[llvm] r218838 - PR21101: tablegen's FastISel emitter should filter out unused functions.

[Eric Christopher]

On Wed, Oct 1, 2014 at 5:12 PM, Bob Wilson <bob.wilson at apple.com> wrote:
>
> On Oct 1, 2014, at 4:29 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Wed, Oct 1, 2014 at 3:44 PM, Bob Wilson <bob.wilson at apple.com> wrote:
>>
>> Author: bwilson
>> Date: Wed Oct  1 17:44:01 2014
>> New Revision: 218838
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=218838&view=rev
>> Log:
>> PR21101: tablegen's FastISel emitter should filter out unused functions.
>>
>> FastISel has a fixed set of virtual functions that are overridden by the
>> tablegen-generated code for each target. These functions are distinguished
>> by
>> the kinds of operands, e.g., register + immediate = "ri". The FastISel
>> emitter
>> has been blindly emitting functions with different combinations of operand
>> kinds, even for combinations that are completely unused by FastISel, e.g.,
>> "fastEmit_rrr". Change to filter out functions that will be irrelevant for
>> FastISel and do not bother generating the code for them. Also add explicit
>> "override" keywords for the virtual functions that are overridden.
>
>
> We do seem to have some tests for TableGen under llvm/test/TableGen - is
> this testable?
>
>
> It’s removing dead code, so I do not see any value in testing that.
>
>
> Any data on savings gained by omitting these unused functions?
>
>
> On OS X, the linker will strip dead code so I’m assuming that the end result
> is no change. YMMV on other platforms.

As a note you could check by using -Wl,-no_dead_strip on a mac :)

-eric

>
>
>>
>>
>> Modified:
>>     llvm/trunk/utils/TableGen/FastISelEmitter.cpp
>>
>> Modified: llvm/trunk/utils/TableGen/FastISelEmitter.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/FastISelEmitter.cpp?rev=218838&r1=218837&r2=218838&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/utils/TableGen/FastISelEmitter.cpp (original)
>> +++ llvm/trunk/utils/TableGen/FastISelEmitter.cpp Wed Oct  1 17:44:01 2014
>> @@ -19,6 +19,7 @@
>>
>>  #include "CodeGenDAGPatterns.h"
>>  #include "llvm/ADT/SmallString.h"
>> +#include "llvm/ADT/StringSwitch.h"
>>  #include "llvm/Support/Debug.h"
>>  #include "llvm/Support/ErrorHandling.h"
>>  #include "llvm/TableGen/Error.h"
>> @@ -541,6 +542,17 @@ void FastISelMap::collectPatterns(CodeGe
>>          continue;
>>      }
>>
>> +    // Check if the operands match one of the patterns handled by
>> FastISel.
>> +    std::string ManglingSuffix;
>> +    raw_string_ostream SuffixOS(ManglingSuffix);
>> +    Operands.PrintManglingSuffix(SuffixOS, ImmediatePredicates, true);
>> +    SuffixOS.flush();
>> +    if (!StringSwitch<bool>(ManglingSuffix)
>> +        .Cases("", "r", "rr", "ri", "rf", true)
>> +        .Cases("rri", "i", "f", true)
>> +        .Default(false))
>> +      continue;
>> +
>>      // Get the predicate that guards this pattern.
>>      std::string PredicateCheck = Pattern.getPredicateCheck();
>>
>> @@ -803,7 +815,10 @@ void FastISelMap::printFunctionDefinitio
>>      if (!Operands.empty())
>>        OS << ", ";
>>      Operands.PrintParameters(OS);
>> -    OS << ") {\n";
>> +    OS << ") ";
>> +    if (!Operands.hasAnyImmediateCodes())
>> +      OS << "override ";
>> +    OS << "{\n";
>>
>>      // If there are any forms of this signature available that operate on
>>      // constrained forms of the immediate (e.g., 32-bit sext immediate in
>> a
>>
>>
>> _______________________________________________
>> 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
>