<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/60860>60860</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Wasm] clang produces wrong code at -O targeting wasm32-unknown-emscripten
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Air111
      </td>
    </tr>
</table>

<pre>
    Hi,
I found emcc produce wrong code on this test case:

```c
#include <stdio.h>
#include <stdint.h>

union {
  uint64_t c;
  int32_t a;
} d;
int32_t a = 0;
int32_t e = 0;
uint64_t *f = &d.c;
static int32_t *g = &d.a;

int main() {
  for (; e <= 0; e++) {
    *f = 0x3b47c02bffe;
    for (; a; a++) {
      *g = 2;
    }
  }
 printf("%llx\n", d.c);
}
```

I reported this testcase to emscripten a few days ago(emscripten-core/emscripten#18767), and I think it may be clang bug.

**Version**
```shell
$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.31 (e88336121cfe6da4a96c88e46f314552f07dfed0)
clang version 17.0.0 (https://github.com/llvm/llvm-project 1142e6c7c795de7f80774325a07ed49bc95a48c9)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/x/emsdk/upstream/bin
$ /home/x/emsdk/upstream/bin/clang -v
clang version 17.0.0 (https://github.com/llvm/llvm-project 1142e6c7c795de7f80774325a07ed49bc95a48c9)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/x/emsdk/upstream/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ /home/x/emsdk/upstream/bin/wasm-ld -v
LLD 17.0.0
```

**Failing command line in full:**
```shell
$ /home/x/emsdk/upstream/bin/clang -target wasm32-unknown-emscripten -fignore-exceptions -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -DEMSCRIPTEN -Werror=implicit-function-declaration --sysroot=/home/x/emsdk/upstream/emscripten/cache/sysroot -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -Os small.c -c -o small.o
$ /home/x/emsdk/upstream/bin/wasm-ld -o small.wasm small.o -L/home/x/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten /home/x/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/crt1.o -lGL -lal -lhtml5 -lstandalonewasm -lstubs -lc -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --strip-debug --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export=stackSave --export=stackRestore --export=stackAlloc --export=__errno_location --export-table -z stack-size=65536 --initial-memory=16777216 --max-memory=16777216 --global-base=1024
$ wasmtime small.wasm
3b400000000
//only remove the "-Os" option
$ wasmtime small.wasm
3b47c02bffe
```

If this program contains undefined behaviour, I earnestly ask for your forgiveness.

Hope to get your reply.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzEWF9z27gR_zTQyw40JECR0oMebCm680x617lce33TgMBSQgwCGgC0pfv0HZDUHycXO2mT1qORhd3lD_sPu1iKEPTOIi7J7J7M1hPRxb3zyzvt8zyf1E6dlj9rwlYkW5Ps7gEa11kF2EoJB-9UJxGevbM7kE4hOAtxrwNEDBGkCEj43fDk-F1mw0eOa8a1laZTCISvQlTaTfeEv_sS18Zbdv_dWe0skOp-WAJ02say2EaQhF-I2kbOthHEhUaqNajL6sIHwteQfUbHT-iXTQi7a3oeYaWaXrcMUUQtL_sSdre7it1ocd4FWqEtYXPCFrfGNM5DovL7XoXVWQtAwu77zwtxuOqTHXldVDJjddPgjSdeYIrh66-h4Ko1ewFAqvV5cf158NrGpreAETYz5khmK9svVpA8wxa3vv8kH2698QAeD85HVNdkSrkE0QG2QXp9iGhBQIPPoMQpgNg5wuZXHpXOI2GbK4Uwns-rskpasBUIq-AhodtH0Mn3J6gRpBF2B3W3m77IWZY-_0QftLPD4hPlwx6NOQsXw-GgTwOhXxA2f3dVfCclYZt-M2r0IyZzjZDYok2Jcg9G20f0gG1nRNR2Bz_98g8wKgWIT_MpzxMgzueclznLZYOlEoVYlHI-x6JseF7MZqzJKtWgypLFvSaDdU-DHZBX02yaJaB9jIeQzinbELbZ6bjv6ql0LWEbY57O_-jBu48oI-R5wbCUlawWM4VVM8-qquBsJrIKVbGo5WImirlcXPb9XfgdRsLv4FmEljPa2Ufrni29ic4guPcoFLROoUniBxf0cUwJG6IwBtVa-8QibLN3bQrxcQizeiRs0x1C9CiSyrW214B8lfQYkUvg_v_uOs7LbVlc3GW07Y50Z7sf6K1NX92lsEorERF-Wq1AD2gipvQf0Lrgk526Th7os3nU9aoj28x-AOSUT_PvD1v9AMjpbJp9f9j594cc0-4DGpSp5H4HrNVFsbYzUaeH-B1MU_kvsrYsXpPibBTj7DWx40XueBa8WPDapt9QDlK1okZdCsL79-uxDLzSu4b-sBHa6P5O1Lap1RhtEbSFpjOmLx1vN5Fvq1mxLxpfLrBAG72zziPFo8RDimsA2jzpoGttdDwRvlbYiM5EoG0qYECla2tt0dOdcbUwVBgtAhVWmFPQgfB1I0zAizhaURu82ZOGj-bjha106PkmeKDrd3_7sPrt4e-_v_sF6B_ovfOEr3V7MFrqSJvOyqQiVSiN8H0aAqXhFLxzkfD1m865bfwbKeQ-yY7PA_3X6DX9rOP-jMo2412TsE0jHjEo8xWS0rUHEYH-GiC0wpipBCqBunHl_vOsO0MkwhkN6Pv_yvTLCR4T5SZBfhBukvUxT6qbn94DNcIANfvYmhlQE6KwShhnsbcyEbo6ADUSqFEmGe3Sz-RlbdBvfUyr4b5KrRuS-UoStb6lBicfMYb_RUbTEL0-UIV1twNK8ZgusFQ3VGGjLSrC19ttiMLHLbbb3tgvCrnD2zIjkNH1VuEhvIn2FYIj5Me3wW5ECF-HKOTjB_GEnxF_wxCd_5x-N4T1St1u0XvrtsbJ82EfNYjJxUD_hP5BGvSfSPi6nM14CZRqq6MWhrbYOp9qWF5WVcXyxGvF8S_pY-zrfjhd5xm76QwpC6Nu8eboDUxeF9n4d5ZOtz9nzQk8tu4JIe4RCGP010AYA9fX2K9Dvgxpr4xEzTAKHbzbedGCdDYKbQN0dgwQ1LgXT9p1Ps03D4DCWwzRnECEx37kO7nOpx87_YQWQ3gx5PzsDv18lbpIL5hmktN0opZcLfhCTHCZl1U5zxY8qyb7ZVXlSjVZXogZzhpczBdzzhdFxutKqFrWE71kGeMZyxc5Y3lRTWeqQJmXglUCc1VLUmTYCm2m6TRNnd9NdAgdLstsXmYTI2o0oX8pwZjFZ-iZaZqcrSd-2V-x624XSJEZHWK4okQdTf8244_k49l6nOrGlxXh9m1FX7hh6J2pXX-xfU46b5bfdvFPXSKpHAjb9Cb9OwAA__8Be3Vr">