[LLVMbugs] [Bug 18354] New: ldr= pseudo instruction produces incorrect code when using in inline assembly

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18354

            Bug ID: 18354
           Summary: ldr= pseudo instruction produces incorrect code when
                    using in 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: kristof.beyls at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Incorrect code is generated for the following function using the ldr= pseudo
instruction, when used in inline assembly


$ cat t2.c
int main() {
    int result;
    __asm volatile ("ldr %[result],=1" : [result] "=r" (result));
    return result;
}
$ clang -O3 -c -target armv7a-none-none-eabi -marm t2.c
$ llvm-objdump -disassemble t2.o

t2.o:   file format ELF32-arm

Disassembly of section .text:
main:
       0:       04 00 1f e5                                     ldr     r0,
[pc, #-4]

$d.2:
       4:       01 00 00 00                                     andeq   r0, r0,
r1

$a.3:
/work/llvm.org/cmake-git-build/bin/llvm-objdump: warning: invalid instruction
encoding
/work/llvm.org/cmake-git-build/bin/llvm-objdump: warning: invalid instruction
encoding
/work/llvm.org/cmake-git-build/bin/llvm-objdump: warning: invalid instruction
encoding
/work/llvm.org/cmake-git-build/bin/llvm-objdump: warning: invalid instruction
encoding

The constant 1 is instantiated in the middle of a code block, meaning that the
constant will be “executed”.
It seems that when I first produce an assembly file using -S, and then assemble
the resulting file, correct code is generated (i.e. the constant is outputted
after the BX LR that ends the function).

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