void Sub(short * __restrict src1row, short * __restrict src2row, int
num_in_row) {
for(int i=num_in_row; i--;) {
*src1row -= *src2row;
++src1row;
++src2row;
}
}
In the test case above, GCC inserts several explicit conversions soon after the
gimple transformation stage and gets,
D.2097 = *src1row;
D.2098 = (short unsigned int) D.2097;
D.2099 = *src2row;
D.2100 = (short unsigned int) D.2099;
D.2101 = D.2098 - D.2100;
D.2102 = (short int) D.2101;
These conversions breaks the vectorization and GCC reports,
/* i686-unknown-linux-gnu-gcc -O3 -ftree-vectorize -ftree-vectorizer-verbose=5
-march=nocona -fno-strict-aliasing -c test.cc */
......
test.cc:2: note: not vectorized: relevant stmt not supported: D.2430_11 =
(short unsigned int) D.2429_10
test.cc:1: note: vectorized 0 loops in function.
--
Summary: Unnecessary conversion from short to unsigend short
breaks vectorization
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gangren at google dot com
GCC build triplet: i686-unknown-linux-gnu-gcc
GCC host triplet: i686-unknown-linux-gnu-gcc
GCC target triplet: i686-unknown-linux-gnu-gcc
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32309
