Currently, arithmetic right shifts with a shift count bigger
than the operand size are simplified to zero.
While this makes a lot of sense for LSR and SHL, for ASR it's
much less so.
Remove the simplification and let the back-end generate the code
for a non-immediate count (which is what GCC do).
Note: Some other options would be:
- reduce the shift count module the operand size, like it was
done previously at expansion time and which correspond to the
run-time behaviour of several CPUs families (x86[-64], arm64,
mips, ...) but not all of them (arm, ppc, ...).
- truncate the count to N-1
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 1 -
validation/shift-undef.c | 2 ++
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/simplify.c b/simplify.c
index 0c0f11349..d316367d8 100644
--- a/simplify.c
+++ b/simplify.c
@@ -547,7 +547,6 @@ static int simplify_asr(struct instruction *insn, pseudo_t pseudo, long long val
if (value >= size && !insn->tainted) {
warning(insn->pos, "right shift by bigger than source value");
insn->tainted = 1;
- return replace_with_pseudo(insn, value_pseudo(0));
}
if (!value)
return replace_with_pseudo(insn, pseudo);
diff --git a/validation/shift-undef.c b/validation/shift-undef.c
index e15847a8e..df1ac89e6 100644
--- a/validation/shift-undef.c
+++ b/validation/shift-undef.c
@@ -98,6 +98,7 @@ shift-undef.c:18:30: warning: shift too big (4294967289) for type int
shift-undef.c:19:30: warning: shift too big (4294967288) for type unsigned int
shift-undef.c:20:30: warning: shift too big (4294967287) for type unsigned int
shift-undef.c:21:29: warning: right shift by bigger than source value
+shift-undef.c:24:29: warning: right shift by bigger than source value
shift-undef.c:32:11: warning: shift too big (100) for type int
shift-undef.c:33:11: warning: shift too big (101) for type unsigned int
shift-undef.c:34:11: warning: shift too big (102) for type unsigned int
@@ -117,5 +118,6 @@ shift-undef.c:47:30: warning: shift too big (4294967289) for type int
shift-undef.c:48:30: warning: shift too big (4294967288) for type unsigned int
shift-undef.c:49:30: warning: shift too big (4294967287) for type unsigned int
shift-undef.c:50:26: warning: right shift by bigger than source value
+shift-undef.c:53:26: warning: right shift by bigger than source value
* check-error-end
*/
--
2.18.0
--
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