<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/113803>113803</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang-20 : Assertion `!DT.isNull() && "Undeduced types shouldn't reach here."' failed.
        </td>
    </tr>

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

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

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

<pre>
    ### Description
I encountered a crash in Clang-20 when compiling the following code snippet:

```cpp
 char myfunc();
 
 template<typename T> T my_templated_func();
 
 template<> auto my_templated_func()
 {
   return myfunc();
 }

```

###  Error Message
The compilation fails with the following assertion error:
```sh
clang++: /root/llvm-project/clang/lib/CodeGen/CGDebugInfo.cpp:3681: clang::QualType UnwrapTypeForDebugInfo(clang::QualType, const clang::ASTContext&): Assertion !DT.isNull() && "Undeduced types shouldn't reach here." failed.

```

### Command
```sh
clang++ bug.cpp -O3 -ffast-math -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address -c -o bug.o

clang++: /root/llvm-project/clang/lib/CodeGen/CGDebugInfo.cpp:3681: clang::QualType UnwrapTypeForDebugInfo(clang::QualType, const clang::ASTContext&): Assertion `!DT.isNull() && "Undeduced types shouldn't reach here."' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -O3 -ffast-math -Wall -Wextra -fno-strict-aliasing -fwrapv -g -fsanitize=address <source>
1.      <eof> parser at end of file
2.      <source>:5:18: LLVM IR generation of declaration 'my_templated_func'
3.      <source>:5:18: Generating code for declaration 'my_templated_func'
 #0 0x0000000003bd52c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bd52c8)
 #1 0x0000000003bd2fcc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bd2fcc)
 #2 0x0000000003b209a8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007032d0e42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007032d0e969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007032d0e42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007032d0e287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007032d0e2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007032d0e39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000003e86e5b UnwrapTypeForDebugInfo(clang::QualType, clang::ASTContext const&) CGDebugInfo.cpp:0:0
#10 0x0000000003ecf54c clang::CodeGen::CGDebugInfo::getOrCreateType(clang::QualType, llvm::DIFile*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ecf54c)
#11 0x0000000003ed5a01 clang::CodeGen::CGDebugInfo::CollectTemplateParams(std::optional<clang::CodeGen::CGDebugInfo::TemplateArgs>, llvm::DIFile*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ed5a01)
#12 0x0000000003ee2be2 clang::CodeGen::CGDebugInfo::collectFunctionDeclProps(clang::GlobalDecl, llvm::DIFile*, llvm::StringRef&, llvm::StringRef&, llvm::DIScope*&, llvm::MDTupleTypedArrayWrapper<llvm::DINode>&, llvm::DINode::DIFlags&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ee2be2)
#13 0x0000000003ee3667 clang::CodeGen::CGDebugInfo::emitFunctionStart(clang::GlobalDecl, clang::SourceLocation, clang::SourceLocation, clang::QualType, llvm::Function*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ee3667)
#14 0x0000000003fb4bd6 clang::CodeGen::CodeGenFunction::StartFunction(clang::GlobalDecl, clang::QualType, llvm::Function*, clang::CodeGen::CGFunctionInfo const&, clang::CodeGen::FunctionArgList const&, clang::SourceLocation, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fb4bd6)
#15 0x0000000003fba589 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3fba589)
#16 0x00000000040230aa clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x40230aa)
#17 0x000000000401dfd5 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x401dfd5)
#18 0x000000000401e3bb clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x401e3bb)
#19 0x00000000040287b3 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#20 0x000000000454d106 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#21 0x000000000453de38 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x453de38)
#22 0x00000000066a1884 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66a1884)
#23 0x000000000454acb8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x454acb8)
#24 0x00000000048045d9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48045d9)
#25 0x00000000047837be clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47837be)
#26 0x00000000048e9cee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48e9cee)
#27 0x0000000000ce2b8f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce2b8f)
#28 0x0000000000cda84a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#29 0x000000000458e0c9 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#30 0x0000000003b20e54 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b20e54)
#31 0x000000000458e6bf clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#32 0x000000000455487d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x455487d)
#33 0x000000000455596d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x455596d)
#34 0x000000000455cd25 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x455cd25)
#35 0x0000000000cdfa29 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdfa29)
#36 0x0000000000baddb4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbaddb4)
#37 0x00007032d0e29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#38 0x00007032d0e29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#39 0x0000000000cda2fe _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcda2fe)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```


The issue can also be reproduced on Compiler Explorer: https://godbolt.org/z/r9hhKz8zq
### Steps to Reproduce:

Compile the provided code snippet using Clang-20.
Observe the crash and assertion failure.

###  Additional Information
Please let me know if you need any more details.

Thank you for your assistance.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWt1y2ziyfhr6BkUVCVIUdeELRbJzPCeZ5MSemUsVCDQlHoMAFwD9k6ffAkDJhCJ57Kyd2tqd0sQSfhpff91oNMgmWjcbAXAeTT9E09UZ6c1WqvOGtERI8djKXlN9Vkn2eB7hzH_QCjRVTWcaKaJkFSWLKwSCyl4YUMAQQVQRvUWNQEtOxCbGCbrfgkBUtl3DG7FBZguolpzLe_uLSgZIi6brwETZwssc_i0S_6Fd51sQ3RKF2se6FzTCZYTnUfZh6Br-GGg7TgxE2dI8diBIC-gmyi7QDWof17tetn6ZCDuR9EaenDtMnO1EIKTA9EqcAjlbHdUwaNxzjS6Ukgp9Bq3JBnzvzRYGLom1AapJwzW6b8z2gFiiNSg3BKyUJ253a-qtb6DWThH-YD_ZAkX4UklpInzJ-V0bd0r-P1D7cxh3yZsqwpdLyeAjCPvt4wqqfnMlajmxlsoWWVGmVpSfkS2ibPF_PeE3jx2gP8S9Ip39einVfmKEyyODI7xEVAptxpIW1zdLKQw8mAgXjtwFWux1jXC6upk0-veec08-csMKFGH8h2DAegoMWdfQSG9lz5mI8MwgBYRu0RYUTCKMHa3AJq8w1lK2LRHs70lGVb-xRKH4S4biuibaxC0xWxT_RThH8V_wYBRBcS1krI1qqIkJb4i2Ro1ry94diu1XTURjmu8QZSvCmAKtUUxRLN0CcozyP8vERfJGVo7wLDT0108Xi-sLpPuqbQwilkikoJPKICPR1phOW4T4MsKXm8Zs-2pCZTvw-COdjdY96AhfIiIYagTlPQO3TX2QrAi9NYpQx0KnoFOSgtbAkJa98s12JtFa0saGHqR6gXwAHiBfG0JvEevbbr_Dk0mUzL8quVGkRURt-haE0YPhZecM7SIIqBgeOi4VqJ3x433Y0LFRvbiN8GXViCffcB4cb9g9UXWcO0eUVi7pOiu9N11vJhrFreUCxfFDWcREt7F-FIY8RNmqEQa49-47UJXUYPtRfI3ieENpbKTkdEsaEWWrZ_HawVqQTm-lQXFNJZcqZg3ZCKlNQ7VfwzEdNr_9touy5WCx7MLbILU2iLIlyNqeIR1RGhQiBoFgSNaobvgQ0PEw8klAtphG2SItrcU-ffrzM7r6hjYgQPmIL2vEgHIy_Izw7MjhNPPCs2eFfxyE7o7hWqqXi0YRzhKUPCS7_7KKTTEtkdsLbh_rR-2_fFWNMM5Tb7y7l0-DFLlfS20UkNbt4SVqhPE7unwjf43wh-RhgDc6tHGWHuDHNaXH8C85ENF3X8R1sxHEhpxeuNyJIS7tKu-B1oIJ0OIQLU7mpERL69_fgMo7UI8e3v8QwbhdtByYDMYMkXWI44n7f79ENiwxSzLMEsjxFCeDav5MeCiLdZHHvBH9Q7wRve-gEy0nhQPupgSw81DmvJjXFHVmq4Cw9W3D-esWcPODBaaHoPNZgTbacfFa8PmsCGQXoWxczuoMkcqeCK-S7CYGkmc_SE6rV8tMq0BmGcrM5jAvXifTTQlkzgOvg7KAafX6I_7Y4e4Pfn_Eox9TjJFr2q0axhqg9TSnY7m7bMX_eJLmGzZgvqilAmLAYzqF9Gn3r64ubZDGi_fY3h7_nmirYBiMgE1Jkr5cwaXkHKi5GYL1V6JIqyNcasP8AOnubIRH2fLFQnfSFmqj7eHxC_lx6gf8hOEPAFeAX84P9fxc9oJaACug_KuSnQ494SOXFeG286Su4-Zroxqx-Qb1cHK9pGd1dU1l52UddH1e3fQddw7KFkqRx78U6TpQUbYcz_9dMneU_yjZ9wyAOdnoYXO9uXUc-YF1sgPrZEUxe7l1oG32prk2RJnnzDLquHZ5zSdJXcLyms7je36HYbB0JSV_H_4sPQF_ecBfXeUVK07z53_s0Q4uR5R5UuBF_L2IhdNW3A20hhxF89NTdhMWavOp0ebUnFeZ9e3N49kPzDM9MA-ZlvPXmWdItsF2vizo_KtmeA9irN4BMcWYmDzBWULI3xHzWbKeD4Hqom2MJ-ApNNeNvWE978RPNPn2Pwnv3-kwGrQK1J6FaqesZtOfU_vfUF2nTaBueaAuZFX1c-qeVvI9FLE4A0XmB-5azqrstYrcyO4T3MEAe6yOb9kZZdIRZSaJy27Hko7mtzjIb_NpztLE5e77Z_FIkBZ05-7P8wCgjStSXbUd983-Avg8zI9K9p3LT-bIw_rQN5yBOo4uDdFlDLJyzNsHQm9BsKUUum9B_RyOt7a_hzm2Pw6SyKIgaVnmYz2-EqVhcX0TAr2GlgynlE8J3i01GCAFmLMDzyC0Ko_47GJ02Fw8AO0NLHa5wLuw64AESIMkJi-TfMqCU_JS2ZufYEegvhNIjyEAGRzl-azMZhWEdPplr4Q2RFA4zuhprd7l6B1wBoqER28JcwqBIgPkJ33u9jlT-Zy-73OqeHyBAsEhmlDAVVkjStN1S6yM0UNCdxuyUSJbuleAQ5KzGC6lYRteojvZsPfRw6MM1ChDNRgpc4J25C_TGxcpRspct4TzP4HuY_YRnQ6udlbGsacmTDV3p0J2eNRNS0jo3BEzklsPOddaOW5d7-6d5cVwcSacV4TermsRPjrwaw8-tEx3778ONvVRGx57KHHs7mwxOAPvJ6zX9OEhTf2PiuiGrrUbPrAYDLYNa6NIY_Su-0Ac4dzuCalG_XbI6PbnnMhz7qZEeMZJWzES4dkTVbjcPQj-TVZH7XH4sBwnMM1Hpjj2kNb3fOvFNamBPwZ0Pm-693gi7RCPPT9LD12sqGr03-wiB2nfSV_AIXHTvJyxk8Q9ve0_jOuOzSCYH0y0A05dsp8ZugiSnZFub5tAOLUDhzpIdabTefFqXn6TlT5Nym-y-uHJw3Ohee8HHWmsC7hXKi_ncXCWX8KmJStgMz9gkzI8PYV8NfoeJA5HMoZTVviFbL5DOuvoCfibHhzsNcFDOrvLUHb4XVhZ_PB8-NSx_dY5iUMWQA9yw6QijFU5sqDfem0vOlj78M3WnM1f-RLRTQlklocyIU_Qem2nrbUhyqxHyr14FcjDVeaHmRyuAXn5b28zK3y_-kGFzq5ky3sbqocbBqLDjvBVK77sCx4a49_fp1luYfYaUHyHjEQaADWjtH9YbJfxD7VqYPeknfxcndO--MwVtSBKBCJcS1QBcoUrvuJGCrQXfrHjJlscls5IVkluJlJtInz5PcKXar7d_u_38vs_Dquqrg102qrybbdIFBYJDsu5qppOybuGAQuKClHvSjh21YhD2cyXSoO6GxfjDIU2Q5GRJbhXMDlRmLdgrPFpCboStVQteSqI_MqBaEAcDGoB3Qp5j5oaPcoeCQCGiHhErVSAGBjScD0JCSbi1o2tpbJ_lcXU-IvZ5IydZ2yezckZnKezLEmypEyzs-15UtezOk8rXCUZnbK6rudFVaZJUU0rQmb1WXOOE5ynCZ6lOCmm2aQqpiVLp2nNiinQWR7lCbSk4RMbvKxhzpydz9M0K5PsjJMKuHaFohgLuPdeEGEcTVdn6tzVPVX9Rkd5whtt9JMY0xgO5_ta0F9QynXWK37-87Vag8Z35_ifAQAA___jDjEz">