If the compiled program does a shift by a negative amount, combine will
happily work with that, but it shouldn't then do an undefined operation
in GCC itself. This patch fixes the first case mentioned in the bug
report (I haven't been able to reproduce the second case, on trunk at
least).
Bootstrapped and tested on powerpc64-linux, committing to trunk.
Segher
2016-05-13 Segher Boessenkool <seg...@kernel.crashing.org>
PR rtl-optimization/67483
* combine.c (make_compound_operation): Don't call extract_left_shift
with negative shift amounts.
---
gcc/combine.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/gcc/combine.c b/gcc/combine.c
index 02aadc4..b819415 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -8071,6 +8071,7 @@ make_compound_operation (rtx x, enum rtx_code in_code)
&& ! (GET_CODE (lhs) == SUBREG
&& (OBJECT_P (SUBREG_REG (lhs))))
&& CONST_INT_P (rhs)
+ && INTVAL (rhs) >= 0
&& INTVAL (rhs) < HOST_BITS_PER_WIDE_INT
&& INTVAL (rhs) < mode_width
&& (new_rtx = extract_left_shift (lhs, INTVAL (rhs))) != 0)
--
1.9.3
