECK-NEXT:    [[B:%.*]] = add i32 [[W]], [[DOT]]
 ; CHECK-NEXT:    store volatile i32 [[B]], i32* [[Y]], align 4, !tbaa [[TBAA4:![0-9]+]]
 ; CHECK-NEXT:    ret i32 1
 ;
@@ -449,8 +448,8 @@
 define i32 @test13a(i1 zeroext %flag, i32 %w, i32 %x, i32 %y) {
 ; CHECK-LABEL: @test13a(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[Y_SINK:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
-; CHECK-NEXT:    [[SV2:%.*]] = call i32 @bar(i32 [[Y_SINK]])
+; CHECK-NEXT:    [[X_Y:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[SV2:%.*]] = call i32 @bar(i32 [[X_Y]])
 ; CHECK-NEXT:    ret i32 1
 ;
 entry:
@@ -475,12 +474,12 @@
 define i32 @test14(i1 zeroext %flag, i32 %w, i32 %x, i32 %y, %struct.anon* %s) {
 ; CHECK-LABEL: @test14(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK1:%.*]] = select i1 [[FLAG:%.*]], i32 1, i32 4
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG]], i32 56, i32 57
-; CHECK-NEXT:    [[DUMMY2:%.*]] = add i32 [[X:%.*]], [[DOTSINK1]]
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 1, i32 4
+; CHECK-NEXT:    [[DOT2:%.*]] = select i1 [[FLAG]], i32 56, i32 57
+; CHECK-NEXT:    [[DUMMY2:%.*]] = add i32 [[X:%.*]], [[DOT]]
 ; CHECK-NEXT:    [[GEPB:%.*]] = getelementptr inbounds [[STRUCT_ANON:%.*]], %struct.anon* [[S:%.*]], i32 0, i32 1
 ; CHECK-NEXT:    [[SV2:%.*]] = load i32, i32* [[GEPB]], align 4
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[SV2]], [[DOTSINK]]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[SV2]], [[DOT2]]
 ; CHECK-NEXT:    ret i32 1
 ;
 entry:
@@ -959,10 +958,9 @@
 define i32 @test_pr30373a(i1 zeroext %flag, i32 %x, i32 %y) {
 ; CHECK-LABEL: @test_pr30373a(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[Y_SINK1:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
-; CHECK-NEXT:    [[Y_SINK:%.*]] = select i1 [[FLAG]], i32 [[X]], i32 [[Y]]
-; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[Y_SINK1]], i32 0) #[[ATTR0]]
-; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[Y_SINK]], i32 1) #[[ATTR0]]
+; CHECK-NEXT:    [[X_Y:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 0) #[[ATTR0]]
+; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 1) #[[ATTR0]]
 ; CHECK-NEXT:    [[Z1:%.*]] = lshr i32 [[Y1]], 8
 ; CHECK-NEXT:    [[RET:%.*]] = add i32 [[X1]], [[Z1]]
 ; CHECK-NEXT:    ret i32 [[RET]]
@@ -993,10 +991,9 @@
 define i32 @test_pr30373b(i1 zeroext %flag, i32 %x, i32 %y) {
 ; CHECK-LABEL: @test_pr30373b(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[Y_SINK1:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
-; CHECK-NEXT:    [[Y_SINK:%.*]] = select i1 [[FLAG]], i32 [[X]], i32 [[Y]]
-; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[Y_SINK1]], i32 0) #[[ATTR0]]
-; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[Y_SINK]], i32 1) #[[ATTR0]]
+; CHECK-NEXT:    [[X_Y:%.*]] = select i1 [[FLAG:%.*]], i32 [[X:%.*]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[X1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 0) #[[ATTR0]]
+; CHECK-NEXT:    [[Y1:%.*]] = call i32 @foo(i32 [[X_Y]], i32 1) #[[ATTR0]]
 ; CHECK-NEXT:    [[Z1:%.*]] = lshr i32 [[Y1]], 8
 ; CHECK-NEXT:    [[RET:%.*]] = add i32 [[X1]], [[Z1]]
 ; CHECK-NEXT:    ret i32 [[RET]]
@@ -1264,8 +1261,8 @@
 define i32 @test_insertvalue(i1 zeroext %flag, %T %P) {
 ; CHECK-LABEL: @test_insertvalue(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[DOTSINK:%.*]] = select i1 [[FLAG:%.*]], i32 0, i32 1
-; CHECK-NEXT:    [[T2:%.*]] = insertvalue [[T:%.*]] [[P:%.*]], i32 [[DOTSINK]], 0
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[FLAG:%.*]], i32 0, i32 1
+; CHECK-NEXT:    [[T2:%.*]] = insertvalue [[T:%.*]] [[P:%.*]], i32 [[DOT]], 0
 ; CHECK-NEXT:    ret i32 1
 ;
 entry:
@@ -1410,8 +1407,8 @@
 define void @indirect_caller(i1 %c, i32 %v, void (i32)* %foo, void (i32)* %bar) {
 ; CHECK-LABEL: @indirect_caller(
 ; CHECK-NEXT:  end:
-; CHECK-NEXT:    [[BAR_SINK:%.*]] = select i1 [[C:%.*]], void (i32)* [[FOO:%.*]], void (i32)* [[BAR:%.*]]
-; CHECK-NEXT:    tail call void [[BAR_SINK]](i32 [[V:%.*]])
+; CHECK-NEXT:    [[FOO_BAR:%.*]] = select i1 [[C:%.*]], void (i32)* [[FOO:%.*]], void (i32)* [[BAR:%.*]]
+; CHECK-NEXT:    tail call void [[FOO_BAR]](i32 [[V:%.*]])
 ; CHECK-NEXT:    ret void
 ;
   br i1 %c, label %call_foo, label %call_bar