[llvm-bugs] [Bug 43121] New: ARM: invalid IT block in thumb2 mode

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43121

            Bug ID: 43121
           Summary: ARM: invalid IT block in thumb2 mode
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: arnd at linaro.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

While test-building random linux kernel configurations, I can across an
assembler error message:

/tmp/mISDNisar-1df18c.s: Assembler messages:
/tmp/mISDNisar-1df18c.s:8151: Error: branch must be last instruction in IT
block -- `blne _test_and_set_bit'


I reduced the test case to:

$ cat mISDNisar.c
long modeisar_ch_0_1;
int modeisar_ch_0_2, modeisar_bprotocol;
void fn1() {
  if (modeisar_ch_0_2)
    switch (modeisar_bprotocol)
    case 33:
case 34:
  if (modeisar_bprotocol == 34)
    fn2(3, &modeisar_ch_0_1);
  else
    fn2(2, &modeisar_ch_0_1);
  _Bool branch;
  int *key = 0;
  asm goto("" ::"i"(&key[branch])::l_yes);
l_yes:;
}

$ clang-9 --target=arm-linux-gnueabi -fsanitize-coverage=trace-pc
-no-integrated-as  -march=armv7-a -mthumb -c  -O2 mISDNisar.c
-Wno-implicit-function-declaration
/tmp/mISDNisar-e138de.s: Assembler messages:
/tmp/mISDNisar-e138de.s:55: Error: branch must be last instruction in IT block
-- `blne fn2'
clang: error: assembler command failed with exit code 1 (use -v to see
invocation)

$ clang-9 --version
clang version 9.0.0-svn369744-1~exp1~20190823103928.28 (branches/release_90)

Assembler output without -no-integrated-as is
$ objdump -d mISDNisar.o
00000000 <fn1>:
   0:   b5d0            push    {r4, r6, r7, lr}
   2:   af02            add     r7, sp, #8
   4:   f7ff fffe       bl      0 <__sanitizer_cov_trace_pc>
   8:   f240 0000       movw    r0, #0
   c:   f2c0 0000       movt    r0, #0
  10:   6800            ldr     r0, [r0, #0]
  12:   b1b8            cbz     r0, 44 <fn1+0x44>
  14:   f240 0000       movw    r0, #0
  18:   f2c0 0000       movt    r0, #0
  1c:   6804            ldr     r4, [r0, #0]
  1e:   f1a4 0021       sub.w   r0, r4, #33     ; 0x21
  22:   2802            cmp     r0, #2
  24:   d211            bcs.n   4a <fn1+0x4a>
  26:   f7ff fffe       bl      0 <__sanitizer_cov_trace_pc>
  2a:   f240 0100       movw    r1, #0
  2e:   2c22            cmp     r4, #34 ; 0x22
  30:   f2c0 0100       movt    r1, #0
  34:   bf1a            itte    ne
  36:   2002            movne   r0, #2
  38:   f7ff fffe       blne    0 <fn2> ; unpredictable branch in IT block
  3c:   2003            moveq   r0, #3
  3e:   f7ff fffe       bl      0 <fn2>
  42:   e005            b.n     e <__sanitizer_cov_trace_pc+0xe>
  44:   f7ff fffe       bl      0 <__sanitizer_cov_trace_pc>
  48:   e002            b.n     8 <__sanitizer_cov_trace_pc+0x8>
  4a:   f7ff fffe       bl      0 <__sanitizer_cov_trace_pc>
  4e:   e7ff            b.n     2 <__sanitizer_cov_trace_pc+0x2>
  50:   f7ff fffe       bl      0 <__sanitizer_cov_trace_pc>
  54:   bdd0            pop     {r4, r6, r7, pc}

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