[Bug c/109714] New: bogus may be used uninitialized warning

[Bug c/109714] New: bogus may be used uninitialized warning

[david at ixit dot cz]

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.

[Bug tree-optimization/109714] bogus "may be used uninitialized warning"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2023-05-03
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Can you attach the preprocessed source as requested on
https://gcc.gnu.org/bugs/ ?

[Bug tree-optimization/109714] bogus "may be used uninitialized warning"

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
This is likely a duplicate, the issue is that uninit diagnostics do not cope
well with loops and use/def predicates that eventually involve PHIs with
backedges.

[Bug tree-optimization/109714] bogus "may be used uninitialized warning"

[david at ixit dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #3 from David Heidelberg (okias) <david at ixit dot cz> ---
Created attachment 55000
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55000&action=edit
draw_draw_llvm.c.i.gz

[Bug tree-optimization/109714] bogus "may be used uninitialized warning"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |UNCONFIRMED
     Ever confirmed|1                           |0

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
What options are being used to compile this?
I cannot reproduce it on the trunk ...

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[david at ixit dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #5 from David Heidelberg (okias) <david at ixit dot cz> ---
Created attachment 55005
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55005&action=edit
meson-setup-output.txt

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
     Ever confirmed|0                           |1
   Last reconfirmed|2023-05-03 00:00:00         |2023-05-05

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to David Heidelberg (okias) from comment #5)
> Created attachment 55005 [details]
> meson-setup-output.txt

This does not enough information.
How is gcc invoked for compiling this?
You might be able to add --verbose to meson command line to see that. Otherwise
there is not much that can be done here.

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
That is how is gcc being invoked to create draw_draw_llvm.c.o .

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[david at ixit dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #8 from David Heidelberg (okias) <david at ixit dot cz> ---
Thank you for your patience with me!

ccache cc -Isrc/panfrost/vulkan/libvulkan_panfrost.so.p -Isrc/panfrost/vulkan
-I../src/panfrost/vulkan -Iinclude -I../include -Isrc -I../src -Isrc/compiler
-I../src/compiler -I../src/gallium/include -Isrc/gallium/auxiliary
-I../src/gallium/auxiliary -Isrc/panfrost -I../src/panfrost
-I../src/panfrost/include -Isrc/panfrost/shared -I../src/panfrost/shared
-Isrc/panfrost/midgard -I../src/panfrost/midgard -Isrc/panfrost/compiler
-I../src/panfrost/compiler -Isrc/panfrost/lib -I../src/panfrost/lib
-Isrc/compiler/nir -I../src/compiler/nir -Isrc/panfrost/lib/genxml
-I../src/panfrost/lib/genxml -Isrc/vulkan/util -I../src/vulkan/util
-Isrc/vulkan/runtime -I../src/vulkan/runtime -Isrc/vulkan/wsi
-I../src/vulkan/wsi -Isrc/egl/wayland/wayland-drm -I/usr/include/libdrm
-I/usr/include/valgrind -I/usr/include/x86_64-linux-gnu
-fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch
-std=c11 -O3 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS
-D__STDC_LIMIT_MACROS '-DPACKAGE_VERSION="23.2.0-devel"'
'-DPACKAGE_BUGREPORT="https://gitlab.freedesktop.org/mesa/mesa/-/issues"'
-DHAVE_OPENGL=1 -DHAVE_OPENGL_ES_1=1 -DHAVE_OPENGL_ES_2=1 -DHAVE_SWRAST
-DVIDEO_CODEC_VC1DEC=0 -DVIDEO_CODEC_H264DEC=1 -DVIDEO_CODEC_H264ENC=1
-DVIDEO_CODEC_H265DEC=1 -DVIDEO_CODEC_H265ENC=1 -DHAVE_X11_PLATFORM
-DHAVE_WAYLAND_PLATFORM -DHAVE_SURFACELESS_PLATFORM -DHAVE_DRM_PLATFORM
-DHAVE_XCB_PLATFORM -DENABLE_ST_OMX_BELLAGIO=0 -DENABLE_ST_OMX_TIZONIA=0
-DGLX_INDIRECT_RENDERING -DGLX_DIRECT_RENDERING -DGLX_USE_DRM -DALLOW_KCMP
-DENABLE_SHADER_CACHE -DHAVE___BUILTIN_BSWAP32 -DHAVE___BUILTIN_BSWAP64
-DHAVE___BUILTIN_CLZ -DHAVE___BUILTIN_CLZLL -DHAVE___BUILTIN_CTZ
-DHAVE___BUILTIN_EXPECT -DHAVE___BUILTIN_FFS -DHAVE___BUILTIN_FFSLL
-DHAVE___BUILTIN_POPCOUNT -DHAVE___BUILTIN_POPCOUNTLL
-DHAVE___BUILTIN_UNREACHABLE -DHAVE___BUILTIN_TYPES_COMPATIBLE_P
-DHAVE_FUNC_ATTRIBUTE_CONST -DHAVE_FUNC_ATTRIBUTE_FLATTEN
-DHAVE_FUNC_ATTRIBUTE_MALLOC -DHAVE_FUNC_ATTRIBUTE_PURE
-DHAVE_FUNC_ATTRIBUTE_UNUSED -DHAVE_FUNC_ATTRIBUTE_WARN_UNUSED_RESULT
-DHAVE_FUNC_ATTRIBUTE_WEAK -DHAVE_FUNC_ATTRIBUTE_FORMAT
-DHAVE_FUNC_ATTRIBUTE_PACKED -DHAVE_FUNC_ATTRIBUTE_RETURNS_NONNULL
-DHAVE_FUNC_ATTRIBUTE_ALIAS -DHAVE_FUNC_ATTRIBUTE_NORETURN
-DHAVE_FUNC_ATTRIBUTE_VISIBILITY -DHAVE_UINT128 -DHAVE_REALLOCARRAY
-DHAVE_FMEMOPEN -D_GNU_SOURCE -DUSE_SSE41 -DUSE_GCC_ATOMIC_BUILTINS
-DUSE_X86_64_ASM -DMAJOR_IN_SYSMACROS -DHAS_SCHED_H -DHAS_SCHED_GETAFFINITY
-DHAVE_LINUX_FUTEX_H -DHAVE_ENDIAN_H -DHAVE_DLFCN_H -DHAVE_SYS_SHM_H
-DHAVE_CET_H -DHAVE_SYS_INOTIFY_H -DHAVE_STRTOF -DHAVE_MKOSTEMP
-DHAVE_TIMESPEC_GET -DHAVE_MEMFD_CREATE -DHAVE_RANDOM_R -DHAVE_FLOCK
-DHAVE_STRTOK_R -DHAVE_GETRANDOM -DHAVE_POSIX_FALLOCATE -DHAVE_GNU_QSORT_R
-DHAVE_STRUCT_TIMESPEC -DHAVE_PROGRAM_INVOCATION_NAME -DHAVE_ISSIGNALING
-DHAVE_POSIX_MEMALIGN -DHAVE_DIRENT_D_TYPE -DHAVE_STRTOD_L -DHAVE_DLADDR
-DHAVE_DL_ITERATE_PHDR -DHAVE_ZLIB -DHAVE_ZSTD -DHAVE_COMPRESSION
-DHAVE_PTHREAD -DHAVE_PTHREAD_SETAFFINITY -DHAVE_LIBDRM -DHAVE_LIBUDEV
-DLLVM_AVAILABLE '-DMESA_LLVM_VERSION_STRING="14.0.6"' -DLLVM_IS_SHARED=1
-DDRAW_LLVM_AVAILABLE -DUSE_LIBELF -DHAVE_VALGRIND -DMESA_EXECMEM
-DHAVE_LIBUNWIND -DWL_HIDE_DEPRECATED -DHAVE_OPENMP -DHAVE_DRI -DHAVE_DRI2
-DHAVE_DRI3 -DHAVE_DRI3_MODIFIERS -DHAVE_DRISW_KMS -DHAVE_GALLIUM_EXTRA_HUD=1
-mtls-dialect=gnu2 -Werror=implicit-function-declaration
-Werror=missing-prototypes -Werror=return-type -Werror=empty-body
-Werror=incompatible-pointer-types -Werror=int-conversion
-Wimplicit-fallthrough -Wmisleading-indentation -Wno-missing-field-initializers
-Wno-format-truncation -Wno-nonnull-compare -fno-math-errno -fno-trapping-math
-fno-common -Wno-unused-function -Werror=format -Wformat-security
-ffunction-sections -fdata-sections -Wno-unused-variable
-Wno-unused-but-set-variable -save-temps -fPIC -DVK_USE_PLATFORM_XCB_KHR
-DVK_USE_PLATFORM_XLIB_KHR -DVK_USE_PLATFORM_WAYLAND_KHR
-DVK_USE_PLATFORM_DISPLAY_KHR -DVK_USE_PLATFORM_XLIB_XRANDR_EXT -pthread
-Wno-override-init -MD -MQ
src/panfrost/vulkan/libvulkan_panfrost.so.p/panvk_cmd_buffer.c.o -MF
src/panfrost/vulkan/libvulkan_panfrost.so.p/panvk_cmd_buffer.c.o.d -o
src/panfrost/vulkan/libvulkan_panfrost.so.p/panvk_cmd_buffer.c.o -c
../src/panfrost/vulkan/panvk_cmd_buffer.c

[Bug tree-optimization/109714] mesa/aux/draw_llvm: bogus "may be used uninitialized warning"

[david at ixit dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109714

--- Comment #9 from David Heidelberg (okias) <david at ixit dot cz> ---
Sorry, the previous command was for different bug (bugzilla weirdly switching
bugs when sending the comment, probably disabled JS :/ )

Here it's:

/usr/lib/gcc-snapshot/bin/gcc -Isrc/gallium/auxiliary/libgallium.a.p
-Isrc/gallium/auxiliary -I../src/gallium/auxiliary -Isrc/loader -I../src/loader
-I../src/gallium/include -Isrc -I../src -Iinclude -I../include
-I../src/gallium/auxiliary/util -Isrc/compiler/nir -I../src/compiler/nir
-I/usr/include/libdrm -I/usr/include/valgrind -I/usr/include/x86_64-linux-gnu
-fvisibility=hidden -fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64
-Wall -Winvalid-pch -std=c11 -O3 '-DPACKAGE_VERSION="23.2.0-devel"'
'-DPACKAGE_BUGREPORT="https://gitlab.freedesktop.org/mesa/mesa/-/issues"'
-DHAVE_OPENGL=1 -DHAVE_OPENGL_ES_1=1 -DHAVE_OPENGL_ES_2=1 -DHAVE_R300
-DHAVE_I915 -DHAVE_IRIS -DHAVE_SWRAST -DVIDEO_CODEC_VC1DEC=0
-DVIDEO_CODEC_H264DEC=1 -DVIDEO_CODEC_H264ENC=1 -DVIDEO_CODEC_H265DEC=1
-DVIDEO_CODEC_H265ENC=1 -DHAVE_X11_PLATFORM -DHAVE_WAYLAND_PLATFORM
-DHAVE_SURFACELESS_PLATFORM -DHAVE_DRM_PLATFORM -DHAVE_XCB_PLATFORM
-DENABLE_ST_OMX_BELLAGIO=0 -DENABLE_ST_OMX_TIZONIA=0 -DGLX_INDIRECT_RENDERING
-DGLX_DIRECT_RENDERING -DGLX_USE_DRM -DALLOW_KCMP -DENABLE_SHADER_CACHE
-DHAVE___BUILTIN_BSWAP32 -DHAVE___BUILTIN_BSWAP64 -DHAVE___BUILTIN_CLZ
-DHAVE___BUILTIN_CLZLL -DHAVE___BUILTIN_CTZ -DHAVE___BUILTIN_EXPECT
-DHAVE___BUILTIN_FFS -DHAVE___BUILTIN_FFSLL -DHAVE___BUILTIN_POPCOUNT
-DHAVE___BUILTIN_POPCOUNTLL -DHAVE___BUILTIN_UNREACHABLE
-DHAVE___BUILTIN_TYPES_COMPATIBLE_P -DHAVE_FUNC_ATTRIBUTE_CONST
-DHAVE_FUNC_ATTRIBUTE_FLATTEN -DHAVE_FUNC_ATTRIBUTE_MALLOC
-DHAVE_FUNC_ATTRIBUTE_PURE -DHAVE_FUNC_ATTRIBUTE_UNUSED
-DHAVE_FUNC_ATTRIBUTE_WARN_UNUSED_RESULT -DHAVE_FUNC_ATTRIBUTE_WEAK
-DHAVE_FUNC_ATTRIBUTE_FORMAT -DHAVE_FUNC_ATTRIBUTE_PACKED
-DHAVE_FUNC_ATTRIBUTE_RETURNS_NONNULL -DHAVE_FUNC_ATTRIBUTE_ALIAS
-DHAVE_FUNC_ATTRIBUTE_NORETURN -DHAVE_FUNC_ATTRIBUTE_VISIBILITY -DHAVE_UINT128
-DHAVE_REALLOCARRAY -DHAVE_FMEMOPEN -DUSE_SSE41 -DUSE_GCC_ATOMIC_BUILTINS
-DUSE_X86_64_ASM -DMAJOR_IN_SYSMACROS -DHAS_SCHED_H -DHAS_SCHED_GETAFFINITY
-DHAVE_LINUX_FUTEX_H -DHAVE_ENDIAN_H -DHAVE_DLFCN_H -DHAVE_SYS_SHM_H
-DHAVE_CET_H -DHAVE_SYS_INOTIFY_H -DHAVE_STRTOF -DHAVE_MKOSTEMP
-DHAVE_TIMESPEC_GET -DHAVE_MEMFD_CREATE -DHAVE_RANDOM_R -DHAVE_FLOCK
-DHAVE_STRTOK_R -DHAVE_GETRANDOM -DHAVE_POSIX_FALLOCATE -DHAVE_GNU_QSORT_R
-DHAVE_STRUCT_TIMESPEC -DHAVE_PROGRAM_INVOCATION_NAME -DHAVE_ISSIGNALING
-DHAVE_POSIX_MEMALIGN -DHAVE_DIRENT_D_TYPE -DHAVE_STRTOD_L -DHAVE_DLADDR
-DHAVE_DL_ITERATE_PHDR -DSUPPORT_INTEL_INTEGRATED_GPUS -DHAVE_ZLIB -DHAVE_ZSTD
-DHAVE_COMPRESSION -DHAVE_PTHREAD -DHAVE_PTHREAD_SETAFFINITY -DHAVE_LIBDRM
-DHAVE_LIBUDEV -DLLVM_AVAILABLE '-DMESA_LLVM_VERSION_STRING="14.0.6"'
-DLLVM_IS_SHARED=1 -DDRAW_LLVM_AVAILABLE -DUSE_LIBELF -DHAVE_VALGRIND
-DMESA_EXECMEM -DHAVE_LIBUNWIND -DWL_HIDE_DEPRECATED -DHAVE_OPENMP -DHAVE_DRI
-DHAVE_DRI2 -DHAVE_DRI3 -DHAVE_DRI3_MODIFIERS -DHAVE_DRISW_KMS
-DHAVE_GALLIUM_EXTRA_HUD=1 -mtls-dialect=gnu2
-Werror=implicit-function-declaration -Werror=missing-prototypes
-Werror=return-type -Werror=empty-body -Werror=incompatible-pointer-types
-Werror=int-conversion -Wimplicit-fallthrough -Wmisleading-indentation
-Wno-missing-field-initializers -Wno-format-truncation -Wno-nonnull-compare
-fno-math-errno -fno-trapping-math -fno-common -Wno-unused-function
-Werror=format -Wformat-security -ffunction-sections -fdata-sections
-Wno-unused-variable -Wno-unused-but-set-variable -save-temps -fPIC -pthread
-isystem/usr/lib/llvm-14/include -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS
-D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Werror=pointer-arith -Werror=vla
-MD -MQ src/gallium/auxiliary/libgallium.a.p/draw_draw_llvm.c.o -MF
src/gallium/auxiliary/libgallium.a.p/draw_draw_llvm.c.o.d -o
src/gallium/auxiliary/libgallium.a.p/draw_draw_llvm.c.o -c
../src/gallium/auxiliary/draw/draw_llvm.c