[llvm-commits] [llvm] r162873 - in /llvm/trunk: include/llvm/Support/Compiler.h lib/Support/raw_ostream.cpp

[Benjamin Kramer]

On 03.09.2012, at 16:43, Jakub Staszak <kubastaszak at gmail.com> wrote:

> BUILTIN_EXPECT also supported SwitchInst, which is impossible for LLVM_LIKELY. Nobody probably ever used that though. Also, you may want to upgrade docs/BranchWeightMetadata.html.

This isn't about the representation of __builtin_expect in llvm IR, it's just a portable macro to allow using __builtin_expect to optimize llvm itself. __builtin_expect is a rather low-level thing and for the specific uses in LLVM the LIKELY/UNLIKELY macros provide an easier interface.

- Ben

> - Kuba
> 
> On Aug 30, 2012, at 1:30 AM, Benjamin Kramer <benny.kra at gmail.com> wrote:
> 
>> 
>> On 30.08.2012, at 01:18, Chandler Carruth <chandlerc at google.com> wrote:
>> 
>>> On Wed, Aug 29, 2012 at 3:57 PM, Benjamin Kramer <benny.kra at googlemail.com> wrote:
>>> Author: d0k
>>> Date: Wed Aug 29 17:57:00 2012
>>> New Revision: 162873
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=162873&view=rev
>>> Log:
>>> Replace the BUILTIN_EXPECT macro with a less horrible LLVM_LIKELY/LLVM_UNLIKELY interface.
>>> 
>>> Modified:
>>>   llvm/trunk/include/llvm/Support/Compiler.h
>>>   llvm/trunk/lib/Support/raw_ostream.cpp
>>> 
>>> Modified: llvm/trunk/include/llvm/Support/Compiler.h
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Compiler.h?rev=162873&r1=162872&r2=162873&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/Support/Compiler.h (original)
>>> +++ llvm/trunk/include/llvm/Support/Compiler.h Wed Aug 29 17:57:00 2012
>>> @@ -106,9 +106,11 @@
>>> #endif
>>> 
>>> #if (__GNUC__ >= 4)
>>> -#define BUILTIN_EXPECT(EXPR, VALUE) __builtin_expect((EXPR), (VALUE))
>>> +#define LLVM_LIKELY(EXPR) __builtin_expect((EXPR), true)
>>> +#define LLVM_UNLIKELY(EXPR) __builtin_expect((EXPR), false)
>>> 
>>> Do you want to cast (EXPR) to bool before handing it to __builtin_expect? The true variant will do the wrong thing for integers in some weird cases without that...
>> 
>> Yup, that's safer and better fits the if(LLVM_LIKELY(…)) idiom. Added bool casts in r162877.
>> 
>> - Ben
>> 
>>> 
>>> #else
>>> -#define BUILTIN_EXPECT(EXPR, VALUE) (EXPR)
>>> +#define LLVM_LIKELY(EXPR) (EXPR)
>>> +#define LLVM_UNLIKELY(EXPR) (EXPR)
>>> #endif
>>> 
>>> 
>>> 
>>> Modified: llvm/trunk/lib/Support/raw_ostream.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/raw_ostream.cpp?rev=162873&r1=162872&r2=162873&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Support/raw_ostream.cpp (original)
>>> +++ llvm/trunk/lib/Support/raw_ostream.cpp Wed Aug 29 17:57:00 2012
>>> @@ -266,8 +266,8 @@
>>> 
>>> raw_ostream &raw_ostream::write(unsigned char C) {
>>>  // Group exceptional cases into a single branch.
>>> -  if (BUILTIN_EXPECT(OutBufCur >= OutBufEnd, false)) {
>>> -    if (BUILTIN_EXPECT(!OutBufStart, false)) {
>>> +  if (LLVM_UNLIKELY(OutBufCur >= OutBufEnd)) {
>>> +    if (LLVM_UNLIKELY(!OutBufStart)) {
>>>      if (BufferMode == Unbuffered) {
>>>        write_impl(reinterpret_cast<char*>(&C), 1);
>>>        return *this;
>>> @@ -286,8 +286,8 @@
>>> 
>>> raw_ostream &raw_ostream::write(const char *Ptr, size_t Size) {
>>>  // Group exceptional cases into a single branch.
>>> -  if (BUILTIN_EXPECT(size_t(OutBufEnd - OutBufCur) < Size, false)) {
>>> -    if (BUILTIN_EXPECT(!OutBufStart, false)) {
>>> +  if (LLVM_UNLIKELY(size_t(OutBufEnd - OutBufCur) < Size)) {
>>> +    if (LLVM_UNLIKELY(!OutBufStart)) {
>>>      if (BufferMode == Unbuffered) {
>>>        write_impl(Ptr, Size);
>>>        return *this;
>>> @@ -302,7 +302,7 @@
>>>    // If the buffer is empty at this point we have a string that is larger
>>>    // than the buffer. Directly write the chunk that is a multiple of the
>>>    // preferred buffer size and put the remainder in the buffer.
>>> -    if (BUILTIN_EXPECT(OutBufCur == OutBufStart, false)) {
>>> +    if (LLVM_UNLIKELY(OutBufCur == OutBufStart)) {
>>>      size_t BytesToWrite = Size - (Size % NumBytes);
>>>      write_impl(Ptr, BytesToWrite);
>>>      copy_to_buffer(Ptr + BytesToWrite, Size - BytesToWrite);
>>> @@ -523,7 +523,7 @@
>>>    ssize_t ret;
>>> 
>>>    // Check whether we should attempt to use atomic writes.
>>> -    if (BUILTIN_EXPECT(!UseAtomicWrites, true)) {
>>> +    if (LLVM_LIKELY(!UseAtomicWrites)) {
>>>      ret = ::write(FD, Ptr, Size);
>>>    } else {
>>>      // Use ::writev() where available.
>>> 
>>> 
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>> 
>> 
>> 
>> _______________________________________________
>> llvm-commits mailing list
>> llvm-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>