https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78646
Bug ID: 78646
Summary: incorrect result type for pointer addition in slsr
Product: gcc
Version: 5.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: stefan at reservoir dot com
Target Milestone: ---
Created attachment 40225
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40225&action=edit
output of -fdump-tree-slsr
In the program below, struct A is 64-bit aligned and struct B is 128-bit
aligned. An array of struct A in part of struct B.
When the array in B is accessed with a variable index, slsr computes the
pointer to the array element with the incorrect type 'struct B *' rather than
'struct A *'.
On my out-of-tree target, this results in incorrect code being generated; on
x86 I can only show the issue when looking at the debug output.
In the attached dump, the type of _8 and _14 is 'struct B *' but I would expect
them to have type 'struct A *'.
Here is the preprocessed program:
# 1 "bug.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "bug.cpp"
typedef int v4si __attribute__((vector_size(16)));
typedef int v2si __attribute__((vector_size(8)));
int __builtin_foo(int, int, int);
template <typename, typename> struct A;
template <> struct alignas(v2si) A<int, int> {
int _a;
int _b;
};
template <typename T> T foo(T a, A<int, int> &b, int) {
return __builtin_foo(a, b._a, b._b);
}
template <typename T> T foo(A<int, int> &a, T b, int c) {
return foo(b, a, c);
}
struct alignas(v4si) B {
struct {
A<int, int> ara[16];
};
int bar(int, int);
};
int B::bar(int i, int a) {
return foo(ara[i], a, 1);
}
Compiled using:
g++ -v -save-temps -Wall -Wextra -std=gnu++14 -fdump-tree-slsr
-fdump-tree-optimized -O -S bug.ii
Using built-in specs.
COLLECT_GCC=g++
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.4.0-6ubuntu1~16.04.4' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-i386/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-i386
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-i386
--with-arch-directory=i386 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-targets=all --enable-multiarch --disable-werror
--with-arch-32=i686 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=i686-linux-gnu
--host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=gnu++14'
'-fdump-tree-slsr' '-fdump-tree-optimized' '-O' '-S' '-shared-libgcc'
'-mtune=generic' '-march=i686'
/usr/lib/gcc/i686-linux-gnu/5/cc1plus -fpreprocessed bug.ii -quiet -dumpbase
bug.ii -mtune=generic -march=i686 -auxbase bug -O -Wall -Wextra -std=gnu++14
-version -fdump-tree-slsr -fdump-tree-optimized -o bug.s
-fstack-protector-strong -Wformat-security
GNU C++14 (Ubuntu 5.4.0-6ubuntu1~16.04.4) version 5.4.0 20160609
(i686-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (Ubuntu 5.4.0-6ubuntu1~16.04.4) version 5.4.0 20160609
(i686-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 427d6507e583781294a191f5962a1495
COMPILER_PATH=/usr/lib/gcc/i686-linux-gnu/5/:/usr/lib/gcc/i686-linux-gnu/5/:/usr/lib/gcc/i686-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/5/:/usr/lib/gcc/i686-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-linux-gnu/5/:/usr/lib/gcc/i686-linux-gnu/5/../../../i386-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/5/../../../../lib/:/lib/i386-linux-gnu/:/lib/../lib/:/usr/lib/i386-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/i686-linux-gnu/5/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=gnu++14'
'-fdump-tree-slsr' '-fdump-tree-optimized' '-O' '-S' '-shared-libgcc'
'-mtune=generic' '-march=i686'
Here is a possible solution for this problem (the assert is presumably
gratuitous):
diff --git a/gcc/gimple-ssa-strength-reduction.c
b/gcc/gimple-ssa-strength-reduction.c
--- a/gcc/gimple-ssa-strength-reduction.c
+++ b/gcc/gimple-ssa-strength-reduction.c
@@ -1918,7 +1918,9 @@ replace_ref (tree *expr, slsr_cand_t c)
if (align < TYPE_ALIGN (acc_type))
acc_type = build_aligned_type (acc_type, align);
- add_expr = fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (c->base_expr),
+ gcc_assert (POINTER_TYPE_P (c->cand_type));
+ add_expr = fold_build2 (POINTER_PLUS_EXPR,
+ build_pointer_type (TREE_TYPE (c->cand_type)),
c->base_expr, c->stride);
mem_ref = fold_build2 (MEM_REF, acc_type, add_expr,
wide_int_to_tree (c->cand_type, c->index));
