Bug on both trunk and 4.3.2 [for the latter, change psradi to psrad as the builtin function name changed].
Compiling the following code with -O2 -flax-vector-conversions -mmmx -msse -msse2 generates incorrect code: typedef int v2si __attribute__ ((vector_size (8))); v2si foo (v2si x) { x &= (v2si) 0xffffffffll; x = __builtin_ia32_psradi (x, 1); x &= (v2si) 0x80000000ll; return x; } The compile incorrectly assumes that bit 31 of the shift result always ends up as zero: foo: pxor %xmm0, %xmm0 ret Presumeably, some optimiseration is incorrectly treating the v2si right shift as a 64-bit right shift. [It appears to me that both nonzero_bits1 and num_sign_bit_copies1 can incorrectly optimise vector operation as if they were scalar ops, which is what inspired this example, however, attempting to fix those did not fix this bug, which makes me think the problem is elsewhere.] -- Summary: Incorrect code with MMX right shift __builtin_ia32_psradi Product: gcc Version: 4.3.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: suckfish at ihug dot co dot nz GCC build triplet: x86_64-unknown-linux-gnu GCC host triplet: x86_64-unknown-linux-gnu GCC target triplet: x86_64-unknown-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37809