In an expression like OP((x | C), K), if the effective mask (M)
corresponding to OP(_, K) is equal to the combined mask (C & M),
then the OR operation is unneeded and can be replaced by M itself,
giving: OP(M, K).
In mathematical terms:
0) ((x | C) & M) = ((x & M) | (C & M))
1) (C & M) = M
2) ((x & M) | (C & M)) = ((x & M) | M) = M
and so OP((x | C), K) -> OP(M, K).
For example, code like:
unsigned int foo(int x)
{
return (x | 7) & 2;
}
is now simplified into:
foo:
ret.32 $2
which previously was not optimized
foo:
or.32 %r2 <- %arg1, $7
and.32 %r3 <- %r2, $2
ret.32 %r3
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 4 ++++
validation/optim/and-or-constant1.c | 1 -
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/simplify.c b/simplify.c
index 6c4546fcb..a36083789 100644
--- a/simplify.c
+++ b/simplify.c
@@ -622,6 +622,10 @@ static int simplify_mask_or(struct instruction *insn, unsigned long long mask, s
// if (C & M) == 0: OR(x, C) -> x
return replace_pseudo(insn, &insn->src1, src1);
}
+ if (nval == mask) {
+ // if (C & M) == M: OR(x, C) -> M
+ return replace_pseudo(insn, &insn->src1, value_pseudo(mask));
+ }
}
return 0;
}
diff --git a/validation/optim/and-or-constant1.c b/validation/optim/and-or-constant1.c
index 3f1c90528..49823d5ca 100644
--- a/validation/optim/and-or-constant1.c
+++ b/validation/optim/and-or-constant1.c
@@ -6,7 +6,6 @@ int foo(int x)
/*
* check-name: or-and-constant1
* check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
*
* check-output-ignore
* check-output-contains: ret\\..*\\$0xfff
--
2.18.0
