[LLVMdev] strange dbgs() behavior: unable to print floats in machine backend

[Bjorn De Sutter]

Hi,

that solved my problem on trunk as well, thanks. Strange that you have to include this though.

Bjorn

On 27 Nov 2012, at 00:00, Daniel Prokesch <daniel.prokesch at gmail.com> wrote:

> Hi,
> 
> I accidentally stumbled upon your post.
> I observed similar behaviour whenever I did not include
> 
> #include "llvm/Support/Debug.h"
> #include "llvm/Support/raw_ostream.h"
> 
> I'm working on release 3.1 though.
> 
> hth, Daniel
> 
> On 11/26/2012 03:00 PM, Bjorn De Sutter wrote:
>> Hi,
>> 
>> I am trying to debug my backend, and observe very strange behavior with dbgs():
>> 
>> In the IfConverter, I have added two debugging lines that print floating-point numbers for the sake of demonstration that such printing works fine.
>> 
>> bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
>>                             unsigned Cycle, unsigned Extra,
>>                             const BranchProbability &Prediction) const {
>> 
>>                 dbgs() << "OOPS " << 1.14 << "\n";
>>                 bool flag =  Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
>>                                                    Prediction);
>>                 dbgs() << "OOPS " << 1.15 << "\n";
>>       return flag;
>>     }
>> 
>> This method invokes the backend method
>> 
>> bool ADRESInstrInfo::isProfitableToIfCvt(MachineBasicBlock &MBB, unsigned NumCycles, unsigned ExtraPredCycles,
>>                                          const BranchProbability &Probability) const {
>>      dbgs() << "OOPS " << 1.16 << "\n";
>> }
>> 
>> This invocation works as it should (verified with gdb). But when I execute this code fragment, I get
>> 
>> OOPS 1.140000e+00
>> OOPS %physreg1
>> OOPS 1.150000e+00
>> 
>> So suddenly in the machine backend, the dbgs() ostream (which is still the very same ostream as in the IfConverter, I checked the address with gdb) prints floating point numbers as if they are physical registers. Any idea what is going on or how I can force floating-point numbers to be printed in the backend code? I want to do that to tune my if-predication heuristics ...
>> 
>> By the way, when I step through the isProfitableToIfCvt method, rather than invoking a <<-operator in an ostream class, the constructor of the Twine class is invoked ...
>> 
>> Thanks,
>> 
>> Bjorn De Sutter
>> Computer Systems Lab
>> Ghent University
>> 
>> 
>> 
>> 
>> 
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>