llvm dev - Apr 2014 - [LLVMdev] llvm cse optimization

I'm working on the across the subprogram call optimization, and let's
say the following llvm IR,
 
 @ng0 = internal global [2 x i32] [i32 2, i32 0], align 4
 
  %t7 = alloca [16 x i8], align 16
  %add.ptr = getelementptr inbounds i8* %t1, i64 40
  %call = call i8* @handle_value(i8* %add.ptr, i32 3) #3
  %arraydecay = getelementptr inbounds [8 x i8]* %t3, i64 0, i64 0
  %arraydecay1 = getelementptr inbounds [16 x i8]* %t4, i64 0, i64 0
 call void @select_value(i8* %arraydecay, i32 1, i32 1, i8* %call, i8*
%arraydecay1, i8* null, i32 1, i32 2, i32 1, i8* bitcast ([2 x i32]* @ng0 to
i8*), i32 32, i32 1) #3
  %call3 = call i8* @handle_value(i8* %add.ptr, i32 3) #3
 
; Function Attrs: nounwind readonly
declare i8* @handle_value(i8* nocapture, i32) #1
; Function Attrs: nounwind
declare void @select_value(i8*, i32, i32, i8* nocapture readonly, i8* nocapture
readonly, i8*, i32, i32, i32, i8*, i32, i32) #2 //select value will only write
to the first parameter, other parameter is readonly
 
For the above case, the second handle_value function call should be replaced
with %call with cse or gvn optimization.
 
Is anything I can do to optimize this case?
 
thanks

 		 	   		  
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On Apr 11, 2014, at 10:13 AM, xiaoyong liu <xiaoyongliu at outlook.com>
wrote:
> I'm working on the across the subprogram call optimization, and
let's say the following llvm IR,
>  
>  @ng0 = internal global [2 x i32] [i32 2, i32 0], align 4
>  
>   %t7 = alloca [16 x i8], align 16
>   %add.ptr = getelementptr inbounds i8* %t1, i64 40
>   %call = call i8* @handle_value(i8* %add.ptr, i32 3) #3
>   %arraydecay = getelementptr inbounds [8 x i8]* %t3, i64 0, i64 0
>   %arraydecay1 = getelementptr inbounds [16 x i8]* %t4, i64 0, i64 0
>  call void @select_value(i8* %arraydecay, i32 1, i32 1, i8* %call, i8*
%arraydecay1, i8* null, i32 1, i32 2, i32 1, i8* bitcast ([2 x i32]* @ng0 to
i8*), i32 32, i32 1) #3
>   %call3 = call i8* @handle_value(i8* %add.ptr, i32 3) #3
>  
> ; Function Attrs: nounwind readonly
> declare i8* @handle_value(i8* nocapture, i32) #1
> ; Function Attrs: nounwind
> declare void @select_value(i8*, i32, i32, i8* nocapture readonly, i8*
nocapture readonly, i8*, i32, i32, i32, i8*, i32, i32) #2 //select value will
only write to the first parameter, other parameter is readonly
The function ’select_value’ is not marked as *not* having side effects. They
compiler has to assume that it could write to memory or print to the screen so
it can’t merge them.
>  
> For the above case, the second handle_value function call should be
replaced with %call with cse or gvn optimization.
>  
> Is anything I can do to optimize this case?
>  
> thanks
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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Here, The function ’select_value’, which is an external function,  only write to
the first parameter and other parameters are readonly and no global value
writing.
As what I know, we didn't have an attribute for this case to indict only
writing to the first actual parameter.
We should mark the first parameter as Mod, others as Ref and let cse work for
readonly arguments.
 
Pls kindly let me know If you know any way to mark the function to ONLY kill the
first parameter for the general optimization.
 
thanks
xiaoyong
 
Subject: Re: [LLVMdev] llvm cse optimization
From: nrotem at apple.com
Date: Fri, 11 Apr 2014 10:25:57 -0700
CC: llvmdev at cs.uiuc.edu
To: xiaoyongliu at outlook.com


On Apr 11, 2014, at 10:13 AM, xiaoyong liu <xiaoyongliu at outlook.com>
wrote:I'm working on the across the subprogram call optimization, and
let's say the following llvm IR,
 
 @ng0 = internal global [2 x i32] [i32 2, i32 0], align 4
 
  %t7 = alloca [16 x i8], align 16
  %add.ptr = getelementptr inbounds i8* %t1, i64 40
  %call = call i8* @handle_value(i8* %add.ptr, i32 3) #3
  %arraydecay = getelementptr inbounds [8 x i8]* %t3, i64 0, i64 0
  %arraydecay1 = getelementptr inbounds [16 x i8]* %t4, i64 0, i64 0
 call void @select_value(i8* %arraydecay, i32 1, i32 1, i8* %call, i8*
%arraydecay1, i8* null, i32 1, i32 2, i32 1, i8* bitcast ([2 x i32]* @ng0 to
i8*), i32 32, i32 1) #3
  %call3 = call i8* @handle_value(i8* %add.ptr, i32 3) #3
 
; Function Attrs: nounwind readonly
declare i8* @handle_value(i8* nocapture, i32) #1
; Function Attrs: nounwind
declare void @select_value(i8*, i32, i32, i8* nocapture readonly, i8* nocapture
readonly, i8*, i32, i32, i32, i8*, i32, i32) #2 //select value will only write
to the first parameter, other parameter is readonly

The function ’select_value’ is not marked as *not* having side effects. They
compiler has to assume that it could write to memory or print to the screen so
it can’t merge them.
 
For the above case, the second handle_value function call should be replaced
with %call with cse or gvn optimization.
 
Is anything I can do to optimize this case?
 
thanks

_______________________________________________
LLVM Developers mailing list
LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
 		 	   		  
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