http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50193
Bug #: 50193
Summary: ARM: ICE on a | (b << negative-constant)
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: michael.h...@linaro.org
trunk r178025, 4.6.1, and 4.5.3 all ICE with unsatisfied constraints on the
following code:
int foo(int a, int b)
{
return a | (b << -3);
}
shift.c: In function 'foo':
shift.c:3:5: warning: left shift count is negative [enabled by default]
shift.c:4:1: error: insn does not satisfy its constraints:
(insn 14 9 17 2 (set (reg/i:SI 0 r0)
(ior:SI (ashift:SI (reg:SI 1 r1 [ b ])
(const_int -3 [0xfffffffffffffffd]))
(reg:SI 0 r0 [ a ]))) shift.c:4 259 {*arith_shiftsi}
(expr_list:REG_DEAD (reg:SI 1 r1 [ b ])
(nil)))
shift.c:4:1: internal compiler error: in extract_constrain_insn_cached, at
recog.c:2030
This happens with -mcpu=cortex-a9 -mthumb. With -marm, GCC recognises that the
shift is unusual, loads it into a register, then uses this in the
register-shifted-register form of ORR. This form isn't available in Thumb-2.
The problem was originally seen in libtheora:lib/mathops.c when built with -O3
-funroll-loops when a shift by negative 8 is generated.
