Clang's assembler doesn't ignore extraneous "#" characters in ARM inline assembly.

[llvmbot]

Bugzilla Link	20117
Version	trunk
OS	Linux
Blocks	#19300
Reporter	LLVM Bugzilla Contributor
CC	@kbeyls,@rengolin

Extended Description

I'm using Clang as packaged by Ubuntu: Ubuntu clang version 3.5-1ubuntu1 (trunk) (based on LLVM 3.5)
This doesn't seem to agree with the available options in the 'version' field.

---

Consider the following test function:

int test(void) {
int out;
asm(" ldr %0, =%1\n" : "=r" (out) : "i" (0x000f0002));
return out;
}

The instruction generated by the inline assembly is "ldr r0, =#983042", since "i" constraints get a leading hash character by default. The GNU assembler ignores this character, but Clang does not:

test.c:4:7: error: unknown token in expression
asm(" ldr %0, =%1\n" : "=r" (out) : "i" (0x000f0002));
^
:1:13: note: instantiated into assembly here
ldr r0, =#983042
^
1 error generated.

GCC has an (undocumented) substitution predicate which causes the hash character to be omitted ("ldr %0, =%c1"), and Clang appears to support this, but this still represents an incompatibility with GCC and therefore might be considered a bug.

[llvmbot]

I'm using Clang as packaged by Ubuntu: Ubuntu clang version 3.5-1ubuntu1
(trunk) (based on LLVM 3.5)
This doesn't seem to agree with the available options in the 'version' field.

Perhaps I was wrong about that, if Ubuntu have packaged a version from Clang's trunk.

[llvmbot]

I found that GAS ARM Machine Directive ".syntax unified"
responsible for successful compilation
ldr r0, =#983042

9.4.2.1 Instruction Set Syntax
...
The new, unified syntax, which can be selected via the .syntax directive,
and has the following main features:
Immediate operands do not require a # prefix.
...
So, it's really undocumented.
We have excessive #