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| author | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-07-02 15:34:38 +0200 |
|---|---|---|
| committer | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-07-23 13:11:20 +0200 |
| commit | 780d796a478f686379489fc2e02f932e7dcd67e9 (patch) | |
| tree | b929c5c53cb2cb309166cda96eb4f5f56e1bc0fd /simplify.c | |
| parent | 45e70ebf4685004ad3cf31c8acf5b8c834933379 (diff) | |
| download | sparse-dev-780d796a478f686379489fc2e02f932e7dcd67e9.tar.gz | |
cast: simplify [ZS]EXT(AND(x,M),N)
A OP_AND with a constant value followed by a sign or zero-extension
can often be moved after the extension.
This is good because it can trigger the cancellation of the OP[ZS]EXT
with a preceding OP_TRUNC, a common situation with bitfields.
Note: This 'simplification' is less desirable if there is
no preceding OP_TRUNC, for example, in a sequence like:
and.32 %t <- %a, $mask
*ext.64 %r <- %t
If needed, this can be filtered out at some later stage.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Diffstat (limited to 'simplify.c')
| -rw-r--r-- | simplify.c | 24 |
1 files changed, 24 insertions, 0 deletions
@@ -1011,6 +1011,30 @@ static int simplify_cast(struct instruction *insn) mask &= (1ULL << size) - 1; insn->src2 = value_pseudo(mask); return REPEAT_CSE; + + case OP_SEXT: + if (val->value & (1 << (def->size - 1))) + break; + // OK, sign bit is 0 + case OP_ZEXT: + if (nbr_users(src) > 1) + break; + // transform: + // and.n %b <- %a, M + // *ext.m %c <- (n) %b + // into: + // zext.m %b <- %a + // and.m %c <- %b, M + // For ZEXT, the mask will always be small + // enough. For SEXT, it can only be done if + // the mask force the sign bit to 0. + def->opcode = OP_ZEXT; + def->orig_type = insn->orig_type; + def->type = insn->type; + def->size = insn->size; + insn->opcode = OP_AND; + insn->src2 = val; + return REPEAT_CSE; } break; case OP_TRUNC: |