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Diffstat (limited to 'results/classifier/108/none/852')
| -rw-r--r-- | results/classifier/108/none/852 | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/results/classifier/108/none/852 b/results/classifier/108/none/852 new file mode 100644 index 00000000..ed371795 --- /dev/null +++ b/results/classifier/108/none/852 @@ -0,0 +1,46 @@ +device: 0.591 +performance: 0.553 +semantic: 0.431 +permissions: 0.377 +vnc: 0.370 +PID: 0.348 +socket: 0.318 +graphic: 0.307 +files: 0.288 +debug: 0.280 +network: 0.259 +other: 0.088 +boot: 0.083 +KVM: 0.042 + +ppc64le: possible SIMD issue casting double to int +Description of problem: +Working with numpy in a ppc64le VM, I ran into a strange double -to casting issue, specifically when casting an array of 1.0 values to 1 values. The numpy folks guided me to a small reproducible test case. + +The attached [convert.c](/uploads/2dd7936f4defccf816ffee7c7c002e77/convert.c) creates double and int arrays of length `1 <= n <= 16`. The double array is filled with the value 1.0, and both arrays are passed to a function that converts the value. + +With `-O2`, output is as expected (truncated here): + +``` +i = 1: 1 +i = 2: 1 1 +i = 3: 1 1 1 +i = 4: 1 1 1 1 +i = 5: 1 1 1 1 1 +i = 6: 1 1 1 1 1 1 +``` + +With `-O3`, all values that fit into blocks of four become zero: +``` +i = 1: 1 +i = 2: 1 1 +i = 3: 1 1 1 +i = 4: 0 0 0 0 +i = 5: 0 0 0 0 1 +i = 6: 0 0 0 0 1 1 +``` + +I tested this with executables compiled on a physical ppc64le host, where the issue is not reproducible. +Steps to reproduce: +1. `gcc -O2 -o convert convert.c && ./convert` +2. `gcc -O3 -o convert convert.c && ./convert` |