Hi! On the following testcase we emit a bogus 'va_arg_tmp.5' may be used uninitialized warning. The reason is that when gimplifying the addr = &temp; statement, the va_arg_tmp temporary var for which we emit ADDR_EXPR is not TREE_ADDRESSABLE, prepare_gimple_addressable emits some extra code to initialize the newly addressable var from its previous value, but it is a new variable which hasn't been initialized yet and will be later, so we end up initializing it with uninitialized SSA_NAME: va_arg_tmp.6 = va_arg_tmp.5_14(D); addr.2_16 = &va_arg_tmp.6; _17 = MEM[(double *)sse_addr.4_13]; MEM[(double * {ref-all})addr.2_16] = _17; and with -O1 we actually don't DSE it before the warning is emitted. If we make the temp TREE_ADDRESSABLE before the gimplification, then this prepare_gimple_addressable path isn't taken and we effectively omit the first statement above and so the bogus warning is gone.
I went through other backends and didn't find another instance of this problem. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2022-04-22 Jakub Jelinek <ja...@redhat.com> PR target/105331 * config/i386/i386.cc (ix86_gimplify_va_arg): Mark va_arg_tmp temporary TREE_ADDRESSABLE before trying to gimplify ADDR_EXPR of it. * gcc.dg/pr105331.c: New test. --- gcc/config/i386/i386.cc.jj 2022-04-12 09:20:07.566662842 +0200 +++ gcc/config/i386/i386.cc 2022-04-21 12:03:32.201951522 +0200 @@ -4891,6 +4891,7 @@ ix86_gimplify_va_arg (tree valist, tree { int i, prev_size = 0; tree temp = create_tmp_var (type, "va_arg_tmp"); + TREE_ADDRESSABLE (temp) = 1; /* addr = &temp; */ t = build1 (ADDR_EXPR, build_pointer_type (type), temp); --- gcc/testsuite/gcc.dg/pr105331.c.jj 2022-04-21 12:09:34.398906718 +0200 +++ gcc/testsuite/gcc.dg/pr105331.c 2022-04-21 12:09:07.304283903 +0200 @@ -0,0 +1,11 @@ +/* PR target/105331 */ +/* { dg-do compile } */ +/* { dg-options "-O -Wuninitialized" } */ + +#include <stdarg.h> + +int +foo (va_list *va) +{ + return va_arg (*va, double _Complex); /* { dg-bogus "may be used uninitialized" } */ +} Jakub