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| author | Thomas Preud'homme <thomas.preudhomme@arm.com> | 2016-11-25 10:03:46 +0000 |
|---|---|---|
| committer | Thomas Preud'homme <thopre01@gcc.gnu.org> | 2016-11-25 10:03:46 +0000 |
| commit | d8cc3d06f8e365f8c175fbf2923ed15d78ca8510 (patch) | |
| tree | 835f5f5213a2d99a1b6f137d223f61dba6fb05fb /gcc | |
| parent | 83624b6040aaf0039e65b3160fcbc1111def7260 (diff) | |
| download | gcc-d8cc3d06f8e365f8c175fbf2923ed15d78ca8510.zip gcc-d8cc3d06f8e365f8c175fbf2923ed15d78ca8510.tar.gz gcc-d8cc3d06f8e365f8c175fbf2923ed15d78ca8510.tar.bz2 | |
Improve comment for struct symbolic_number in bswap pass
2016-11-25 Thomas Preud'homme <thomas.preudhomme@arm.com>
gcc/
* tree-ssa-math-opts.c (struct symbolic_number): Improve comment.
From-SVN: r242870
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/ChangeLog | 4 | ||||
| -rw-r--r-- | gcc/tree-ssa-math-opts.c | 39 |
2 files changed, 27 insertions, 16 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 69e1235..d739a66 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,5 +1,9 @@ 2016-11-25 Thomas Preud'homme <thomas.preudhomme@arm.com> + * tree-ssa-math-opts.c (struct symbolic_number): Improve comment. + +2016-11-25 Thomas Preud'homme <thomas.preudhomme@arm.com> + PR tree-optimization/77673 * tree-ssa-math-opts.c (struct symbolic_number): Add new src field. (init_symbolic_number): Initialize src field from src parameter. diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c index b0b0c24..4a47254 100644 --- a/gcc/tree-ssa-math-opts.c +++ b/gcc/tree-ssa-math-opts.c @@ -1931,25 +1931,32 @@ make_pass_cse_sincos (gcc::context *ctxt) return new pass_cse_sincos (ctxt); } -/* A symbolic number is used to detect byte permutation and selection - patterns. Therefore the field N contains an artificial number - consisting of octet sized markers: +/* A symbolic number structure is used to detect byte permutation and selection + patterns of a source. To achieve that, its field N contains an artificial + number consisting of BITS_PER_MARKER sized markers tracking where does each + byte come from in the source: - 0 - target byte has the value 0 - FF - target byte has an unknown value (eg. due to sign extension) - 1..size - marker value is the target byte index minus one. + 0 - target byte has the value 0 + FF - target byte has an unknown value (eg. due to sign extension) + 1..size - marker value is the byte index in the source (0 for lsb). To detect permutations on memory sources (arrays and structures), a symbolic - number is also associated a base address (the array or structure the load is - made from), an offset from the base address and a range which gives the - difference between the highest and lowest accessed memory location to make - such a symbolic number. The range is thus different from size which reflects - the size of the type of current expression. Note that for non memory source, - range holds the same value as size. - - For instance, for an array char a[], (short) a[0] | (short) a[3] would have - a size of 2 but a range of 4 while (short) a[0] | ((short) a[0] << 1) would - still have a size of 2 but this time a range of 1. */ + number is also associated: + - a base address BASE_ADDR and an OFFSET giving the address of the source; + - a range which gives the difference between the highest and lowest accessed + memory location to make such a symbolic number; + - the address SRC of the source element of lowest address as a convenience + to easily get BASE_ADDR + offset + lowest bytepos. + + Note 1: the range is different from size as size reflects the size of the + type of the current expression. For instance, for an array char a[], + (short) a[0] | (short) a[3] would have a size of 2 but a range of 4 while + (short) a[0] | ((short) a[0] << 1) would still have a size of 2 but this + time a range of 1. + + Note 2: for non-memory sources, range holds the same value as size. + + Note 3: SRC points to the SSA_NAME in case of non-memory source. */ struct symbolic_number { uint64_t n; |