diff options
author | Ulrich Weigand <uweigand@de.ibm.com> | 2012-02-22 13:22:43 +0100 |
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committer | Ulrich Weigand <uweigand@de.ibm.com> | 2012-02-22 13:22:43 +0100 |
commit | 0bf724bfe6b66c53c81733f663a3e28f2e34dc5d (patch) | |
tree | 84c18aac59cfea12455d1033829110bf8a3b3b45 /gcc/combine.c | |
parent | 96046ea5634e6c92a3b7ef69bdf8acd4d4059c59 (diff) |
2012-02-22 Ulrich Weigand <ulrich.weigand@linaro.org>
gcc/
* combine.c (apply_distributive_law): Do not distribute SUBREG.
2012-02-22 Richard Sandiford <richard.sandiford@linaro.org>
gcc/
* fwprop.c (propagate_rtx): Also set PR_CAN_APPEAR for subregs.
Diffstat (limited to 'gcc/combine.c')
-rw-r--r-- | gcc/combine.c | 46 |
1 files changed, 16 insertions, 30 deletions
diff --git a/gcc/combine.c b/gcc/combine.c index d06de04041e..874b221946f 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -9286,36 +9286,22 @@ apply_distributive_law (rtx x) /* This is also a multiply, so it distributes over everything. */ break; - case SUBREG: - /* Non-paradoxical SUBREGs distributes over all operations, - provided the inner modes and byte offsets are the same, this - is an extraction of a low-order part, we don't convert an fp - operation to int or vice versa, this is not a vector mode, - and we would not be converting a single-word operation into a - multi-word operation. The latter test is not required, but - it prevents generating unneeded multi-word operations. Some - of the previous tests are redundant given the latter test, - but are retained because they are required for correctness. - - We produce the result slightly differently in this case. */ - - if (GET_MODE (SUBREG_REG (lhs)) != GET_MODE (SUBREG_REG (rhs)) - || SUBREG_BYTE (lhs) != SUBREG_BYTE (rhs) - || ! subreg_lowpart_p (lhs) - || (GET_MODE_CLASS (GET_MODE (lhs)) - != GET_MODE_CLASS (GET_MODE (SUBREG_REG (lhs)))) - || paradoxical_subreg_p (lhs) - || VECTOR_MODE_P (GET_MODE (lhs)) - || GET_MODE_SIZE (GET_MODE (SUBREG_REG (lhs))) > UNITS_PER_WORD - /* Result might need to be truncated. Don't change mode if - explicit truncation is needed. */ - || !TRULY_NOOP_TRUNCATION_MODES_P (GET_MODE (x), - GET_MODE (SUBREG_REG (lhs)))) - return x; - - tem = simplify_gen_binary (code, GET_MODE (SUBREG_REG (lhs)), - SUBREG_REG (lhs), SUBREG_REG (rhs)); - return gen_lowpart (GET_MODE (x), tem); + /* This used to handle SUBREG, but this turned out to be counter- + productive, since (subreg (op ...)) usually is not handled by + insn patterns, and this "optimization" therefore transformed + recognizable patterns into unrecognizable ones. Therefore the + SUBREG case was removed from here. + + It is possible that distributing SUBREG over arithmetic operations + leads to an intermediate result than can then be optimized further, + e.g. by moving the outer SUBREG to the other side of a SET as done + in simplify_set. This seems to have been the original intent of + handling SUBREGs here. + + However, with current GCC this does not appear to actually happen, + at least on major platforms. If some case is found where removing + the SUBREG case here prevents follow-on optimizations, distributing + SUBREGs ought to be re-added at that place, e.g. in simplify_set. */ default: return x; |