Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -563,6 +563,52 @@
     return B.CreateZExt(B.CreateLoad(B.getInt8Ty(), Str1P, "strcmpload"),
                         CI->getType());
 
+  // Fold strcmp(P, "x"), strcmp(P, "xx")
+  if (HasStr2 && (Str2.size() == 1 || Str2.size() == 2)) {
+    if (Str2.size() == 2) {
+      return nullptr;
+    }
+
+    BasicBlock *InsertBB = B.GetInsertBlock();
+
+    /// Split basic block before and after strcmp call
+    BasicBlock *JoinBB = InsertBB->splitBasicBlock(CI, "strcmp_fold_sub_join");
+
+    // Erase br instruction
+    InsertBB->erase(--InsertBB->end(), InsertBB->end());
+
+    B.SetInsertPoint(InsertBB);
+    Value *Str1FirstCharacterValue = B.CreateIntCast(
+        B.CreateLoad(B.getInt8Ty(), Str1P), B.getInt32Ty(), true);
+    Value *Str2FirstCharacterValue = ConstantInt::get(
+        B.getInt32Ty(), static_cast<unsigned char>(Str2[0]), true);
+    Value *FirstCharacterSub =
+        B.CreateNSWSub(Str1FirstCharacterValue, Str2FirstCharacterValue);
+
+    BasicBlock *SubIsZeroBB =
+        BasicBlock::Create(B.getContext(), "strcmp_fold_sub_is_zero",
+                           InsertBB->getParent(), JoinBB);
+    B.CreateCondBr(B.CreateICmpEQ(FirstCharacterSub,
+                                  ConstantInt::get(B.getInt32Ty(), 0, true)),
+                   SubIsZeroBB, JoinBB);
+
+    B.SetInsertPoint(SubIsZeroBB);
+    Value *Str1SecondCharacterValue = B.CreateIntCast(
+        B.CreateLoad(B.getInt8Ty(),
+                     B.CreateConstInBoundsGEP1_32(B.getInt8Ty(), Str1P, 1)),
+        B.getInt32Ty(), true);
+    B.CreateBr(JoinBB);
+
+    B.SetInsertPoint(JoinBB);
+
+    /// Insert PHI in join block before strcmp call
+    PHINode *Result = PHINode::Create(B.getInt32Ty(), 2, "", CI);
+    Result->addIncoming(FirstCharacterSub, InsertBB);
+    Result->addIncoming(Str1SecondCharacterValue, SubIsZeroBB);
+
+    return Result;
+  }
+
   // strcmp(P, "x") -> memcmp(P, "x", 2)
   uint64_t Len1 = GetStringLength(Str1P);
   if (Len1)
Index: llvm/test/Transforms/InstCombine/strcmp-5.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/strcmp-5.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; TODO: Test that ...
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare i32 @strcmp(ptr, ptr)
+
+@s1 = constant [2 x i8] c"0\00"
+@s2 = constant [3 x i8] c"05\00"
+
+; Fold strcmp(C, "x"), strcmp(C, "xx").
+
+define i1 @fold_strcmp_s1_1(ptr %C) {
+; CHECK-LABEL: @fold_strcmp_s1_1(
+; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr %C, align 1
+; CHECK-NEXT:    [[SEXT1:%.*]] = sext i8 [[TMP1]] to i32
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[SEXT1]], -48
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 [[ADD]], 0
+; CHECK-NEXT:    br i1 [[CMP1]], label %strcmp_fold_sub_is_zero, label %strcmp_fold_sub_join
+; CHECK-LABEL: strcmp_fold_sub_is_zero:
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, ptr %C, i64 1
+; CHECK-NEXT:    [[TMP3:%.*]] = load i8, ptr [[TMP2]], align 1
+; CHECK-NEXT:    [[SEXT2:%.*]] = sext i8 [[TMP3]] to i32
+; CHECK-NEXT:    br label %strcmp_fold_sub_join
+; CHECK-LABEL: strcmp_fold_sub_join:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ [[ADD]], %0 ], [ [[SEXT2]], %strcmp_fold_sub_is_zero ]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[PHI]], 0
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %call = call i32 @strcmp(ptr %C, ptr noundef @s1)
+  %cmp = icmp eq i32 %call, 0
+  ret i1 %cmp
+}
+
+define i32 @fold_strcmp_s1_2(ptr %C) {
+; CHECK-LABEL: @fold_strcmp_s1_2(
+; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr %C, align 1
+; CHECK-NEXT:    [[SEXT1:%.*]] = sext i8 [[TMP1]] to i32
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[SEXT1]], -48
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 [[ADD]], 0
+; CHECK-NEXT:    br i1 [[CMP1]], label %strcmp_fold_sub_is_zero, label %strcmp_fold_sub_join
+; CHECK-LABEL: strcmp_fold_sub_is_zero:
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, ptr %C, i64 1
+; CHECK-NEXT:    [[TMP3:%.*]] = load i8, ptr [[TMP2]], align 1
+; CHECK-NEXT:    [[SEXT2:%.*]] = sext i8 [[TMP3]] to i32
+; CHECK-NEXT:    br label %strcmp_fold_sub_join
+; CHECK-LABEL: strcmp_fold_sub_join:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ [[ADD]], %0 ], [ [[SEXT2]], %strcmp_fold_sub_is_zero ]
+; CHECK-NEXT:    ret i32 [[PHI]]
+;
+  %call = call i32 @strcmp(ptr %C, ptr noundef @s1)
+  ret i32 %call
+}