矢量化程序和并行化程序消息

  • 项目

你可以使用 Visual C++ 编译器选项 /Qpar-report 和 /Qvec-report 来设置自动并行化错误和警告以输出原因代码及有关其活动的信息性消息。 本文说明原因代码和消息。

  • 信息性消息 5001 至 5021

  • 原因代码 500 至 504

  • 原因代码 1000 至 1009

  • 原因代码 1100 至 1106

  • 原因代码 1200 至 1203

  • 原因代码 1300 至 1305

  • 原因代码 1400 至 1405

  • 原因代码 1500 至 1505

信息性消息

根据你指定的报告级别，将为每个循环显示下列信息性消息之一。

有关原因代码的信息，请参见本文的下一部分。

信息性消息

说明

5001

循环已向量化。

5002

由于原因“description”，循环未向量化。

5011

循环已并行化。

5012

由于原因“description”，循环未并行化。

5021

无法将循环与杂注关联。

原因代码

以下几节列出了自动并行化和自动向量化的可能原因代码。

50x

50x 原因代码应用于自动并行化和自动向量化。

原因代码

说明

500

这是包含多个用例的泛型消息（例如，该循环包含多个退出，或循环标头不会因增加归纳变量而结束）。

501

归纳变量不是本地的；或上限绑定不是循环固定的。

502

除了简单 +1 外，归纳变量以某种方式单步执行。

503

循环包含异常处理或 switch 语句。

504

循环体可能会引发需要析构 C++ 对象的异常。

 
void code_500(int *A)
{
    // Code 500 is emitted if the loop has non-vectorizable flow.
    // This can include "if", "break", "continue", the conditional 
    // operator "?", or function calls.
    // It also encompasses correct definition and use of the induction
    // variable "i", in that the increment "++i" or "i++" must be the last
    // statement in the loop.

    int i = 0;
    while (i<1000)
    {
        if (i == 4) 
        {
            break;
        }

        ++i;

        A[i] = A[i] + 1;
    }
    // To resolve code 500, use a 'for' loop with single increment of 
    // induction variable.

    for (int i=0; i<1000; ++i)
    {       
        A[i] = A[i] + 1;
    }    
}

int bound();
void code_501_example1(int *A)
{
    // Code 501 is emitted if the compiler cannot discern the
    // induction variable of this loop. In this case, when it checks
    // the upperbound of 'i', the compiler cannot prove that the 
    // function call "bound()" returns the same value each time.
    // Also, the compiler cannot prove that the call to "bound()"
    // does not modify the values of array A.

    for (int i=0; i<bound(); ++i)
    {
        A[i] = A[i] + 1;
    }

    // To resolve code 501, ensure that the induction variable is 
    // a local variable, and ensure that the upperbound is a
    // provably loop invariant value.

    for (int i=0, imax = bound(); i<imax; ++i)
    {
        A[i] = A[i] + 1;
    }
}

int i;
void code_501_example2(int *A)
{
    // Code 501 is emitted if the compiler cannot discern the
    // induction variable of this loop. In this case, 'i' is
    // a global.

    for (i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }

    // To resolve code 501, ensure that the induction variable is 
    // a local variable, and ensure that the upperbound is a
    // provably loop invariant value.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

void code_502(int *A)
{
    // Code 502 is emitted if the compiler cannot discern
    // the induction variable of the loop. In this case,
    // there are three increments to "i", one of which
    // is conditional.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
        ++i;

        if (i < 100) 
        {
            ++i;
        }
    }

    // To resolve code 502, ensure that there is just one 
    // increment of the induction variable, placed in the usual
    // spot in the "for" loop.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

void code_503(int *A, int x)
{
    // Code 503 is emitted if there are inadmissible
    // operations in the loop - for example, exception handling and
    // switch statements.

    for (int i = 0; i<1000; ++i)
    {
        switch (x)
        {
        case 1: A[i] = A[i] + 1;
        case 2: A[i] = A[i] + 2;
        case 3: A[i] = A[i] + 3;
            break;
        }
    }

    // To resolve code 503, try to remove as many switch statements
    // and exception handling constructs as possible.
}

// compile with /EHsc

int code_504_helper();
class C504
{
public:
    C504();
    ~C504();
};

void code_504(int *A) {
    // Code 504 is emitted if a C++ object was created and
    // that object requires EH unwind tracking information under
    // /EHs or /EHsc.

    for(int i = 0; i < 1000; ++i)
    {
        C504 c;
        A[i] = code_504_helper();
    }

}

100x

100x 原因代码应用于自动并行化。

原因代码

说明

1000

编译器在循环体中检测到数据依赖项。

1001

编译器在循环体中检测到标量变量的存储，该标量在循环外使用。

1002

编译器尝试实现具有已并行化的内部循环的循环的并行化。

1003

循环体包含可读取或写入内存的内部调用。

1004

循环体中的标量降低。 如果循环已向量化，标量会减少。

1005

已指定 no_parallel 杂注。

1006

该函数包含 openmp。 通过移除此函数中的所有 openmp 解决此问题。

1007

循环归纳变量或循环绑定不是有符号的 32 位数字（int 或 long）。 通过更改归纳变量的类型解决此问题。

1008

编译器检测到此循环未执行足够的工作来保证自动并行化。

1009

编译器检测到并行化“do-while”循环的尝试。 自动并行化只针对 for 循环。

 
int A[1000];
void func();
void code_1000()
{
    // Code 1000 is emitted if the compiler detects a 
    // data dependence in the loop body. 

    // You can resolve this by using the ivdep pragma.
    // CAUTION -- the compiler will trust your
    // assertion that there are no data dependencies
    // in the loop body. If there are, you are generating
    // code that may have race conditions.

#pragma loop(hint_parallel(0))
    //#pragma loop(ivdep) // ivdep will force this through.
    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i-1] + 1;  // data dependence here
        func();             // data dependence here
    }
}

int code_1001()
{
    // Code 1001 is emitted if the compiler detects
    // a store to a scalar variable in the loop
    // body, and that scalar has a use beyond the loop.

    // Resolve this by rewriting your code so
    // that the scalar is not needed.

    int s = 0;
#pragma loop(hint_parallel(0))
    for (int i=0; i<1000; ++i)
    {
        s = A[i];
    }
    return s;
}

void code_1002()
{
    // Code 1002 is emitted when the compiler tries to
    // parallelize a loop that has an inner loop that
    // has already been parallelized.

#pragma loop(hint_parallel(0))
    for (int i=0; i<1000; ++i) // emit code 1002 for this loop
    {
#pragma loop(hint_parallel(0))
        for (int j=0; j<1000; ++j) // this loop gets parallelized
        {
            A[j] = A[j] + 1;
        }
    }
}

extern "C" void __stosb(unsigned char*, unsigned char, size_t);
void code_1003(unsigned char *dst)
{
    // Code 1003 is emitted when the loop body contains an intrinsic
    // call that may read or write to memory.

    // This can be resolved by using the ivdep pragma.
    // CAUTION -- the compiler will trust your
    // assertion that there are no data dependencies
    // in the loop body. If there are, you are generating
    // code that may have race conditions.

#pragma loop(hint_parallel(0))
    //#pragma loop(ivdep) // ivdep will force this through.
    for (int i=0; i<1000; ++i)
    {
        __stosb(dst, 'c', 10);
        A[i] = A[i] + 1;
    }
}

int code_1004()
{
    // Code 1004 is emitted when there is a scalar reduction
    // in the loop body, which can occur if the loop has been
    // vectorized.

    // You can resolve this by rewriting your code so that it
    // does not have a scalar reduction.

    int s = 0;
#pragma loop(hint_parallel(0))
    for (int i=0; i<1000; ++i)
    {
        s += A[i];
    }
    return s;
}

void code_1005()
{
    // Code 1005 is emitted when the 
    // no_parallel pragma is specified.

#pragma loop(no_parallel)
    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

#include <omp.h>

// Compile with /openmp
void code_1006()
{
    // Code 1006 is emitted when this function contains
    // openmp. Resolve this by removing any openmp in this
    // function.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }

#pragma omp parallel num_threads(4)
    {
        int i = omp_get_thread_num();
        A[i] = A[i] + 1;
    }
}

void code_1007()
{
    // Code 1007 is emitted when the loop induction variable
    // or the loop bounds are not signed 32-bit numbers (int 
    // or long). Resolve this by changing the type of the 
    // induction variable.

#pragma loop(hint_parallel(0))
    for (unsigned int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

void code_1008()
{
    // Code 1008 is emitted when the compiler detects that
    // this loop does not perform enough work to warrant 
    // auto-parallelization.

    // You can resolve this by specifying the hint_parallel
    // pragma. CAUTION -- if the loop does not perform
    // enough work, parallelizing might cause a potentially 
    // large performance penalty.

    // #pragma loop(hint_parallel(0)) //  hint_parallel will force this through
    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

void code_1009()
{
    // Code 1009 is emitted when the compiler tries to parallelize a 
    // "do-while" loop. The auto-parallelizer only targets "for" loops.

    int i = 0;
#pragma loop(hint_parallel(0))
    do
    {
        A[i] = A[i] + 1;
    } 
    while (++i < 1000);
}

110x

110x 原因代码应用于自动向量化。

原因代码

说明

1100

循环包含控制流（例如，“if”或“?”）。

1101

循环包含无法向量化的数据类型转换（可能隐式）。

1102

循环包含非算术或其他非向量化操作。

1103

循环体包括大小在循环内可能会有所不同的移位操作。

1104

循环体包含标量变量。

1105

循环包含无法识别的缩减运算。

1106

未向量化的外部循环。

 
void code_1100(int *A, int x) 
{
    // Code 1100 is emitted when the compiler detects control flow
    // in the loop - for example, "if", the ternary operator "?", and
    // the like. Resolve this by flattening or removing control
    // flow in the loop body.

    // Not all control flow causes 1100; some is indeed  
    // vectorized.

    for (int i=0; i<1000; ++i)
    {
        // straightline code is more amenable to vectorization
        if (x)
        {
            A[i] = A[i] + 1;
        }
    }
}

extern "C" int __readcr0();
void code_1102(int *A)
{
    // Code 1102 is emitted when the compiler is unable to vectorize
    // an operation in the loop body. For example, intrinsics and other
    // non-arithmetic, non-logical, and non-memory operations are not
    // vectorizable.

    // Resolve this by removing as many non-vectorizable operations
    // as possible from the loop body.

    for (int i=0; i<1000; ++i)
    {
        A[i] = __readcr0();
    }
}

void code_1103(int *A, int *B)
{
    // Code 1103 is emitted when the compiler is unable to vectorize
    // a "shift" operation. In this example, there are two shifts
    // that cannot be vectorized.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] >> B[i]; // not vectorizable

        int x = B[i];
        A[i] = A[i] >> x; // not vectorizable
    }

    // To resolve this, ensure that your shift amounts are loop 
    // invariant. If the shift amounts cannot be loop invariant,
    // it may not be possible to vectorize this loop.

    int x = B[0];
    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] >> x; // vectorizable
    }
}

int code_1104(int *A, int *B)
{
    // When it vectorizes a loop, the compiler must 'expand' scalar
    // variables to a vector size such that they can fit in
    // vector registers. Code 1104 is emitted when the compiler
    // cannot 'expand' such scalars.

    // In this example, we try to 'expand' x to be used in the 
    // vectorized loop. However, there is a use of 'x' 
    // beyond the loop body, which prohibits this expansion.

    // To resolve this, try to limit scalars to be used only in
    // the loop body and not beyond, and try to keep their types
    // consistent with the loop types.

    int x;
    for (int i=0; i<1000; ++i)
    {
        x = B[i];
        A[i] = A[i] + x;
    }

    return x;
}

int code_1105(int *A)
{
    // The compiler performs an optimization that's known as "reduction"
    // when it operates on each element of an array and computes
    // a resulting scalar value - for example, in this piece of code, which
    // computes the sum of each element in the array:

    int s = 0;
    for (int i=0; i<1000; ++i)
    {
        s += A[i]; // vectorizable
    }

    // The reduction pattern must resemble the loop in the example. The
    // compiler emits code 1105 if it cannot deduce the reduction
    // pattern, as shown in this example:

    for (int i=0; i<1000; ++i)
    {
        s += A[i] + s;  // code 1105
    }

    // Similarly, reductions of "float" or "double" types require
    // that the /fp:fast switch is thrown. Strictly speaking,
    // the reduction optimization that the compiler performs uses
    // "floating point reassociation". Reassociation is only
    // allowed when /fp:fast is thrown.

    return s;    
}

void code_1106(int *A)
{
    // Code 1106 is emitted when the compiler tries to vectorize
    // an outer loop.

    for (int i=0; i<1000; ++i) // this loop is not vectorized
    {
        for (int j=0; j<1000; ++j) // this loop is vectorized
        {
            A[j] = A[j] + 1;
        }
    }
}

120x

120x 原因代码应用于自动向量化。

原因代码

说明

1200

循环包含阻止向量化的循环携带的数据依赖项。 不同的循环迭代会相互影响，这样向量化循环将产生错误的接听，并且自动向量化不能证明自身没有此类数据依赖项。

1201

数组基础会在循环时更改。

1202

结构中的字段没有 32 或 64 位宽。

1203

循环体包含对数组的非连续访问。

 
void fn();
void code_1200(int *A)
{
    // Code 1200 is emitted when data dependence is prohibiting
    // vectorization. This can only be resolved by rewriting the
    // loop, and considering the marking of loop function calls as 
    // __forceinline.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i-1] + 1; // vectorization-prohibiting
        fn();               // vectorization-prohibiting
    }
}

void code_1201(int *A)
{
    // Code 1201 is emitted when an array base changes
    // in the loop body. Resolve this by rewriting your
    // code so that varying the array base is not necessary.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
        A++;
    }
}

struct S_1202
{
    short a;
    short b;
} s[1000];

short sA[1000], sB[1000], sC[1000];

void code_1202(S_1202 *s)
{
    // Code 1202 is emitted when non-vectorizable struct accesses
    // are present in the loop body. Only struct accesses 
    // that are 32 or 64 bits are vectorized.

    for (int i=0; i<1000; ++i)
    {        
        s[i].a = s[i].b + 1; // this 16 bit struct access is not vectorizable
        sA[i] += sB[i] * sC[i]; // this ensures we don't emit reason code '1300'
    }
}

void code_1203(int *A)
{
    // Code 1203 is emitted when non-vectorizable memory references
    // are present in the loop body. Vectorization of some non-contiguous 
    // memory access is supported - for example, the gather/scatter pattern.

    for (int i=0; i<1000; ++i)
    {
        A[i] += A[0] + 1;       // constant memory access not vectorized
        A[i] += A[i*2+2] + 2;  // non-contiguous memory access not vectorized
    }
}

130x

130x 原因代码应用于自动向量化。

原因代码

说明

1300

循环体不包含计算或包含非常小的计算。

1301

循环步幅不是 +1。

1302

循环是“do-while”。

1303

向量化的循环迭代太少，无法提供值。

1304

循环包含不同大小的分配。

1305

没有足够的类型信息。

 
void code_1300(int *A, int *B)
{
    // Code 1300 is emitted when the compiler detects that there is
    // no computation in the loop body.

    for (int i=0; i<1000; ++i)
    {
        A[i] = B[i]; // Do not vectorize, instead emit memcpy
    }
}

void code_1301(int *A)
{
    // Code 1301 is emitted when the stride of a loop is not positive 1.
    // Only loops that have a stride of positive 1 are vectorized;
    // rewriting your loop may be required.

    for (int i=0; i<1000; i += 2)
    {
        A[i] = A[i] + 1;
    }
}

void code_1302(int *A)
{
    // Code 1302 is emitted for "do-while" loops. Only "while"  
    // and "for" loops are vectorized.

    int i = 0;
    do
    {
        A[i] = A[i] + 1;
    } while (++i < 1000);
}

int code_1303(int *A, int *B)
{
    // Code 1303 is emitted when the compiler detects that
    // the number of iterations of the loop is too small to
    // make vectorization profitable.

    // If the loop computation fits perfectly in 
    // vector registers - for example, the upperbound is 4, or 8 in 
    // this case - then the loop _may_ be vectorized.

    // This loop is not vectorized because there are 5 iterations

    for (int i=0; i<5; ++i)
    {
        A[i] = A[i] + 1;
    }

    // This loop is vectorized

    for (int i=0; i<4; ++i)
    {
        A[i] = A[i] + 1;
    }

    // This loop is not vectorized because runtime pointer checks
    // are required to check that A and B don't overlap. It is not
    // worth it to vectorize this loop.

    for (int i=0; i<4; ++i)
    {
        A[i] = B[i] + 1;
    }

    // This loop is not vectorized because of the scalar reduction.

    int s = 0;
    for (int i=0; i<4; ++i)
    {
        s += A[i];
    }
    return s;
}

void code_1304(int *A, short *B)
{
    // Code 1304 is emitted when the compiler detects
    // different sized statements in the loop body.
    // In this case, there is an 32-bit statement and a
    // 16-bit statement.

    // In cases like this consider splitting the loop into loops to 
    // maximize vector register utilization.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
        B[i] = B[i] + 1;
    }
}

typedef struct S_1305
{
    int a;
    int b;
} S_1305;

void code_1305( S_1305 *s, S_1305 x)
{
    // Code 1305 is emitted when the compiler can't discern
    // proper vectorizable type information for this loop.
    // This includes non-scalar loop types such as struct 
    // assignments, as in this example.

    // Resolve this by ensuring that your loops have statements
    // that operate on integers or floating point types.

    for (int i=0; i<1000; ++i)
    {
        s[i] = x;
    }
}

140x

在指定与自动向量化不兼容的选项时，会出现 140x 原因代码。

原因代码

说明

1400

指定 #pragma loop(no_vector)。

1401

在面向 x86 或 ARM 时，指定 /kernel 开关。

1402

在面向 x86 时，不指定 /arch:SSE2 或更高开关。

1403

指定 /arch:ATOM 开关，且循环包含两倍运算。

1404

指定 /O1 或 /Os 开关。

1405

禁用向量化可帮助动态初始值设定项到静态初始值设定项优化。

 
void code_1400(int *A)
{
    // Code 1400 is emitted when the no_vector pragma 
    // is specified. 

#pragma loop(no_vector)
    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

// Compile with /kernel
void code_1401(int *A)
{
    // Code 1401 is emitted when /kernel is specified.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

// Compile with /arch:IA32
void code_1402(int *A)
{
    // Code 1401 is emitted when /arch:IA32 is specified.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

// Compile with /favor:ATOM
void code_1403(double *A)
{
    // Code 1401 is emitted when /favor:ATOM is specified, and
    // the loop contains operations on "double" arrays.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

// Compile with /O1 or /Os
void code_1404(int *A)
{
    // Code 1401 is emitted when compiling for size.

    for (int i=0; i<1000; ++i)
    {
        A[i] = A[i] + 1;
    }
}

150x

150x 原因代码应用于别名。 当内存中的位置可由两个不同名称访问时，将出现别名。

原因代码

说明

1500

多维数组中的可能别名。

1501

数组结构中的可能别名。

1502

可能的别名和数组索引不包括 n + K。

1503

可能的别名和数组索引有多个偏移量。

1504

可能的别名；需要过多的运行时检查。

1505

可能的别名，但运行时检查太复杂。

 
void code_1500(int A[100][100], int B[100][100])
{
    // Code 1500 is emitted when runtime pointer
    // disambiguation checks are required, and 
    // there are multidimensional array references.

    for (int i=0; i<100; ++i)
    {
        for (int j=0; j<100; ++j)
        {
            A[i][j] = B[i][j] + 1;
        }
    }
}

typedef struct S_1501
{
    int a;
    int b;
} S_1501;

int iA[1000], iB[1000], iC[1000];

void code_1501(S_1501 *s1, S_1501 *s2)
{
    // Code 1501 is emitted when runtime pointer
    // disambiguation checks are required, and 
    // there are array-of-struct accesses in the 
    // loop body.

    for (int i=0; i<100; ++i)
    {
        s1[i].a = s2[i].b + 1;
        iA[i] += iB[i] * iC[i]; // this is to ensure we don't emit reason code '1300'
    }
}

void code_1502(int *A, int *B)
{
    // Code 1502 is emitted when runtime pointer
    // disambiguation checks are required, and 
    // an array reference has an offset that varies 
    // in the loop.

    int x = 0;
    for (int i=0; i<100; ++i)
    {
        A[i] = B[i + x] + 1;
        ++x;                   // 'x' varies in the loop
    }
}

void code_1503(int *A, int *B, int x, int y)
{
    // Code 1503 is emitted when runtime pointer
    // disambiguation checks are required, and 
    // an array reference has multiple offsets.

    for (int i=0; i<100; ++i)
    {
        A[i] = B[i+x] + B[i+y] + 1;   // multiple offsets when addressing 'B': {x, y}
        A[i] = B[i+x] + B[i] + 1;     // multiple offsets when addressing 'B': {x, 0}
        A[i] = B[i+x] + B[i+x] + 1;   // this is vectorized
    }
}

void code_1504(int *A1, int *A2, int *A3, int *A4, 
               int *A5, int *A6, int *A7, int *A8,
               int *A9, int *A10, int *A11, int *A12,
               int *A13, int *A14, int *A15, int *A16)
{
    // Code 1504 is emitted when too many runtime 
    // pointer disambiguation checks are required.

    for (int i=0; i<100; ++i)
    {
        ++A1[i];
        ++A2[i];
        ++A3[i];
        ++A4[i];
        ++A5[i];
        ++A6[i];
        ++A7[i];
        ++A8[i];
        ++A9[i];
        ++A10[i];
        ++A11[i];
        ++A12[i];
        ++A13[i];
        ++A14[i];
        ++A15[i];
        ++A16[i];
    }
}

void code_1505(int *A, int *B)
{
    // Code 1505 is emitted when runtime pointer 
    // disambiguation checks are required, but are
    // too complex for the compiler to discern.

    for (int i=0; i<100; ++i)
    {
        for (int j=0; j<100; ++j)
        {
            for (int k=0; k<100; ++k)
            {
                A[i+j-k] = B[i-j+k] * 2;
            }
        }
    }
}

请参见

参考

自动并行化错误和警告

#pragma loop()

/Q 选项（低级别操作）

/Qpar-report（自动并行化程序报告等级）

/Qvec-report（自动矢量化程序报告等级）

其他资源

本机代码中的并行编程