Merge pull request MicrosoftDocs#167 from manbearian/patch-1

Remove __declspec(noalias) from example

Author: Colin Robertson

docs/cpp/restrict.md

@@ -1,7 +1,7 @@
 ---
 title: "restrict | Microsoft Docs"
 ms.custom: ""
-ms.date: "11/04/2016"
+ms.date: "02/09/2018"
 ms.reviewer: ""
 ms.suite: ""
 ms.technology: ["cpp-language"]
@@ -18,30 +18,104 @@ manager: "ghogen"
 ms.workload: ["cplusplus"]
 ---
 # restrict
-**Microsoft Specific**  
+
+**Microsoft Specific**
+
+When applied to a function declaration or definition that returns a pointer type, `restrict` tells the compiler that the function returns an object that is not *aliased*, that is, referenced by any other pointers. This allows the compiler to perform additional optimizations.
+
+## Syntax
+
+> **__declspec(restrict)** *pointer_return_type* *function*();  
   
- Applied to a function declaration or definition that returns a pointer type and tells the compiler that the function returns an object that will not be aliased with any other pointers.  
+## Remarks
+
+The compiler propagates `__declspec(restrict)`. For example, the CRT `malloc` function has a `__declspec(restrict)` decoration, and therefore, the compiler assumes that pointers initialized to memory locations by `malloc` are also not aliased by previously existing pointers.
+
+The compiler does not check that the returned pointer is not actually aliased. It is the developer's responsibility to ensure the program does not alias a pointer marked with the `restrict __declspec` modifier.  
 
-## Syntax  
-  
-```  
-__declspec(restrict) return_type f();  
-```  
-  
-## Remarks  
- The compiler will propagate `__declspec(restrict)`. For example, the CRT `malloc` function is decorated with `__declspec(restrict)` and therefore, pointers initialized to memory locations with `malloc` are also implied to not be aliased.  
-  
- The compiler does not check that the pointer is actually not aliased. It is the developer's responsibility to ensure the program does not alias a pointer marked with the `restrict __declspec` modifier.  
-  
- For similar semantics on variables, see [__restrict](../cpp/extension-restrict.md).  
+For similar semantics on variables, see [__restrict](../cpp/extension-restrict.md).
+ 
+For another annotation that applies to aliasing within a function, see [__declspec(noalias)](../cpp/noalias.md).
 
+For information about the **restrict** keyword that is part of C++ AMP, see [restrict (C++ AMP)](../cpp/restrict-cpp-amp.md).  
+ 
 ## Example  
- See [noalias](../cpp/noalias.md) for an example using `restrict`.  
-  
- For information about the restrict keyword that is part of C++ AMP, see [restrict (C++ AMP)](../cpp/restrict-cpp-amp.md).  
-  
- **END Microsoft Specific**  
-  
-## See Also  
- [__declspec](../cpp/declspec.md)   
- [Keywords](../cpp/keywords-cpp.md)
+
+The following sample demonstrates the use of `__declspec(restrict)`.
+
+When `__declspec(restrict)` is applied to a function that returns a pointer, this tells the compiler that the memory pointed to by the return value is not aliased. In this example, the pointers `mempool` and `memptr` are global, so the compiler can't be sure that the memory they refer to is not aliased. However, they are used within `ma` and its caller `init` in a way that returns memory that isn't otherwise referenced by the program, so `__decslpec(restrict)` is used to help the optimizer. This is similar to how the CRT headers decorate allocation functions such as `malloc` by using `__declspec(restrict)` to indicate that they always return memory that cannot be aliased by existing pointers.
+
+```C
+// declspec_restrict.c
+// Compile with: cl /W4 declspec_restrict.c
+#include <stdio.h>
+#include <stdlib.h>
+
+#define M 800
+#define N 600
+#define P 700
+
+float * mempool, * memptr;
+
+__declspec(restrict) float * ma(int size)
+{
+    float * retval;
+    retval = memptr;
+    memptr += size;
+    return retval;
+}
+
+__declspec(restrict) float * init(int m, int n)
+{
+    float * a;
+    int i, j;
+    int k=1;
+
+    a = ma(m * n);
+    if (!a) exit(1);
+    for (i=0; i<m; i++)
+        for (j=0; j<n; j++)
+            a[i*n+j] = 0.1f/k++;
+    return a;
+}
+
+void multiply(float * a, float * b, float * c)
+{
+    int i, j, k;
+
+    for (j=0; j<P; j++)
+        for (i=0; i<M; i++)
+            for (k=0; k<N; k++)
+                c[i * P + j] =
+                          a[i * N + k] *
+                          b[k * P + j];
+}
+
+int main()
+{
+    float * a, * b, * c;
+
+    mempool = (float *) malloc(sizeof(float) * (M*N + N*P + M*P));
+
+    if (!mempool)
+    {
+        puts("ERROR: Malloc returned null");
+        exit(1);
+    }
+
+    memptr = mempool;
+    a = init(M, N);
+    b = init(N, P);
+    c = init(M, P);
+
+    multiply(a, b, c);
+}
+```
+
+**END Microsoft Specific**
+
+## See also
+
+[Keywords](../cpp/keywords-cpp.md)  
+[__declspec](../cpp/declspec.md)  
+[__declspec(noalias)](../cpp/noalias.md)