https://llvm.org/bugs/show_bug.cgi?id=25321
Bug ID: 25321
Summary: SciMark performance regression since r246985
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: yaron.ke...@gmail.com
CC: dsch...@google.com, j...@google.com,
llvm-bugs@lists.llvm.org, rjmcc...@apple.com
Classification: Unclassified
SciMark2 MonteCarlo performance had regressed to less than half in r246985.
To reproduce, download http://math.nist.gov/scimark2/scimark2_1c.zip and open
it somewhere. Compile and run the benchmark with
>clang -o scimark2 -O2 *.c
>./scimark2
and look at the MonteCarlo results.
Comparing gcc 5.1, clang r246984, clang r246985 and r251299 (current svn),
gcc 5.1 and clang r246984 MonteCarlo performance are similar, although gcc
takes the lead.
clang r246985 performance was cut to less than half and stayed the same in
current svn. This may be a result of the code generated to access
Random_struct, when 17 is changed into 18
typedef struct
{
int m[17];
int seed;
int i; /* originally = 4 */
with
typedef struct
{
int m[18];
int seed;
int i; /* originally = 4 */
the performance regression is gone.
>uname -a
Linux PC 3.16.0-51-generic #69~14.04.1-Ubuntu SMP Wed Oct 7 15:32:41 UTC 2015
x86_64 x86_64 x86_64 GNU/Linux
>~/bug$ gcc -v 2>&1 | grep version
gcc version 5.1.0 (Ubuntu 5.1.0-0ubuntu11~14.04.1)
>~/bug$ gcc -O2 scimark2/*.c -o scimark -lm
./scimark | grep MonteCarlo
>~/bug$ ./scimark | grep MonteCarlo
MonteCarlo: Mflops: 672.76
>~/bug$ llvm/bin/clang -v 2>&1 | grep version
llvmclang version 3.8.0 (trunk 246984)
>~/bug$ llvm/bin/clang -O2 scimark2/*.c -o scimark -lm
./scimark | grep MonteCarlo
>~/bug$ ./scimark | grep MonteCarlo
MonteCarlo: Mflops: 631.23
>~/bug$ llvm/fast/bin/clang -v 2>&1 | grep version
llvm/fast/bin/clang clang version 3.8.0 (trunk 246985)
>~/bug$ llvm/fast/bin/clang -O2 scimark2/*.c -o scimark -lm
./scimark | grep MonteCarlo
>~/bug$ ./scimark | grep MonteCarlo
MonteCarlo: Mflops: 270.40
>~/bug$ llvm/fast/bin/clang -v 2>&1 | grep version
llvm/fast/bin/clang -O2 scimark2/*.c -o scimark -lm
clang version 3.8.0 (trunk 251299)
.>~/bug$ llvm/fast/bin/clang -O2 scimark2/*.c -o scimark -lm
cimark | grep MonteCarlo
>~/bug$ ./scimark | grep MonteCarlo
MonteCarlo: Mflops: 266.42
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