[clang] [Modules] No transitive source location change (PR #86912)

[Rainer Orth via cfe-commits]

rorth wrote:

This is certainly a case of unaligned access.  In a local build, I've run the first failing `clang` invocation under `truss` (the Solaris syscall tracer).  For
```
/var/llvm/dist-sparcv9-release-stage2-A-flang-clang18/tools/clang/stage2-bins/bin/clang -cc1 -internal-isystem /var/llvm/dist-sparcv9-release-stage2-A-flang-clang18/tools/clang/stage2-bins/lib/clang/19/include -nostdsysteminc -fmodules -Wno-private-module -fimplicit-module-maps -fmodules-cache-path=/var/llvm/dist-sparcv9-release-stage2-A-flang-clang18/tools/clang/stage2-bins/tools/clang/test/APINotes/Output/availability.m.tmp/ModulesCache -fapinotes-modules -fsyntax-only -I /vol/llvm/src/llvm-project/dist/clang/test/APINotes/Inputs/Headers -F /vol/llvm/src/llvm-project/dist/clang/test/APINotes/Inputs/Frameworks /vol/llvm/src/llvm-project/dist/clang/test/APINotes/availability.m -verify
```
this reveals
```
14552:      Incurred fault #5, FLTACCESS  %pc = 0x1083824E0
14552:        siginfo: SIGBUS BUS_ADRALN addr=0xFFFFFFFF7F5E7B6C
14552:      Received signal #10, SIGBUS [caught]
14552:        siginfo: SIGBUS BUS_ADRALN addr=0xFFFFFFFF7F5E7B6C
```
`gdb` shows exactly that:
```
Thread 2 received signal SIGBUS, Bus error.
[Switching to Thread 1 (LWP 1)]
0x00000001083824e0 in clang::ASTReader::DeclCursorForID(clang::GlobalDeclID, clang::SourceLocation&) ()
1: x/i $pc
=> 0x1083824e0 <_ZN5clang9ASTReader15DeclCursorForIDENS_12GlobalDeclIDERNS_14SourceLocationE+168>:	ldx  [ %i5 + %i1 ], %o2
(gdb) p/x $i5
$1 = 0xffffffff7f5e7b4c
(gdb) p/x $i1
$2 = 0x20
```
The `ldx` insn (Load Extended Word) takes a doubleword address with natural (64-bit) alignment.

https://github.com/llvm/llvm-project/pull/86912