Index: llvm/test/Transforms/SimplifyCFG/branch-fold.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/branch-fold.ll
+++ llvm/test/Transforms/SimplifyCFG/branch-fold.ll
@@ -114,3 +114,37 @@
   call void @foo()
   ret void
 }
+
+define i8 @common_pred(i8 noundef %arg, i1 %c1, i1 %c2) {
+; CHECK-LABEL: @common_pred(
+; CHECK-NEXT:  Pred:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br i1 [[C1:%.*]], label [[COMMONPRED:%.*]], label [[BB:%.*]]
+; CHECK:       CommonPred:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br i1 [[C2:%.*]], label [[SUCC:%.*]], label [[BB]]
+; CHECK:       BB:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 0, [[PRED:%.*]] ], [ 1, [[COMMONPRED]] ]
+; CHECK-NEXT:    br label [[SUCC]]
+; CHECK:       Succ:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[BB]] ], [ 4, [[COMMONPRED]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+Pred:
+call void @dummy()
+  br i1 %c1, label %CommonPred, label %BB
+
+CommonPred:
+call void @dummy()
+  br i1 %c2, label %Succ, label %BB
+
+BB:
+  %phi1 = phi i8 [ 0, %Pred ], [1, %CommonPred]
+  br label %Succ
+
+Succ:
+  %phi2 = phi i8 [ %phi1, %BB ], [ 4, %CommonPred ]
+  ret i8 %phi2
+}
+
+declare void @dummy()
Index: llvm/test/Transforms/SimplifyCFG/merge-phis-in-switch.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/merge-phis-in-switch.ll
@@ -0,0 +1,335 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
+
+; Test a bunch of cases where the combination of phis in switch should be merged into one phi
+
+declare void @use(i8)
+
+define i8 @phis_of_switch_minimal(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @phis_of_switch_minimal
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE01:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[END:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE01]]
+; CHECK:       case01:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 2, [[CASE1]] ], [ 1, [[START:%.*]] ]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[CASE01]] ], [ 3, [[START]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case01
+  i8 1, label %case1
+  i8 2, label %end
+  ]
+unreachable:
+  unreachable
+case1:
+  br label %case01
+
+case01:
+  %phi1 = phi i8 [ 2, %case1 ], [1, %start]
+  br label %end
+
+end:
+  %phi2 = phi i8 [ %phi1, %case01 ], [ 3, %start ]
+  ret i8 %phi2
+}
+
+define i8 @phis_of_switch(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @phis_of_switch
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE012:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[CASE2:%.*]]
+; CHECK-NEXT:    i8 3, label [[END:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case012:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 3, [[CASE2]] ], [ 2, [[CASE1]] ], [ 1, [[START:%.*]] ]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[CASE012]] ], [ 4, [[START]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case012
+  i8 1, label %case1
+  i8 2, label %case2
+  i8 3, label %end
+  ]
+unreachable:
+  unreachable
+case1:
+  br label %case012
+
+case2:
+  br label %case012
+
+case012:
+  %phi1 = phi i8 [ 3, %case2 ], [ 2, %case1 ], [1, %start]
+  br label %end
+
+end:
+  %phi2 = phi i8 [ %phi1, %case012 ], [ 4, %start ]
+  ret i8 %phi2
+}
+
+define i8 @multiple_phis_of_switch(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @multiple_phis_of_switch
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE012:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[CASE2:%.*]]
+; CHECK-NEXT:    i8 3, label [[END:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case012:
+; CHECK-NEXT:    [[PHI1_1:%.*]] = phi i8 [ 3, [[CASE2]] ], [ 2, [[CASE1]] ], [ 1, [[START:%.*]] ]
+; CHECK-NEXT:    [[PHI1_2:%.*]] = phi i8 [ 6, [[CASE2]] ], [ 5, [[CASE1]] ], [ 4, [[START]] ]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[PHI2_1:%.*]] = phi i8 [ [[PHI1_1]], [[CASE012]] ], [ 4, [[START]] ]
+; CHECK-NEXT:    [[PHI2_2:%.*]] = phi i8 [ [[PHI1_1]], [[CASE012]] ], [ 5, [[START]] ]
+; CHECK-NEXT:    [[PHI2_3:%.*]] = phi i8 [ [[PHI1_2]], [[CASE012]] ], [ 3, [[START]] ]
+; CHECK-NEXT:    call void @use(i8 [[PHI2_1]])
+; CHECK-NEXT:    call void @use(i8 [[PHI2_2]])
+; CHECK-NEXT:    call void @use(i8 [[PHI2_3]])
+; CHECK-NEXT:    ret i8 [[PHI2_1]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case012
+  i8 1, label %case1
+  i8 2, label %case2
+  i8 3, label %end
+  ]
+unreachable:
+  unreachable
+case1:
+  br label %case012
+
+case2:
+  br label %case012
+
+case012:
+  %phi1_1 = phi i8 [ 3, %case2 ], [ 2, %case1 ], [1, %start]
+  %phi1_2 = phi i8 [ 6, %case2 ], [ 5, %case1 ], [4, %start]
+  br label %end
+
+end:
+  %phi2_1 = phi i8 [ %phi1_1, %case012 ], [ 4, %start ]
+  %phi2_2 = phi i8 [ %phi1_1, %case012 ], [ 5, %start ]
+  %phi2_3 = phi i8 [ %phi1_2, %case012 ], [ 3, %start ]
+  call void @use(i8 %phi2_1)
+  call void @use(i8 %phi2_2)
+  call void @use(i8 %phi2_3)
+  ret i8 %phi2_1
+}
+
+define i8 @phis_of_switch_multiple_stage0(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @phis_of_switch_multiple_stage0
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[CASE2:%.*]]
+; CHECK-NEXT:    i8 3, label [[CASE0123:%.*]]
+; CHECK-NEXT:    i8 4, label [[CASE01234:%.*]]
+; CHECK-NEXT:    i8 5, label [[END:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    br label [[CASE0123]]
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE0123]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[CASE0123]]
+; CHECK:       case0123:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 4, [[START:%.*]] ], [ 3, [[CASE2]] ], [ 2, [[CASE1]] ], [ 1, [[CASE0]] ]
+; CHECK-NEXT:    br label [[CASE01234]]
+; CHECK:       case01234:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[CASE0123]] ], [ 5, [[START]] ]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[PHI3:%.*]] = phi i8 [ [[PHI2]], [[CASE01234]] ], [ 6, [[START]] ]
+; CHECK-NEXT:    ret i8 [[PHI3]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case0
+  i8 1, label %case1
+  i8 2, label %case2
+  i8 3, label %case0123
+  i8 4, label %case01234
+  i8 5, label %end
+  ]
+unreachable:
+  unreachable
+
+case0:
+  br label %case0123
+
+case1:
+  br label %case0123
+
+case2:
+  br label %case0123
+
+case0123:
+  %phi1 = phi i8 [4, %start], [ 3, %case2 ], [ 2, %case1 ], [ 1, %case0 ]
+  br label %case01234
+
+case01234:
+  %phi2 = phi i8 [ %phi1, %case0123 ], [ 5, %start ]
+  br label %end
+
+end:
+  %phi3 = phi i8 [ %phi2, %case01234 ], [6, %start]
+  ret i8 %phi3
+}
+
+define i8 @phis_of_switch_multiple_stage1(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @phis_of_switch_multiple_stage1
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[CASE012:%.*]]
+; CHECK-NEXT:    i8 3, label [[CASE3:%.*]]
+; CHECK-NEXT:    i8 4, label [[CASE4:%.*]]
+; CHECK-NEXT:    i8 5, label [[CASE345:%.*]]
+; CHECK-NEXT:    i8 6, label [[CASE0123456:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case012:
+; CHECK-NEXT:    [[PHI123:%.*]] = phi i8 [ 3, [[START:%.*]] ], [ 2, [[CASE1]] ], [ 1, [[CASE0]] ]
+; CHECK-NEXT:    br label [[CASE0123456]]
+; CHECK:       case3:
+; CHECK-NEXT:    br label [[CASE345]]
+; CHECK:       case4:
+; CHECK-NEXT:    br label [[CASE345]]
+; CHECK:       case345:
+; CHECK-NEXT:    [[PHI456:%.*]] = phi i8 [ 6, [[START]] ], [ 5, [[CASE4]] ], [ 4, [[CASE3]] ]
+; CHECK-NEXT:    br label [[CASE0123456]]
+; CHECK:       case0123456:
+; CHECK-NEXT:    [[PHI1234567:%.*]] = phi i8 [ 7, [[START]] ], [ [[PHI456]], [[CASE345]] ], [ [[PHI123]], [[CASE012]] ]
+; CHECK-NEXT:    ret i8 [[PHI1234567]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case0
+  i8 1, label %case1
+  i8 2, label %case012
+  i8 3, label %case3
+  i8 4, label %case4
+  i8 5, label %case345
+  i8 6, label %case0123456
+  ]
+unreachable:
+  unreachable
+case0:
+  br label %case012
+
+case1:
+  br label %case012
+
+case012:
+  %phi123 = phi i8 [3, %start], [ 2, %case1 ], [ 1, %case0 ]
+  br label %case0123456
+
+case3:
+  br label %case345
+
+case4:
+  br label %case345
+
+case345:
+  %phi456 = phi i8 [6, %start], [ 5, %case4 ], [ 4, %case3 ]
+  br label %case0123456
+
+case0123456:
+  %phi1234567 = phi i8 [7, %start], [ %phi456, %case345 ], [ %phi123, %case012 ]
+  ret i8 %phi1234567
+
+}
+
+define i8 @phis_of_switch_extra_use_fail(i8 noundef %arg) {
+; CHECK-LABEL: define i8 @phis_of_switch_extra_use_fail
+; CHECK-SAME: (i8 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 0, label [[CASE012:%.*]]
+; CHECK-NEXT:    i8 1, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 2, label [[CASE2:%.*]]
+; CHECK-NEXT:    i8 3, label [[END:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case1:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[CASE012]]
+; CHECK:       case012:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 3, [[CASE2]] ], [ 2, [[CASE1]] ], [ 1, [[START:%.*]] ]
+; CHECK-NEXT:    call void @use(i8 [[PHI1]])
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[CASE012]] ], [ 4, [[START]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+start:
+  switch i8 %arg, label %unreachable [
+  i8 0, label %case012
+  i8 1, label %case1
+  i8 2, label %case2 i8 3, label %end
+  ]
+unreachable:
+  unreachable
+case1:
+  br label %case012
+
+case2:
+  br label %case012
+
+case012:
+  %phi1 = phi i8 [ 3, %case2 ], [ 2, %case1 ], [1, %start]
+  call void @use(i8 %phi1)
+  br label %end
+
+end:
+  %phi2 = phi i8 [ %phi1, %case012 ], [ 4, %start ]
+  ret i8 %phi2
+}
Index: llvm/test/Transforms/SimplifyCFG/multiple-phis.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/multiple-phis.ll
+++ llvm/test/Transforms/SimplifyCFG/multiple-phis.ll
@@ -1,4 +1,5 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+
 ; RUN: opt -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -keep-loops=false -S < %s | FileCheck %s
 ; RUN: opt -passes='simplifycfg<no-keep-loops>' -S < %s | FileCheck %s
 
@@ -7,11 +8,12 @@
 ; SimplifyCFG if-converts one of the phis, it should do both.
 
 define i32 @upper_bound(ptr %r, i32 %high, i32 %k) nounwind {
-; CHECK-LABEL: @upper_bound(
+; CHECK-LABEL: define i32 @upper_bound
+; CHECK-SAME: (ptr [[R:%.*]], i32 [[HIGH:%.*]], i32 [[K:%.*]]) #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[WHILE_COND:%.*]]
 ; CHECK:       while.cond:
-; CHECK-NEXT:    [[HIGH_ADDR_0:%.*]] = phi i32 [ [[HIGH:%.*]], [[ENTRY:%.*]] ], [ [[SPEC_SELECT:%.*]], [[WHILE_BODY:%.*]] ]
+; CHECK-NEXT:    [[HIGH_ADDR_0:%.*]] = phi i32 [ [[HIGH]], [[ENTRY:%.*]] ], [ [[SPEC_SELECT:%.*]], [[WHILE_BODY:%.*]] ]
 ; CHECK-NEXT:    [[LOW_0:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[SPEC_SELECT1:%.*]], [[WHILE_BODY]] ]
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[LOW_0]], [[HIGH_ADDR_0]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[WHILE_BODY]], label [[WHILE_END:%.*]]
@@ -19,9 +21,9 @@
 ; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[LOW_0]], [[HIGH_ADDR_0]]
 ; CHECK-NEXT:    [[DIV:%.*]] = udiv i32 [[ADD]], 2
 ; CHECK-NEXT:    [[IDXPROM:%.*]] = zext i32 [[DIV]] to i64
-; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[R:%.*]], i64 [[IDXPROM]]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[R]], i64 [[IDXPROM]]
 ; CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i32 [[K:%.*]], [[TMP0]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i32 [[K]], [[TMP0]]
 ; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[DIV]], 1
 ; CHECK-NEXT:    [[SPEC_SELECT]] = select i1 [[CMP1]], i32 [[DIV]], i32 [[HIGH_ADDR_0]]
 ; CHECK-NEXT:    [[SPEC_SELECT1]] = select i1 [[CMP1]], i32 [[LOW_0]], i32 [[ADD2]]
@@ -57,3 +59,285 @@
 while.end:                                        ; preds = %while.cond
   ret i32 %low.0
 }
+
+define i32 @merge0(i1 %c1, i1 %c2, i1 %c3) {
+; CHECK-LABEL: define i32 @merge0
+; CHECK-SAME: (i1 [[C1:%.*]], i1 [[C2:%.*]], i1 [[C3:%.*]]) {
+; CHECK-NEXT:    br i1 [[C1]], label [[IF1:%.*]], label [[ELSE1:%.*]]
+; CHECK:       if1:
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[C2]], i32 0, i32 1
+; CHECK-NEXT:    br label [[J1:%.*]]
+; CHECK:       else1:
+; CHECK-NEXT:    br i1 [[C3]], label [[J1]], label [[J2:%.*]]
+; CHECK:       j1:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i32 [ 2, [[ELSE1]] ], [ [[DOT]], [[IF1]] ]
+; CHECK-NEXT:    br label [[J2]]
+; CHECK:       j2:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i32 [ [[PHI1]], [[J1]] ], [ 3, [[ELSE1]] ]
+; CHECK-NEXT:    ret i32 [[PHI2]]
+;
+  br i1 %c1, label %if1, label %else1
+
+if1:
+  br i1 %c2, label %if2, label %else2
+
+if2:
+  br label %j1 else2:
+  br label %j1
+
+else1:
+  br i1 %c3, label %j1, label %j2
+
+j1:
+  %phi1 = phi i32 [ 0, %if2 ], [ 1, %else2 ], [ 2, %else1 ]
+  br label %j2
+
+j2:
+  %phi2 = phi i32 [ %phi1, %j1 ], [ 3, %else1 ]
+  ret i32 %phi2
+}
+
+define i8 @merge1(i8 noundef %arg, i1 %c1, i1 %c2) {
+; CHECK-LABEL: define i8 @merge1
+; CHECK-SAME: (i8 noundef [[ARG:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 -123, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 66, label [[BB:%.*]]
+; CHECK-NEXT:    i8 123, label [[CASE2:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    [[C1_NOT:%.*]] = xor i1 [[C1]], true
+; CHECK-NEXT:    [[C2_NOT:%.*]] = xor i1 [[C2]], true
+; CHECK-NEXT:    [[BRMERGE:%.*]] = select i1 [[C1_NOT]], i1 true, i1 [[C2_NOT]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[C1_NOT]], i8 0, i8 3
+; CHECK-NEXT:    br i1 [[BRMERGE]], label [[BB]], label [[SUCC:%.*]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[BB]]
+; CHECK:       BB:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ [[DOTMUX]], [[CASE0]] ], [ 2, [[CASE2]] ], [ 1, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    br label [[SUCC]]
+; CHECK:       Succ:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[BB]] ], [ 4, [[CASE0]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+entry:
+  switch i8 %arg, label %unreachable [
+  i8 -123, label %case0
+  i8 66, label %case1
+  i8 123, label %case2
+  ]
+
+unreachable:
+  unreachable
+
+case0:
+  br i1 %c1, label %CommonPred, label %BB
+
+case1:
+  br label %BB
+
+case2:
+  br label %BB
+
+CommonPred:
+  br i1 %c2, label %Succ, label %BB
+
+BB:
+  %phi1 = phi i8 [ 0, %case0 ], [1, %case1],[2, %case2],[3,%CommonPred]
+  br label %Succ
+
+Succ:
+  %phi2 = phi i8 [ %phi1, %BB ], [ 4, %CommonPred ]
+  ret i8 %phi2
+}
+
+define i8 @merge1_unfoldable_one_block(i8 noundef %arg, i1 %c1, i1 %c2) {
+; CHECK-LABEL: define i8 @merge1_unfoldable_one_block
+; CHECK-SAME: (i8 noundef [[ARG:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 -123, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 66, label [[BB:%.*]]
+; CHECK-NEXT:    i8 123, label [[CASE2:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    [[C1_NOT:%.*]] = xor i1 [[C1]], true
+; CHECK-NEXT:    [[C2_NOT:%.*]] = xor i1 [[C2]], true
+; CHECK-NEXT:    [[BRMERGE:%.*]] = select i1 [[C1_NOT]], i1 true, i1 [[C2_NOT]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[C1_NOT]], i8 0, i8 3
+; CHECK-NEXT:    br i1 [[BRMERGE]], label [[BB]], label [[SUCC:%.*]]
+; CHECK:       case2:
+; CHECK-NEXT:    br label [[BB]]
+; CHECK:       BB:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ [[DOTMUX]], [[CASE0]] ], [ 2, [[CASE2]] ], [ 1, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    br label [[SUCC]]
+; CHECK:       Succ:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[BB]] ], [ 4, [[CASE0]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+entry:
+  switch i8 %arg, label %unreachable [
+  i8 -123, label %case0
+  i8 66, label %case1
+  i8 123, label %case2
+  ]
+
+unreachable:
+  unreachable
+
+case0:
+  call void @dummy()
+  br i1 %c1, label %CommonPred, label %BB
+
+case1:
+  br label %BB
+
+case2:
+  br label %BB
+
+CommonPred:
+  br i1 %c2, label %Succ, label %BB
+
+BB:
+  %phi1 = phi i8 [ 0, %case0 ], [1, %case1],[2, %case2],[3,%CommonPred]
+  br label %Succ
+
+Succ:
+  %phi2 = phi i8 [ %phi1, %BB ], [ 4, %CommonPred ]
+  ret i8 %phi2
+}
+
+define i8 @merge1_unfoldable_two_block(i8 noundef %arg, i1 %c1, i1 %c2) {
+; CHECK-LABEL: define i8 @merge1_unfoldable_two_block
+; CHECK-SAME: (i8 noundef [[ARG:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 -123, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 66, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 123, label [[BB:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    [[C1_NOT:%.*]] = xor i1 [[C1]], true
+; CHECK-NEXT:    [[C2_NOT:%.*]] = xor i1 [[C2]], true
+; CHECK-NEXT:    [[BRMERGE:%.*]] = select i1 [[C1_NOT]], i1 true, i1 [[C2_NOT]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[C1_NOT]], i8 0, i8 3
+; CHECK-NEXT:    br i1 [[BRMERGE]], label [[BB]], label [[SUCC:%.*]]
+; CHECK:       case1:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br label [[BB]]
+; CHECK:       BB:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ [[DOTMUX]], [[CASE0]] ], [ 1, [[CASE1]] ], [ 2, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    br label [[SUCC]]
+; CHECK:       Succ:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[BB]] ], [ 4, [[CASE0]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+entry:
+  switch i8 %arg, label %unreachable [
+  i8 -123, label %case0
+  i8 66, label %case1
+  i8 123, label %case2
+  ]
+
+unreachable:
+  unreachable
+
+case0:
+call void @dummy()
+  br i1 %c1, label %CommonPred, label %BB
+
+case1:
+call void @dummy()
+  br label %BB
+
+case2:
+  br label %BB
+
+CommonPred:
+  br i1 %c2, label %Succ, label %BB
+
+BB:
+  %phi1 = phi i8 [ 0, %case0 ], [1, %case1],[2, %case2],[3,%CommonPred]
+  br label %Succ
+
+Succ:
+  %phi2 = phi i8 [ %phi1, %BB ], [ 4, %CommonPred ]
+  ret i8 %phi2
+}
+
+define i8 @merge1_unfoldable_all_block(i8 noundef %arg, i1 %c1, i1 %c2) {
+; CHECK-LABEL: define i8 @merge1_unfoldable_all_block
+; CHECK-SAME: (i8 noundef [[ARG:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i8 [[ARG]], label [[UNREACHABLE:%.*]] [
+; CHECK-NEXT:    i8 -123, label [[CASE0:%.*]]
+; CHECK-NEXT:    i8 66, label [[CASE1:%.*]]
+; CHECK-NEXT:    i8 123, label [[CASE2:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       unreachable:
+; CHECK-NEXT:    unreachable
+; CHECK:       case0:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br i1 [[C1]], label [[COMMONPRED:%.*]], label [[BB:%.*]]
+; CHECK:       case1:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br label [[BB]]
+; CHECK:       case2:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br label [[BB]]
+; CHECK:       CommonPred:
+; CHECK-NEXT:    call void @dummy()
+; CHECK-NEXT:    br i1 [[C2]], label [[SUCC:%.*]], label [[BB]]
+; CHECK:       BB:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i8 [ 0, [[CASE0]] ], [ 1, [[CASE1]] ], [ 2, [[CASE2]] ], [ 3, [[COMMONPRED]] ]
+; CHECK-NEXT:    br label [[SUCC]]
+; CHECK:       Succ:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi i8 [ [[PHI1]], [[BB]] ], [ 4, [[COMMONPRED]] ]
+; CHECK-NEXT:    ret i8 [[PHI2]]
+;
+entry:
+  switch i8 %arg, label %unreachable [
+  i8 -123, label %case0
+  i8 66, label %case1
+  i8 123, label %case2
+  ]
+
+unreachable:
+  unreachable
+
+case0:
+call void @dummy()
+  br i1 %c1, label %CommonPred, label %BB
+
+case1:
+call void @dummy()
+  br label %BB
+
+case2:
+call void @dummy()
+  br label %BB
+
+CommonPred:
+call void @dummy()
+  br i1 %c2, label %Succ, label %BB
+
+BB:
+  %phi1 = phi i8 [ 0, %case0 ], [1, %case1],[2, %case2],[3,%CommonPred]
+  br label %Succ
+
+Succ:
+  %phi2 = phi i8 [ %phi1, %BB ], [ 4, %CommonPred ]
+  ret i8 %phi2
+}
+
+declare void @dummy()
+