sparse contains some code to simplify an AND masking
followed by a truncating cast.
However, this simplification is problematic because it
doesn't keep the sizes consistent. For example, code like:
and.32 %r3 <- %r2, $0x7fff
trunc.16 %r4 <- (32) %r3
will be discarded with %r3 used in place of %r4.
This is correct in the mathematical sense but %r4 had a size
of 16 while %r3 has a size of 32, so using %r3 in place of %r4
will make the sizes inconsistent with unexpected consequences.
We can more or less fix this by using another transformation
that preserve the sizes:
trunc.16 %r3 <- (32) %r2
and.16 %r4 <- %r3, $0x7fff
which in itself doesn't optimize anything but:
1) the mask may be smaller
2) may trigger other simplification with the TRUNC or the AND.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 17 +++++++++++------
validation/optim/and-trunc.c | 1 -
2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/simplify.c b/simplify.c
index 0982d9d4b..336339fac 100644
--- a/simplify.c
+++ b/simplify.c
@@ -999,10 +999,18 @@ static int simplify_cast(struct instruction *insn)
/* A cast of a AND might be a no-op.. */
switch (insn->opcode) {
case OP_TRUNC:
+ if (nbr_users(src) > 1)
+ break;
+ def->opcode = OP_TRUNC;
+ def->orig_type = def->type;
+ def->type = insn->type;
+ def->size = size;
+
+ insn->opcode = OP_AND;
mask = val->value;
- if (!(mask >> (size-1)))
- goto simplify;
- break;
+ mask &= (1ULL << size) - 1;
+ insn->src2 = value_pseudo(mask);
+ return REPEAT_CSE;
}
break;
case OP_TRUNC:
@@ -1029,9 +1037,6 @@ static int simplify_cast(struct instruction *insn)
}
return 0;
-
-simplify:
- return replace_with_pseudo(insn, src);
}
static int simplify_select(struct instruction *insn)
diff --git a/validation/optim/and-trunc.c b/validation/optim/and-trunc.c
index bcb80bbe0..df1e4d03e 100644
--- a/validation/optim/and-trunc.c
+++ b/validation/optim/and-trunc.c
@@ -11,7 +11,6 @@ short umask(unsigned short x)
/*
* check-name: and-trunc
* check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
*
* check-output-ignore
* check-output-excludes: sext\\.
--
2.18.0
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