diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4640,7 +4640,8 @@
   if (auto *CondC = dyn_cast<Constant>(Cond)) {
     if (auto *TrueC = dyn_cast<Constant>(TrueVal))
       if (auto *FalseC = dyn_cast<Constant>(FalseVal))
-        return ConstantFoldSelectInstruction(CondC, TrueC, FalseC);
+        if (Constant *C = ConstantFoldSelectInstruction(CondC, TrueC, FalseC))
+          return C;
 
     // select poison, X, Y -> poison
     if (isa<PoisonValue>(CondC))
diff --git a/llvm/test/Transforms/InstSimplify/select-inseltpoison.ll b/llvm/test/Transforms/InstSimplify/select-inseltpoison.ll
--- a/llvm/test/Transforms/InstSimplify/select-inseltpoison.ll
+++ b/llvm/test/Transforms/InstSimplify/select-inseltpoison.ll
@@ -881,11 +881,19 @@
   ret <2 x float> %s
 }
 
-; Negative tests. Don't fold if the non-undef operand is a constexpr.
+@a = external global [3 x ptr]
+define i32 @all_constant_false_undef_true_poison_gen_constexpr(i1 %a) {
+; CHECK-LABEL: @all_constant_false_undef_true_poison_gen_constexpr(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[A:%.*]], i32 ptrtoint (ptr getelementptr inbounds ([3 x ptr], ptr @a, i64 2) to i32), i32 undef
+; CHECK-NEXT:    ret i32 [[S]]
+;
+  %s = select i1 %a, i32 ptrtoint (ptr getelementptr inbounds ([3 x ptr], ptr @a, i64 2) to i32), i32 undef
+  ret i32 %s
+}
+
 define i32 @all_constant_false_undef_true_constexpr() {
 ; CHECK-LABEL: @all_constant_false_undef_true_constexpr(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32), i32 undef
-; CHECK-NEXT:    ret i32 [[S]]
+; CHECK-NEXT:    ret i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32)
 ;
   %s = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32), i32 undef
   ret i32 %s
@@ -893,8 +901,7 @@
 
 define i32 @all_constant_true_undef_false_constexpr() {
 ; CHECK-LABEL: @all_constant_true_undef_false_constexpr(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
-; CHECK-NEXT:    ret i32 [[S]]
+; CHECK-NEXT:    ret i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
 ;
   %s = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
   ret i32 %s
@@ -903,8 +910,7 @@
 ; Negative tests. Don't fold if the non-undef operand is a vector containing a constexpr.
 define <2 x i32> @all_constant_false_undef_true_constexpr_vec() {
 ; CHECK-LABEL: @all_constant_false_undef_true_constexpr_vec(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
-; CHECK-NEXT:    ret <2 x i32> [[S]]
+; CHECK-NEXT:    ret <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>
 ;
   %s = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
   ret <2 x i32> %s
@@ -912,8 +918,7 @@
 
 define <2 x i32> @all_constant_true_undef_false_constexpr_vec() {
 ; CHECK-LABEL: @all_constant_true_undef_false_constexpr_vec(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32> <i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
-; CHECK-NEXT:    ret <2 x i32> [[S]]
+; CHECK-NEXT:    ret <2 x i32> <i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
 ;
   %s = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32><i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
   ret <2 x i32> %s
diff --git a/llvm/test/Transforms/InstSimplify/select.ll b/llvm/test/Transforms/InstSimplify/select.ll
--- a/llvm/test/Transforms/InstSimplify/select.ll
+++ b/llvm/test/Transforms/InstSimplify/select.ll
@@ -9,6 +9,14 @@
   ret i1 %s
 }
 
+define i1 @cond_constexpr_bool_true_or_false(i1 %cond) {
+; CHECK-LABEL: @cond_constexpr_bool_true_or_false(
+; CHECK-NEXT:    ret i1 ptrtoint (ptr @cond_constexpr_bool_true_or_false to i1)
+;
+  %s = select i1 ptrtoint (ptr @cond_constexpr_bool_true_or_false to i1), i1 true, i1 false
+  ret i1 %s
+}
+
 define <2 x i1> @bool_true_or_false_vec(<2 x i1> %cond) {
 ; CHECK-LABEL: @bool_true_or_false_vec(
 ; CHECK-NEXT:    ret <2 x i1> [[COND:%.*]]
@@ -884,8 +892,7 @@
 ; Negative tests. Don't fold if the non-undef operand is a constexpr.
 define i32 @all_constant_false_undef_true_constexpr() {
 ; CHECK-LABEL: @all_constant_false_undef_true_constexpr(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32), i32 undef
-; CHECK-NEXT:    ret i32 [[S]]
+; CHECK-NEXT:    ret i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32)
 ;
   %s = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr to i32), i32 undef
   ret i32 %s
@@ -893,8 +900,7 @@
 
 define i32 @all_constant_true_undef_false_constexpr() {
 ; CHECK-LABEL: @all_constant_true_undef_false_constexpr(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
-; CHECK-NEXT:    ret i32 [[S]]
+; CHECK-NEXT:    ret i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
 ;
   %s = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr to i32)
   ret i32 %s
@@ -903,8 +909,7 @@
 ; Negative tests. Don't fold if the non-undef operand is a vector containing a constexpr.
 define <2 x i32> @all_constant_false_undef_true_constexpr_vec() {
 ; CHECK-LABEL: @all_constant_false_undef_true_constexpr_vec(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
-; CHECK-NEXT:    ret <2 x i32> [[S]]
+; CHECK-NEXT:    ret <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>
 ;
   %s = select i1 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (ptr @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
   ret <2 x i32> %s
@@ -912,8 +917,7 @@
 
 define <2 x i32> @all_constant_true_undef_false_constexpr_vec() {
 ; CHECK-LABEL: @all_constant_true_undef_false_constexpr_vec(
-; CHECK-NEXT:    [[S:%.*]] = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32> <i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
-; CHECK-NEXT:    ret <2 x i32> [[S]]
+; CHECK-NEXT:    ret <2 x i32> <i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
 ;
   %s = select i1 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32><i32 -1, i32 ptrtoint (ptr @all_constant_true_undef_false_constexpr_vec to i32)>
   ret <2 x i32> %s