Clang CodeGenPrepare asserts building llvmlibc with LLVM_ENABLE_EXPENSIVE_CHECKS=ON

**What code / commands /steps will reproduce the problem?**
1. Download LLVM based Arm Toolchain for Embedded: https://github.com/arm/arm-toolchain.git
2. Compile it as 2-stage pipeline.
3. Compile with LLVM_ENABLE_EXPENSIVE_CHECKS=ON ; LLVM_ENABLE_ASSERTIONS=ON ; CMAKE_BUILD_TYPE=Debug

**What is the expected result?**
Compilation should be successful.

**What happens instead?**
Build aborts with `Pass modifies its input and doesn't report it: CodeGen Prepare` while compiling `libc/src/math/generic/sincos.cpp` and `cos.cpp`.

Stack traces point to `llvm/lib/IR/LegacyPassManager.cpp:1404`

Detailed logs:
```
[10/40] Performing build step for 'llvmlibc'
[775/1015] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj
FAILED: libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj
/home/ubuntu/arm-toolchain/build_assertions/llvm/bin/clang++ --target=aarch64-none-elf -DLIBC_NAMESPACE=__llvm_libc_23_0_0_git -I/home/ubuntu/arm-toolchain/libc -isystem /home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/llvmlibc/aarch64a_exn_rtti_unaligned/build/libc/include --target=aarch64-none-elf -march=armv8-a -fPIC -ffixed-x18 --sysroot /home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/runtimes/aarch64a_exn_rtti_unaligned/build/tmp_install -I/home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/runtimes/aarch64a_exn_rtti_unaligned/build/tmp_install/include -ffunction-sections -fdata-sections -fno-ident -Wno-error=atomic-alignment -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported -ffunction-sections -fdata-sections -Xclang -fno-pch-timestamp -O3 -DNDEBUG --target=aarch64-none-elf -D__LIBC_USE_BUILTIN_CEIL_FLOOR_RINT_TRUNC -D__LIBC_USE_BUILTIN_ROUND -D__LIBC_USE_BUILTIN_ROUNDEVEN -DLIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE -DLIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH -DLIBC_QSORT_IMPL=LIBC_QSORT_HEAP_SORT -DLIBC_COPT_STRING_LENGTH_IMPL=element -DLIBC_COPT_FIND_FIRST_CHARACTER_IMPL=element "-DLIBC_MATH=(LIBC_MATH_SKIP_ACCURATE_PASS | LIBC_MATH_SMALL_TABLES | LIBC_MATH_NO_ERRNO | LIBC_MATH_NO_EXCEPT | LIBC_MATH_INTERMEDIATE_COMP_IN_FLOAT)" -fno-math-errno -DLIBC_ERRNO_MODE=LIBC_ERRNO_MODE_SHARED -DLIBC_THREAD_MODE=LIBC_THREAD_MODE_SINGLE -DLIBC_CONF_WCTYPE_MODE=LIBC_WCTYPE_MODE_ASCII -DLIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT=100 -DLIBC_COPT_CTYPE_SMALLER_ASCII -DLIBC_COPT_PRINTF_DISABLE_WIDE -DLIBC_COPT_PRINTF_DISABLE_BITINT -DLIBC_TARGET_OS_IS_BAREMETAL -fpie -ffreestanding -DLIBC_FULL_BUILD -nostdlibinc -ffixed-point -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_COPT_PUBLIC_PACKAGING -MD -MT libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj -MF libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj.d -o libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj -c /home/ubuntu/arm-toolchain/libc/src/math/generic/sincos.cpp
Pass modifies its input and doesn't report it: CodeGen Prepare
Pass modifies its input and doesn't report it
UNREACHABLE executed at /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:1404!
PLEASE submit a bug report to https://github.com/arm/arm-toolchain/issues and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /home/ubuntu/arm-toolchain/build_assertions/llvm/bin/clang++ --target=aarch64-none-elf -DLIBC_NAMESPACE=__llvm_libc_23_0_0_git -I/home/ubuntu/arm-toolchain/libc -isystem /home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/llvmlibc/aarch64a_exn_rtti_unaligned/build/libc/include --target=aarch64-none-elf -march=armv8-a -fPIC -ffixed-x18 --sysroot /home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/runtimes/aarch64a_exn_rtti_unaligned/build/tmp_install -I/home/ubuntu/arm-toolchain/build_assertions/multilib-llvmlibc-builds/runtimes/aarch64a_exn_rtti_unaligned/build/tmp_install/include -ffunction-sections -fdata-sections -fno-ident -Wno-error=atomic-alignment -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported -ffunction-sections -fdata-sections -Xclang -fno-pch-timestamp -O3 -DNDEBUG --target=aarch64-none-elf -D__LIBC_USE_BUILTIN_CEIL_FLOOR_RINT_TRUNC -D__LIBC_USE_BUILTIN_ROUND -D__LIBC_USE_BUILTIN_ROUNDEVEN -DLIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE -DLIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH -DLIBC_QSORT_IMPL=LIBC_QSORT_HEAP_SORT -DLIBC_COPT_STRING_LENGTH_IMPL=element -DLIBC_COPT_FIND_FIRST_CHARACTER_IMPL=element "-DLIBC_MATH=(LIBC_MATH_SKIP_ACCURATE_PASS | LIBC_MATH_SMALL_TABLES | LIBC_MATH_NO_ERRNO | LIBC_MATH_NO_EXCEPT | LIBC_MATH_INTERMEDIATE_COMP_IN_FLOAT)" -fno-math-errno -DLIBC_ERRNO_MODE=LIBC_ERRNO_MODE_SHARED -DLIBC_THREAD_MODE=LIBC_THREAD_MODE_SINGLE -DLIBC_CONF_WCTYPE_MODE=LIBC_WCTYPE_MODE_ASCII -DLIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT=100 -DLIBC_COPT_CTYPE_SMALLER_ASCII -DLIBC_COPT_PRINTF_DISABLE_WIDE -DLIBC_COPT_PRINTF_DISABLE_BITINT -DLIBC_TARGET_OS_IS_BAREMETAL -fpie -ffreestanding -DLIBC_FULL_BUILD -nostdlibinc -ffixed-point -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_COPT_PUBLIC_PACKAGING -MD -MT libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj -MF libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj.d -o libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.obj -c /home/ubuntu/arm-toolchain/libc/src/math/generic/sincos.cpp
1. parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module '/home/ubuntu/arm-toolchain/libc/src/math/generic/sincos.cpp'.
4. Running pass 'CodeGen Prepare' on function '@_ZN22__llvm_libc_23_0_0_git4math6sincosEdPdS1_'
#0 0x0000ab544db9ab68 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/ubuntu/arm-toolchain/llvm/lib/Support/Unix/Signals.inc:880:11
#1 0x0000ab544db9b084 PrintStackTraceSignalHandler(void*) /home/ubuntu/arm-toolchain/llvm/lib/Support/Unix/Signals.inc:962:1
#2 0x0000ab544db992ac llvm::sys::RunSignalHandlers() /home/ubuntu/arm-toolchain/llvm/lib/Support/Signals.cpp:108:5
#3 0x0000ab544db9a41c llvm::sys::CleanupOnSignal(unsigned long) /home/ubuntu/arm-toolchain/llvm/lib/Support/Unix/Signals.inc:396:1
#4 0x0000ab544daad750 (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) /home/ubuntu/arm-toolchain/llvm/lib/Support/CrashRecoveryContext.cpp:71:7
#5 0x0000ab544daadb8c CrashRecoverySignalHandler(int) /home/ubuntu/arm-toolchain/llvm/lib/Support/CrashRecoveryContext.cpp:393:5
#6 0x0000f34a031648f8 (linux-vdso.so.1+0x8f8)
#7 0x0000f34a02ce2008 __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
#8 0x0000f34a02c9a83c gsignal ./signal/../sysdeps/posix/raise.c:27:6
#9 0x0000f34a02c87134 abort ./stdlib/abort.c:81:7
#10 0x0000ab544dabad08 llvm::install_out_of_memory_new_handler() /home/ubuntu/arm-toolchain/llvm/lib/Support/ErrorHandling.cpp:225:0
#11 0x0000ab544d28b134 llvm::FPPassManager::runOnFunction(llvm::Function&) /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:1408:11
#12 0x0000ab544d28f3b0 llvm::FPPassManager::runOnModule(llvm::Module&) /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:1444:16
#13 0x0000ab544d28b940 (anonymous namespace)::MPPassManager::runOnModule(llvm::Module&) /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:1513:23
#14 0x0000ab544d28b4f0 llvm::legacy::PassManagerImpl::run(llvm::Module&) /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:531:16
#15 0x0000ab544d28f6bc llvm::legacy::PassManager::run(llvm::Module&) /home/ubuntu/arm-toolchain/llvm/lib/IR/LegacyPassManager.cpp:1640:3
#16 0x0000ab544ec8c408 (anonymous namespace)::EmitAssemblyHelper::RunCodegenPipeline(clang::BackendAction, std::__1::unique_ptr>&, std::__1::unique_ptr>&) /home/ubuntu/arm-toolchain/clang/lib/CodeGen/BackendUtil.cpp:1277:19
#17 0x0000ab544ec86c54 (anonymous namespace)::EmitAssemblyHelper::emitAssembly(clang::BackendAction, std::__1::unique_ptr>, clang::BackendConsumer*) /home/ubuntu/arm-toolchain/clang/lib/CodeGen/BackendUtil.cpp:1301:3
#18 0x0000ab544ec86150 clang::emitBackendOutput(clang::CompilerInstance&, clang::CodeGenOptions&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr, std::__1::unique_ptr>, clang::BackendConsumer*) /home/ubuntu/arm-toolchain/clang/lib/CodeGen/BackendUtil.cpp:1475:13
#19 0x0000ab544ecaeffc clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) /home/ubuntu/arm-toolchain/clang/lib/CodeGen/CodeGenAction.cpp:312:3
#20 0x0000ab5451a06848 clang::ParseAST(clang::Sema&, bool, bool) /home/ubuntu/arm-toolchain/clang/lib/Parse/ParseAST.cpp:190:12
#21 0x0000ab544f5347c4 clang::ASTFrontendAction::ExecuteAction() /home/ubuntu/arm-toolchain/clang/lib/Frontend/FrontendAction.cpp:1448:1
#22 0x0000ab544ecb296c clang::CodeGenAction::ExecuteAction() /home/ubuntu/arm-
.
.
.
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 23.0.0git
Target: aarch64-unknown-none-elf
Thread model: posix
InstalledDir: /home/ubuntu/arm-toolchain/build_assertions/llvm/bin
Build config: +unoptimized, +assertions, +expensive-checks
Arm Toolchain ID: E0000-pre (f167bad1)
clang++: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/sincos-eff6a8.cpp
clang++: note: diagnostic msg: /tmp/sincos-eff6a8.sh
clang++: note: diagnostic msg:
```

[atfe_assertions.sh](https://github.com/user-attachments/files/26225033/atfe_assertions.sh)
[console_log.log](https://github.com/user-attachments/files/26225036/console_log.log)
[sincos-eff6a8.cpp](https://github.com/user-attachments/files/26225035/sincos-eff6a8.cpp)
[sincos-eff6a8.sh](https://github.com/user-attachments/files/26225034/sincos-eff6a8.sh)

Start with the failing reproducer in sincos-eff6a8.cpp and sincos-eff6a8.sh, then inspect llvm/lib/IR/LegacyPassManager.cpp around line 1404. Reproduce the assertion while building libc/src/math/generic/sincos.cpp and cos.cpp with expensive checks enabled, and use the attached logs and stack trace to narrow the CodeGen Prepare failure. Done means the build no longer aborts and the relevant regression coverage passes.

Written by the indexing model from the issue text.