Code with complex and bool crashed compiler

[tydeman]

The following code crashes clang 21.1.4 on Fedora Linux 43 on Intel x86_64

#include <assert.h>	/* assert */
#include <stddef.h>	/* offsetof */
#include <float.h>	/* FLT_SNAN */
#include <complex.h>	/* FLT_CMPLX */
#include <wchar.h>	/* wchar_t */
#include <stdio.h>	/* printf */
static       float complex  f2cx;
static      double complex  d2cx;
static long double complex ld2cx;
static struct bit2 {
      unsigned int uibf : 7;
        signed int sibf : 7;
               int pibf : 7;
              bool bobf : 1;
     unsigned char after[16];
    } bits = { 1u, 1, 1, 1 };
int main(void){
  if(1){
    struct bit2 res;
    res.bobf = bits.bobf /= CMPLXF( .125f, .125f );
    res.bobf = bits.bobf /= f2cx;
    res.bobf = bits.bobf /= CMPLX(  .125,  .125 );
    res.bobf = bits.bobf /= d2cx;
    res.bobf = bits.bobf /= CMPLXL( .125L, .125L );
    res.bobf = bits.bobf /= ld2cx;
  }
  return 0;
}

0. Program arguments: clang -g -fsanitize=memory -fsanitize=undefined -fno-sanitize=float-cast-overflow -fno-sanitize=float-divide-by-zero -H -std=c23 -m64 -mfpmath=sse -msse2 -pedantic -O0 -fno-fast-math -fdenormal-fp-math=ieee -fstrict-float-cast-overflow -fmath-errno -ftrapping-math -ffp-contract=on -fhonor-infinities -fhonor-nans -fsigned-zeros -fno-associative-math -fno-reciprocal-math -fno-unsafe-math-optimizations -fno-finite-math-only -frounding-math -ffp-model=strict -ffp-exception-behavior=strict -Xclang -disable-llvm-optzns -I/lindata/fpcets/clang64/2114/csse// -I/lindata/fpcets/common/ -I/lindata/fpcets/real/ -I/lindata/fpcets/real/bin/ -I/lindata/fpcets/real/bin/io/ -I/lindata/fpcets/cmplx/ -Wno-literal-range -Wno-unknown-pragmas -c test190.c
1. parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module 'test190.c'.
4. Running pass 'X86 DAG->DAG Instruction Selection' on function '@main'

[frederick-vs-ja]

Looks like that only UBSan triggered this bug.

Library-free reproducer (Godbolt link):

static       float _Complex  f2cx;
static      double _Complex  d2cx;
static long double _Complex ld2cx;
static struct bit2 {
      unsigned int uibf : 7;
        signed int sibf : 7;
               int pibf : 7;
              bool bobf : 1;
     unsigned char after[16];
    } bits = { 1u, 1, 1, 1 };

int main() {
  struct bit2 res;
  res.bobf = bits.bobf /= __builtin_complex( .125f, .125f );
  res.bobf = bits.bobf /= f2cx;
  res.bobf = bits.bobf /= __builtin_complex(  .125,  .125 );
  res.bobf = bits.bobf /= d2cx;
  res.bobf = bits.bobf /= __builtin_complex( .125L, .125L );
  res.bobf = bits.bobf /= ld2cx;
}

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Fred Tydeman (tydeman)

The following code crashes clang 21.1.4 on Fedora Linux 43 on Intel x86_64

#include <assert.h>	/* assert */
#include <stddef.h>	/* offsetof */
#include <float.h>	/* FLT_SNAN */
#include <complex.h>	/* FLT_CMPLX */
#include <wchar.h>	/* wchar_t */
#include <stdio.h>	/* printf */
static       float complex  f2cx;
static      double complex  d2cx;
static long double complex ld2cx;
static struct bit2 {
      unsigned int uibf : 7;
        signed int sibf : 7;
               int pibf : 7;
              bool bobf : 1;
     unsigned char after[16];
    } bits = { 1u, 1, 1, 1 };
int main(void){
  if(1){
    struct bit2 res;
    res.bobf = bits.bobf /= CMPLXF( .125f, .125f );
    res.bobf = bits.bobf /= f2cx;
    res.bobf = bits.bobf /= CMPLX(  .125,  .125 );
    res.bobf = bits.bobf /= d2cx;
    res.bobf = bits.bobf /= CMPLXL( .125L, .125L );
    res.bobf = bits.bobf /= ld2cx;
  }
  return 0;
}

0. Program arguments: clang -g -fsanitize=memory -fsanitize=undefined -fno-sanitize=float-cast-overflow -fno-sanitize=float-divide-by-zero -H -std=c23 -m64 -mfpmath=sse -msse2 -pedantic -O0 -fno-fast-math -fdenormal-fp-math=ieee -fstrict-float-cast-overflow -fmath-errno -ftrapping-math -ffp-contract=on -fhonor-infinities -fhonor-nans -fsigned-zeros -fno-associative-math -fno-reciprocal-math -fno-unsafe-math-optimizations -fno-finite-math-only -frounding-math -ffp-model=strict -ffp-exception-behavior=strict -Xclang -disable-llvm-optzns -I/lindata/fpcets/clang64/2114/csse// -I/lindata/fpcets/common/ -I/lindata/fpcets/real/ -I/lindata/fpcets/real/bin/ -I/lindata/fpcets/real/bin/io/ -I/lindata/fpcets/cmplx/ -Wno-literal-range -Wno-unknown-pragmas -c test190.c
1. <eof> parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module 'test190.c'.
4. Running pass 'X86 DAG->DAG Instruction Selection' on function '@<!-- -->main'

[arsenm]

With -emit-llvm the IR looks malformed. I see stuff like this:
%6 = icmp ule i24 %5, i8 1

[BStott6]

Been investigating this, seems like ComplexExprEmitter::EmitCompoundAssignLValue is callingEmitLoadOfScalar(LValue, SourceLocation) to load the LHS value in the case that it's a scalar, but EmitLoadOfScalar seems to assume the LValue is a simple LValue (i.e. the value can be found at getAddress), but this isn't true, as in this case it is a bitfield lvalue. I'm going to try and investigate how other code generators handle the case where an operand is a bitfield value, to see if I can put together a fix.

I think this is a bug regardless of whether UBSan is active, it's just the UBSan code path that runs into an assertion failure.