[LLVMdev] ARM thumb-2 instruction used for non-thumb2 CPUs

[Damjan Marion]

Hi,

I just realized that clang produces Thumb-2 instruction in code even when older CPU type which doesn't suport Thumb-2 is specified.

Here is output:

# /opt/llvm/bin/clang -S -ccc-host-triple arm-unknown-freebsd -mcpu=arm926ej-s -mfloat-abi=soft -v -o rrx.S rrx.c
clang version 3.0 (http://llvm.org/git/clang.git 98138cdfdee05c0afbab2b209ce8cfe4a52474e1)
Target: arm-unknown-freebsd
Thread model: posix
 "/opt/llvm/bin/clang" -cc1 -triple armv5e-unknown-freebsd -S -disable-free -main-file-name rrx.c -mrelocation-model static -mdisable-fp-elim -mconstructor-aliases -target-abi apcs-gnu -target-cpu arm926ej-s -msoft-float -mfloat-abi soft -target-feature +soft-float -target-feature +soft-float-abi -target-feature -neon -target-linker-version 123.2 -momit-leaf-frame-pointer -v -coverage-file rrx.S -resource-dir /opt/llvm/bin/../lib/clang/3.0 -ferror-limit 19 -fmessage-length 162 -fno-signed-char -fgnu-runtime -fdiagnostics-show-option -fcolor-diagnostics -o rrx.S -x c rrx.c
clang -cc1 version 3.0 based upon llvm 3.0svn hosted on x86_64-apple-darwin10.7.0
#include "..." search starts here:
#include <...> search starts here:
 /opt/llvm/bin/../lib/clang/3.0/include
 /usr/include
End of search list.

Code:

void bla (long long a)
{
	if (a & ((unsigned long long)1 << 24))
        	a >>= 1;
}

generated .S:

bla:
	str	r11, [sp, #-4]!
	mov	r11, sp
	sub	sp, sp, #20
	bic	sp, sp, #7
	str	r1, [sp, #12]
	str	r0, [sp, #8]
	ldrb	r2, [sp, #11]
	tst	r2, #1
	str	r0, [sp, #4]
	str	r1, [sp]
	beq	.LBB0_2
	b	.LBB0_1
.LBB0_1:
	ldr	r0, [sp, #8]
	ldr	r1, [sp, #12]
	asrs	r1, r1, #1
	rrx	r0, r0				<< Thumb-2 instruction
	str	r1, [sp, #12]
	str	r0, [sp, #8]
.LBB0_2:
	mov	sp, r11
	ldr	r11, [sp], #4
	bx	lr






rrx r0,r0 is thumb-2 instruction, however target-cpu is set to arm926ej-s which is ARMv5E architecture and it doesn't support Thumb-2.

Is this a known issue?

Thanks,

Damjan