This PR is a wrong-code bug caused by the over-widening support. The minimum input precisions for a COND_EXPR are supposed to apply only to the "then" and "else" values, but here we were applying them to the operands of a nested COND_EXPR comparison instead.
Tested on aarch64-linux-gnu (with and without SVE), aarch64_be-elf and x86_64-linux-gnu. OK to install? Richard 2018-08-01 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR tree-optimization/86749 * tree-vect-patterns.c (vect_determine_min_output_precision_1): If the lhs is used in a COND_EXPR, check that it is being used as the "then" or "else" value. gcc/testsuite/ PR tree-optimization/86749 * gcc.dg/vect/pr86749.c: New test. Index: gcc/tree-vect-patterns.c =================================================================== --- gcc/tree-vect-patterns.c 2018-07-31 15:26:37.102461003 +0100 +++ gcc/tree-vect-patterns.c 2018-08-01 10:12:45.865913009 +0100 @@ -4399,6 +4399,14 @@ vect_determine_min_output_precision_1 (s stmt_vec_info use_stmt_info = vinfo->lookup_stmt (use_stmt); if (!use_stmt_info || !use_stmt_info->min_input_precision) return false; + /* The input precision recorded for COND_EXPRs applies only to the + "then" and "else" values. */ + gassign *assign = dyn_cast <gassign *> (stmt_info->stmt); + if (assign + && gimple_assign_rhs_code (assign) == COND_EXPR + && use->use != gimple_assign_rhs2_ptr (assign) + && use->use != gimple_assign_rhs3_ptr (assign)) + return false; precision = MAX (precision, use_stmt_info->min_input_precision); } Index: gcc/testsuite/gcc.dg/vect/pr86749.c =================================================================== --- /dev/null 2018-07-26 10:26:13.137955424 +0100 +++ gcc/testsuite/gcc.dg/vect/pr86749.c 2018-08-01 10:12:45.865913009 +0100 @@ -0,0 +1,26 @@ +/* { dg-additional-options "-O3" } */ + +#include "tree-vect.h" + +short a, b, f, g; +int c = 4, d, e = -1L; +long h = 4; + +int +main () +{ + check_vect (); + + long i; + for (; d <= 55; d++) + { + g = c >= 2 ? 0 : b << c; + f = g - a; + i = (f ^ 9223372036854775807) < 0 ? f : h; + e &= i; + } + if (e != 4) + __builtin_abort (); + + return 0; +}