https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714
Bug ID: 109714
Summary: bogus may be used uninitialized warning
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: david at ixit dot cz
Target Milestone: ---
Host: x86_64
Target: x86_64
Code: https://gitlab.freedesktop.org/mesa/mesa/ main branch
Compiler: 13.0.1 20230315 (experimental) [master r13-6680-ga9ae16db8cb]
Compilation:
```
CC=/usr/lib/gcc-snapshot/bin/gcc CXX=/usr/lib/gcc-snapshot/bin/g++ meson setup
builddir-snapshot -D libdir=lib -D buildtype=release -D build-tests=false -D
enable-glcpp-tests=false -D libunwind=enabled -D glx=dri -D gbm=enabled -D
egl=enabled -D platforms=x11,wayland -D dri3=enabled -D gallium-extra-hud=true
-D gallium-vdpau=disabled -D gallium-omx=disabled -D gallium-va=disabled -D
gallium-xa=disabled -D gallium-nine=false -D gallium-opencl=disabled -D
gallium-rusticl=false -D llvm=enabled -D gallium-drivers=i915,iris,swrast -D
vulkan-drivers= -D video-codecs=h264dec,h264enc,h265dec,h265enc -D
spirv-to-dxil=false -D osmesa=true -D intel-clc=disabled -D
imagination-srv=false
```
```
[1110/1401] Compiling C object
src/gallium/auxiliary/libgallium.a.p/draw_draw_llvm.c.o
In function 'generate_clipmask',
inlined from 'draw_llvm_generate' at
../src/gallium/auxiliary/draw/draw_llvm.c:2163:24:
../src/gallium/auxiliary/draw/draw_llvm.c:1496:25: warning: 'sum' may be used
uninitialized [-Wmaybe-uninitialized]
1496 | sum = lp_build_fmuladd(builder, planes,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1497 | (LLVMValueRef[]){cv_x, cv_y,
cv_z, cv_w}[i], sum);
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/gallium/auxiliary/draw/draw_llvm.c: In function 'draw_llvm_generate':
../src/gallium/auxiliary/draw/draw_llvm.c:1343:44: note: 'sum' was declared
here
1343 | LLVMValueRef plane1, planes, plane_ptr, sum;
|
```
The code (relevant to the sum variable):
```
...
LLVMValueRef plane1, planes, plane_ptr, sum;
...
for (int i = 0; i < 4; ++i) {
indices[2] = lp_build_const_int32(gallivm, i);
plane_ptr = LLVMBuildGEP2(builder, planes_type, planes_ptr,
indices, 3, "");
plane1 = LLVMBuildLoad2(builder, vs_elem_type, plane_ptr,
(const char *[]){"plane_x", "plane_y",
"plane_z", "plane_w"}[i]);
planes = lp_build_broadcast(gallivm, vs_type_llvm, plane1);
if (i == 0) {
sum = LLVMBuildFMul(builder, planes, cv_x, ""); // sum is set
always in first iteration
} else {
// we never get here without having sum already assigned
sum = lp_build_fmuladd(builder, planes,
(LLVMValueRef[]){cv_x, cv_y, cv_z,
cv_w}[i], sum);
}
}
...
```
Thou the `sum` value is always assigned in first for interation.
I tried do simple test case, but it always works with simple c file.
