When the vectorizer detects a widening shift pattern it has to make sure the widening operation is used only once as it will make it part of the recognized pattern.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk. Richard. 2012-06-18 Richard Guenther <rguent...@suse.de> PR tree-optimization/53693 * tree-vect-patterns.c (vect_operation_fits_smaller_type): Reject operands with more than one use. * g++.dg/torture/pr53693.C: New testcase. Index: gcc/tree-vect-patterns.c =================================================================== *** gcc/tree-vect-patterns.c (revision 188725) --- gcc/tree-vect-patterns.c (working copy) *************** vect_operation_fits_smaller_type (gimple *** 991,996 **** --- 991,1001 ---- || TREE_CODE (const_oprnd) != INTEGER_CST) return false; + /* If oprnd has other uses besides that in stmt we cannot mark it + as being part of a pattern only. */ + if (!has_single_use (oprnd)) + return false; + /* If we are in the middle of a sequence, we use DEF from a previous statement. Otherwise, OPRND has to be a result of type promotion. */ if (*new_type) Index: gcc/testsuite/g++.dg/torture/pr53693.C =================================================================== *** gcc/testsuite/g++.dg/torture/pr53693.C (revision 0) --- gcc/testsuite/g++.dg/torture/pr53693.C (revision 0) *************** *** 0 **** --- 1,21 ---- + // { dg-do compile } + + void + filter_scanlines (void *src_buffer, void *dst_buffer, int dst_pitch, int width) + { + int x; + unsigned short *src, *dst_a, *dst_b; + + src = (unsigned short *) src_buffer; + dst_a = (unsigned short *) dst_buffer; + dst_b = ((unsigned short *) dst_buffer) + (dst_pitch >> 1); + + for (x = 0; x < width; x++) + { + unsigned char gs, gh; + gs = src[x]; + gh = gs + (gs >> 1); + dst_a[x] = (gh << 5) | (gh); + dst_b[x] = ((gs - gh) << 5) | (gs - gh); + } + }