The instructions LSR(AND(x, M), S) are already simplified into
AND(LSR(x, S), (M >> 12)) but only if AND(x, M) has a single user.
However, if (M >> S) == 0, they can always directly be simplified to 0.
For example code like:
unsigned foo(unsigned x)
{
unsigned t = (x & 0x00000fff);
return (t >> 12) & t;
}
is now simplified into:
foo:
ret.32 $0
while previously it was:
foo:
and.32 %r2 <- %arg1, $0xfff
lsr.32 %r4 <- %r2, $12
and.32 %r6 <- %r4, %r2
ret.32 %r6
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 6 +++++-
validation/optim/lsr-and0.c | 1 -
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/simplify.c b/simplify.c
index c18965bfa..fe264417e 100644
--- a/simplify.c
+++ b/simplify.c
@@ -590,7 +590,7 @@ static int simplify_or_lsr(struct instruction *insn, pseudo_t src, pseudo_t othe
static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long value)
{
struct instruction *def;
- unsigned long long mask, omask;
+ unsigned long long mask, omask, nmask;
unsigned long long nval;
unsigned int size;
pseudo_t src2;
@@ -649,7 +649,11 @@ static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long v
// by (A >> S) & (M >> S)
if (!constant(def->src2))
break;
+ mask = bits_mask(insn->size - value) << value;
omask = def->src2->value;
+ nmask = omask & mask;
+ if (nmask == 0)
+ return replace_with_pseudo(insn, value_pseudo(0));
if (nbr_users(pseudo) > 1)
break;
def->opcode = OP_LSR;
diff --git a/validation/optim/lsr-and0.c b/validation/optim/lsr-and0.c
index 292c0332f..94310ba8a 100644
--- a/validation/optim/lsr-and0.c
+++ b/validation/optim/lsr-and0.c
@@ -7,7 +7,6 @@ unsigned lsr_and0(unsigned x)
/*
* check-name: lsr-and0
* check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
*
* check-output-ignore
* check-output-contains: ret\\..*\\$0$
--
2.18.0
