[llvm-bugs] [Bug 31721] New: [ARM] MC crashes with LDREXD inline assembly

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31721

            Bug ID: 31721
           Summary: [ARM] MC crashes with LDREXD inline assembly
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
          Assignee: unassignedbugs at nondot.org
          Reporter: renato.golin at linaro.org
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

While investigating Bug #31058, I found that the MC layer is crashing on a
syntax previously accepted by 3.9 Clang on ARM mode:

void foo(long long *ptr, long long value) {
  int store_failed;
  __asm__ __volatile__(
      "1:\n"
      // Dummy load to lock cache line.
      "ldrexd  %1, [%2]\n"
      "teq     %0, #0\n"
      "bne     1b"
      : "=&r" (store_failed)
      : "r"(value), "r" (ptr)
      : "cc", "memory");
}

$ clang -S -O2 -target armv7a ldrexd.c -o -

llvm/include/llvm/MC/MCInst.h:75: int64_t llvm::MCOperand::getImm() const:
Assertion `isImm() && "This is not an immediate"' failed.

However, since the syntax proposed in bug #31058 works:

void foo(long long *ptr, long long value) {
  int store_failed;
  __asm__ __volatile__(
      "1:\n"
      // Dummy load to lock cache line.
      "ldrexd  %1, %H1, [%2]\n"
      "teq     %0, #0\n"
      "bne     1b"
      : "=&r" (store_failed)
      : "r"(value), "r" (ptr)
      : "cc", "memory");
}

and is preferred, we may just emit an error for this GNU syntax. Or we can fix
it and make it work on Thumb and ARM. Whatever is easier.

Also, LLVM is currently emitting an error for Thumb:

strexd.c:7:8: error: instruction requires: arm-mode
      "ldrexd  %1, [%3]\n"
strexd.c:8:8: error: instruction requires: arm-mode
      "strexd  %0, %2, [%3]\n"

which may or may not be related to bug #31720.

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