diff --git a/llvm/include/llvm/Analysis/TargetLibraryInfo.h b/llvm/include/llvm/Analysis/TargetLibraryInfo.h
--- a/llvm/include/llvm/Analysis/TargetLibraryInfo.h
+++ b/llvm/include/llvm/Analysis/TargetLibraryInfo.h
@@ -76,7 +76,7 @@
   /// Return true if the function type FTy is valid for the library function
   /// F, regardless of whether the function is available.
   bool isValidProtoForLibFunc(const FunctionType &FTy, LibFunc F,
-                              const DataLayout &DL) const;
+                              const Module &M) const;
 
 public:
   /// List of known vector-functions libraries.
@@ -192,6 +192,9 @@
   /// This queries the 'wchar_size' metadata.
   unsigned getWCharSize(const Module &M) const;
 
+  /// Returns the size of the size_t type in bits or 0 if the size is unknown.
+  unsigned getSizeTSize(const Module &M) const;
+
   /// Get size of a C-level int or unsigned int, in bits.
   unsigned getIntSize() const {
     return SizeOfInt;
@@ -403,6 +406,11 @@
     return Impl->getWCharSize(M);
   }
 
+  /// \copydoc TargetLibraryInfoImpl::getSizeTSize()
+  unsigned getSizeTSize(const Module &M) const {
+    return Impl->getSizeTSize(M);
+  }
+
   /// \copydoc TargetLibraryInfoImpl::getIntSize()
   unsigned getIntSize() const {
     return Impl->getIntSize();
diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -727,15 +727,8 @@
 
 bool TargetLibraryInfoImpl::isValidProtoForLibFunc(const FunctionType &FTy,
                                                    LibFunc F,
-                                                   const DataLayout &DL) const {
-  LLVMContext &Ctx = FTy.getContext();
-  // FIXME: There is really no guarantee that sizeof(size_t) is equal to
-  // sizeof(int*) for every target. So the assumption used here to derive the
-  // SizeTTy based on DataLayout and getIntPtrType isn't always valid.
-  Type *SizeTTy = DL.getIntPtrType(Ctx, /*AddressSpace=*/0);
-  auto IsSizeTTy = [SizeTTy](Type *Ty) {
-    return Ty == SizeTTy;
-  };
+                                                   const Module &M) const {
+  unsigned SizeTBits = getSizeTSize(M);
   unsigned NumParams = FTy.getNumParams();
 
   switch (F) {
@@ -759,12 +752,12 @@
             FTy.getReturnType()->isIntegerTy(32));
   case LibFunc_strlen_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strlen:
     return NumParams == 1 && FTy.getParamType(0)->isPointerTy() &&
-           IsSizeTTy(FTy.getReturnType());
+           FTy.getReturnType()->isIntegerTy(SizeTBits);
 
   case LibFunc_strchr:
   case LibFunc_strrchr:
@@ -784,7 +777,7 @@
             FTy.getParamType(1)->isPointerTy());
   case LibFunc_strcat_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strcat:
@@ -794,19 +787,19 @@
 
   case LibFunc_strncat_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strncat:
     return (NumParams == 3 && FTy.getReturnType()->isPointerTy() &&
             FTy.getParamType(0) == FTy.getReturnType() &&
             FTy.getParamType(1) == FTy.getReturnType() &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_strcpy_chk:
   case LibFunc_stpcpy_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strcpy:
@@ -818,20 +811,20 @@
   case LibFunc_strlcat_chk:
   case LibFunc_strlcpy_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strlcat:
   case LibFunc_strlcpy:
-    return NumParams == 3 && IsSizeTTy(FTy.getReturnType()) &&
+    return NumParams == 3 && FTy.getReturnType()->isIntegerTy(SizeTBits) &&
            FTy.getParamType(0)->isPointerTy() &&
            FTy.getParamType(1)->isPointerTy() &&
-           IsSizeTTy(FTy.getParamType(2));
+           FTy.getParamType(2)->isIntegerTy(SizeTBits);
 
   case LibFunc_strncpy_chk:
   case LibFunc_stpncpy_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_strncpy:
@@ -839,7 +832,7 @@
     return (NumParams == 3 && FTy.getReturnType() == FTy.getParamType(0) &&
             FTy.getParamType(0) == FTy.getParamType(1) &&
             FTy.getParamType(0)->isPointerTy() &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_strxfrm:
     return (NumParams == 3 && FTy.getParamType(0)->isPointerTy() &&
@@ -854,7 +847,7 @@
     return (NumParams == 3 && FTy.getReturnType()->isIntegerTy(32) &&
             FTy.getParamType(0)->isPointerTy() &&
             FTy.getParamType(0) == FTy.getParamType(1) &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_strspn:
   case LibFunc_strcspn:
@@ -902,21 +895,21 @@
   case LibFunc_sprintf_chk:
     return NumParams == 4 && FTy.getParamType(0)->isPointerTy() &&
            FTy.getParamType(1)->isIntegerTy(32) &&
-           IsSizeTTy(FTy.getParamType(2)) &&
+           FTy.getParamType(2)->isIntegerTy(SizeTBits) &&
            FTy.getParamType(3)->isPointerTy() &&
            FTy.getReturnType()->isIntegerTy(32);
 
   case LibFunc_snprintf:
     return NumParams == 3 && FTy.getParamType(0)->isPointerTy() &&
-           IsSizeTTy(FTy.getParamType(1)) &&
+           FTy.getParamType(1)->isIntegerTy(SizeTBits) &&
            FTy.getParamType(2)->isPointerTy() &&
            FTy.getReturnType()->isIntegerTy(32);
 
   case LibFunc_snprintf_chk:
     return NumParams == 5 && FTy.getParamType(0)->isPointerTy() &&
-           IsSizeTTy(FTy.getParamType(1)) &&
+           FTy.getParamType(1)->isIntegerTy(SizeTBits) &&
            FTy.getParamType(2)->isIntegerTy(32) &&
-           IsSizeTTy(FTy.getParamType(3)) &&
+           FTy.getParamType(3)->isIntegerTy(SizeTBits) &&
            FTy.getParamType(4)->isPointerTy() &&
            FTy.getReturnType()->isIntegerTy(32);
 
@@ -932,14 +925,15 @@
   case LibFunc_memcmp:
     return NumParams == 3 && FTy.getReturnType()->isIntegerTy(32) &&
            FTy.getParamType(0)->isPointerTy() &&
-           FTy.getParamType(1)->isPointerTy() && IsSizeTTy(FTy.getParamType(2));
+           FTy.getParamType(1)->isPointerTy() &&
+           FTy.getParamType(2)->isIntegerTy(SizeTBits);
 
   case LibFunc_memchr:
   case LibFunc_memrchr:
     return (NumParams == 3 && FTy.getReturnType()->isPointerTy() &&
             FTy.getReturnType() == FTy.getParamType(0) &&
             FTy.getParamType(1)->isIntegerTy(32) &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
   case LibFunc_modf:
   case LibFunc_modff:
   case LibFunc_modfl:
@@ -949,7 +943,7 @@
   case LibFunc_mempcpy_chk:
   case LibFunc_memmove_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_memcpy:
@@ -958,22 +952,22 @@
     return (NumParams == 3 && FTy.getReturnType() == FTy.getParamType(0) &&
             FTy.getParamType(0)->isPointerTy() &&
             FTy.getParamType(1)->isPointerTy() &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_memset_chk:
     --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_memset:
     return (NumParams == 3 && FTy.getReturnType() == FTy.getParamType(0) &&
             FTy.getParamType(0)->isPointerTy() &&
             FTy.getParamType(1)->isIntegerTy() &&
-            IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_memccpy_chk:
       --NumParams;
-    if (!IsSizeTTy(FTy.getParamType(NumParams)))
+    if (!FTy.getParamType(NumParams)->isIntegerTy(SizeTBits))
       return false;
     LLVM_FALLTHROUGH;
   case LibFunc_memccpy:
@@ -985,7 +979,7 @@
   case LibFunc_vec_realloc:
     return (NumParams == 2 && FTy.getReturnType()->isPointerTy() &&
             FTy.getParamType(0) == FTy.getReturnType() &&
-            IsSizeTTy(FTy.getParamType(1)));
+            FTy.getParamType(1)->isIntegerTy(SizeTBits));
   case LibFunc_read:
     return (NumParams == 3 && FTy.getParamType(1)->isPointerTy());
   case LibFunc_rewind:
@@ -1066,7 +1060,7 @@
     return (NumParams != 0 && FTy.getParamType(0)->isPointerTy());
   case LibFunc___kmpc_free_shared:
     return (NumParams == 2 && FTy.getParamType(0)->isPointerTy() &&
-            IsSizeTTy(FTy.getParamType(1)));
+            FTy.getParamType(1)->isIntegerTy(SizeTBits));
 
   case LibFunc_fopen:
     return (NumParams == 2 && FTy.getReturnType()->isPointerTy() &&
@@ -1156,14 +1150,14 @@
   case LibFunc_vsprintf_chk:
     return NumParams == 5 && FTy.getParamType(0)->isPointerTy() &&
            FTy.getParamType(1)->isIntegerTy(32) &&
-           IsSizeTTy(FTy.getParamType(2)) && FTy.getParamType(3)->isPointerTy();
+           FTy.getParamType(2)->isIntegerTy(SizeTBits) && FTy.getParamType(3)->isPointerTy();
   case LibFunc_vsnprintf:
     return (NumParams == 4 && FTy.getParamType(0)->isPointerTy() &&
             FTy.getParamType(2)->isPointerTy());
   case LibFunc_vsnprintf_chk:
     return NumParams == 6 && FTy.getParamType(0)->isPointerTy() &&
            FTy.getParamType(2)->isIntegerTy(32) &&
-           IsSizeTTy(FTy.getParamType(3)) && FTy.getParamType(4)->isPointerTy();
+           FTy.getParamType(3)->isIntegerTy(SizeTBits) && FTy.getParamType(4)->isPointerTy();
   case LibFunc_open:
     return (NumParams >= 2 && FTy.getParamType(0)->isPointerTy());
   case LibFunc_opendir:
@@ -1575,12 +1569,13 @@
   case LibFunc_strnlen:
     return (NumParams == 2 && FTy.getReturnType() == FTy.getParamType(1) &&
             FTy.getParamType(0)->isPointerTy() &&
-            IsSizeTTy(FTy.getParamType(1)));
+            FTy.getParamType(1)->isIntegerTy(SizeTBits));
 
   case LibFunc_posix_memalign:
     return (NumParams == 3 && FTy.getReturnType()->isIntegerTy(32) &&
             FTy.getParamType(0)->isPointerTy() &&
-            IsSizeTTy(FTy.getParamType(1)) && IsSizeTTy(FTy.getParamType(2)));
+            FTy.getParamType(1)->isIntegerTy(SizeTBits) &&
+            FTy.getParamType(2)->isIntegerTy(SizeTBits));
 
   case LibFunc_wcslen:
     return (NumParams == 1 && FTy.getParamType(0)->isPointerTy() &&
@@ -1624,7 +1619,7 @@
   assert(M && "Expecting FDecl to be connected to a Module.");
 
   return getLibFunc(FDecl.getName(), F) &&
-         isValidProtoForLibFunc(*FDecl.getFunctionType(), F, M->getDataLayout());
+         isValidProtoForLibFunc(*FDecl.getFunctionType(), F, *M);
 }
 
 void TargetLibraryInfoImpl::disableAllFunctions() {
@@ -1740,6 +1735,18 @@
   return 0;
 }
 
+unsigned TargetLibraryInfoImpl::getSizeTSize(const Module &M) const {
+  // There is really no guarantee that sizeof(size_t) is equal to sizeof(int*)
+  // for every target. If that isn't true then it should be possible to derive
+  // the SizeTTy from the target tripe here instead and do an early return.
+
+  // Here we assume that sizeof(size_t) is equal to sizeof(int*) in address
+  // space zero. This should work for most targets.
+  // TODO: Should this use getIndexSizeInBits instead?
+  const DataLayout &DL = M.getDataLayout();
+  return DL.getPointerSizeInBits(/*AddressSpace=*/0);
+}
+
 TargetLibraryInfoWrapperPass::TargetLibraryInfoWrapperPass()
     : ImmutablePass(ID), TLA(TargetLibraryInfoImpl()) {
   initializeTargetLibraryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -3295,7 +3295,8 @@
   else
     return nullptr;
 
-  Type *SizeTTy = DL.getIntPtrType(CI->getContext());
+  unsigned SizeTBits = TLI->getSizeTSize(*CI->getModule());
+  Type *SizeTTy = IntegerType::get(CI->getContext(), SizeTBits);
   Value *LenV = ConstantInt::get(SizeTTy, Len);
   Value *Ret = emitMemCpyChk(Dst, Src, LenV, ObjSize, B, DL, TLI);
   // If the function was an __stpcpy_chk, and we were able to fold it into