I am trying to vectorize the function
void bar(float *c, float *a, float *b)
{
const int width = 256;
for (int i = 0 ; i < 256 ; ++i ) {
c[ i ] = a[ i ] + b[ i ];
c[ width + i ] = a[ width + i ] + b[ width + i ];
}
}
using the following commands
clang -emit-llvm -S loop.c
opt loop.ll -O3 -debug-only=loop-vectorize -S -o -
LV: Checking a loop in "bar"
LV: Found a loop: for.body
LV: Found an induction variable.
LV: Found an unidentified write ptr: float* %c
LV: Found an unidentified write ptr: float* %c
LV: Found an unidentified read ptr: float* %a
LV: Found an unidentified read ptr: float* %b
LV: Found an unidentified read ptr: float* %a
LV: Found an unidentified read ptr: float* %b
LV: Found a runtime check ptr: %arrayidx4 = getelementptr inbounds
float* %c, i64 %indvars.iv
LV: Found a runtime check ptr: %arrayidx14 = getelementptr inbounds
float* %c, i64 %2
LV: Found a runtime check ptr: %arrayidx = getelementptr inbounds
float* %a, i64 %indvars.iv
LV: Found a runtime check ptr: %arrayidx2 = getelementptr inbounds
float* %b, i64 %indvars.iv
LV: Found a runtime check ptr: %arrayidx7 = getelementptr inbounds
float* %a, i64 %2
LV: Found a runtime check ptr: %arrayidx10 = getelementptr inbounds
float* %b, i64 %2
LV: We need to do 10 pointer comparisons.
LV: We can't vectorize because we can't find the array bounds.
LV: Can't vectorize due to memory conflicts
LV: Not vectorizing.
Is there any chance to make this work?
Frank
----- Original Message -----> I am trying to vectorize the function > > void bar(float *c, float *a, float *b) > { > const int width = 256; > for (int i = 0 ; i < 256 ; ++i ) { > c[ i ] = a[ i ] + b[ i ]; > c[ width + i ] = a[ width + i ] + b[ width + i ]; > } > } > > using the following commands > > clang -emit-llvm -S loop.c > opt loop.ll -O3 -debug-only=loop-vectorize -S -o - > > LV: Checking a loop in "bar" > LV: Found a loop: for.body > LV: Found an induction variable. > LV: Found an unidentified write ptr: float* %c > LV: Found an unidentified write ptr: float* %c > LV: Found an unidentified read ptr: float* %a > LV: Found an unidentified read ptr: float* %b > LV: Found an unidentified read ptr: float* %a > LV: Found an unidentified read ptr: float* %b > LV: Found a runtime check ptr: %arrayidx4 = getelementptr inbounds > float* %c, i64 %indvars.iv > LV: Found a runtime check ptr: %arrayidx14 = getelementptr inbounds > float* %c, i64 %2 > LV: Found a runtime check ptr: %arrayidx = getelementptr inbounds > float* %a, i64 %indvars.iv > LV: Found a runtime check ptr: %arrayidx2 = getelementptr inbounds > float* %b, i64 %indvars.iv > LV: Found a runtime check ptr: %arrayidx7 = getelementptr inbounds > float* %a, i64 %2 > LV: Found a runtime check ptr: %arrayidx10 = getelementptr inbounds > float* %b, i64 %2 > LV: We need to do 10 pointer comparisons. > LV: We can't vectorize because we can't find the array bounds. > LV: Can't vectorize due to memory conflicts > LV: Not vectorizing. > > Is there any chance to make this work?Try adding the restrict keyword to the function parameters: void bar(float * restrict c, float * restrict a, float * restrict b) -Hal> > Frank > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-- Hal Finkel Assistant Computational Scientist Leadership Computing Facility Argonne National Laboratory
Bingo! That works (when coming from C source)
Now, I have a serious problem. I am not coming from C but I build the
function with the builder. I am also forced to change the signature and
load the pointers a,b,c afterwards:
define void @bar([8 x i8]* nocapture readonly %arg_ptr) #0 {
entrypoint:
%0 = bitcast [8 x i8]* %arg_ptr to i32*
%1 = load i32* %0, align 4
%2 = getelementptr [8 x i8]* %arg_ptr, i64 1
%3 = bitcast [8 x i8]* %2 to i32*
%4 = load i32* %3, align 4
%5 = getelementptr [8 x i8]* %arg_ptr, i64 2
%6 = bitcast [8 x i8]* %5 to float**
%7 = load float** %6, align 8
%8 = getelementptr [8 x i8]* %arg_ptr, i64 3
%9 = bitcast [8 x i8]* %8 to float**
%10 = load float** %9, align 8
%11 = getelementptr [8 x i8]* %arg_ptr, i64 4
%12 = bitcast [8 x i8]* %11 to float**
%13 = load float** %12, align 8
%14 = sext i32 %1 to i64
br label %L0
Now, these pointer (%7,%10,%13) are not qualified with 'restrict' and
the loop vectorizer gives me the same message:
LV: We can't vectorize because we can't find the array bounds.
LV: Can't vectorize due to memory conflicts
LV: Not vectorizing.
I asked this a few days ago; now it comes up again: Is there a way to
qualify a pointer/Value to be 'restrict'?
Another possible solution would be telling the loop vectorizer that it's
safe to treat all arrays as disjunct. Is this possible?
Frank
On 28/10/13 15:11, Hal Finkel wrote:> ----- Original Message -----
>> I am trying to vectorize the function
>>
>> void bar(float *c, float *a, float *b)
>> {
>> const int width = 256;
>> for (int i = 0 ; i < 256 ; ++i ) {
>> c[ i ] = a[ i ] + b[ i ];
>> c[ width + i ] = a[ width + i ] + b[ width + i ];
>> }
>> }
>>
>> using the following commands
>>
>> clang -emit-llvm -S loop.c
>> opt loop.ll -O3 -debug-only=loop-vectorize -S -o -
>>
>> LV: Checking a loop in "bar"
>> LV: Found a loop: for.body
>> LV: Found an induction variable.
>> LV: Found an unidentified write ptr: float* %c
>> LV: Found an unidentified write ptr: float* %c
>> LV: Found an unidentified read ptr: float* %a
>> LV: Found an unidentified read ptr: float* %b
>> LV: Found an unidentified read ptr: float* %a
>> LV: Found an unidentified read ptr: float* %b
>> LV: Found a runtime check ptr: %arrayidx4 = getelementptr inbounds
>> float* %c, i64 %indvars.iv
>> LV: Found a runtime check ptr: %arrayidx14 = getelementptr inbounds
>> float* %c, i64 %2
>> LV: Found a runtime check ptr: %arrayidx = getelementptr inbounds
>> float* %a, i64 %indvars.iv
>> LV: Found a runtime check ptr: %arrayidx2 = getelementptr inbounds
>> float* %b, i64 %indvars.iv
>> LV: Found a runtime check ptr: %arrayidx7 = getelementptr inbounds
>> float* %a, i64 %2
>> LV: Found a runtime check ptr: %arrayidx10 = getelementptr inbounds
>> float* %b, i64 %2
>> LV: We need to do 10 pointer comparisons.
>> LV: We can't vectorize because we can't find the array bounds.
>> LV: Can't vectorize due to memory conflicts
>> LV: Not vectorizing.
>>
>> Is there any chance to make this work?
> Try adding the restrict keyword to the function parameters:
>
> void bar(float * restrict c, float * restrict a, float * restrict b)
>
> -Hal
>
>> Frank
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>