comparison with 0. These two pieces of code should give identical results:
rsbs r1, r1, 0
cmp r0, r1
mov r0, #0
it ls
mov r0, #1
and:
cmn r0, r1
mov r0, #0
it ls
mov r0, #1
However, the CMN gives the *opposite* result when r1 is 0. This is because the
carry flag is set in the CMP case but not in the CMN case. In short, the CMP
instruction doesn't perform a truncate of the (logical) NOT of 0 plus the value
of r0 and the carry bit (because the "carry bit" parameter to AddWithCarry is
defined as 1 in this case, the carry flag will always be set when r0 >= 0). The
CMN instruction doesn't perform a NOT of 0 so there is never a "carry" when this
AddWithCarry is performed (because the "carry bit" parameter to AddWithCarry is
defined as 0).
The AddWithCarry in the CMP case seems to be relying upon the identity:
~x + 1 = -x
However when x is 0 and unsigned, this doesn't hold:
x = 0
~x = 0xFFFF FFFF
~x + 1 = 0x1 0000 0000
(-x = 0) != (0x1 0000 0000 = ~x + 1)
Therefore, we should disable *all* versions of CMN, especially when comparing
against zero, until we can limit when the CMN instruction is used (when we know
that the RHS is not 0) or when we have a hardware fix for this.
(See the ARM docs for the "AddWithCarry" pseudo-code.)
This is related to <rdar://problem/7569620>.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112176 91177308-0d34-0410-b5e6-96231b3b80d8
printing "lsl #0". This fixes the remaining parts of pr7792. Make
corresponding changes for encoding/decoding these instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111251 91177308-0d34-0410-b5e6-96231b3b80d8
memory and synchronization barrier dmb and dsb instructions.
- Change instruction names to something more sensible (matching name of actual
instructions).
- Added tests for memory barrier codegen.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110785 91177308-0d34-0410-b5e6-96231b3b80d8
relatively expensive comparison analyzer on each instruction. Also rename the
comparison analyzer method to something more in line with what it actually does.
This pass is will eventually be folded into the Machine CSE pass.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110539 91177308-0d34-0410-b5e6-96231b3b80d8
have 4 bits per register in the operand encoding), but have undefined
behavior when the operand value is 13 or 15 (SP and PC, respectively).
The trivial coalescer in linear scan sometimes will merge a copy from
SP into a subsequent instruction which uses the copy, and if that
instruction cannot legally reference SP, we get bad code such as:
mls r0,r9,r0,sp
instead of:
mov r2, sp
mls r0, r9, r0, r2
This patch adds a new register class for use by Thumb2 that excludes
the problematic registers (SP and PC) and is used instead of GPR
for those operands which cannot legally reference PC or SP. The
trivial coalescer explicitly requires that the register class
of the destination for the COPY instruction contain the source
register for the COPY to be considered for coalescing. This prevents
errant instructions like that above.
PR7499
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109842 91177308-0d34-0410-b5e6-96231b3b80d8
and a combine pattern to use it for setting a bit-field to a constant
value. More to come for non-constant stores.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108570 91177308-0d34-0410-b5e6-96231b3b80d8
in the literal field of an instruction. E.g.,
long long foo(long long a) {
return a - 734439407618LL;
}
rdar://7038284
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108339 91177308-0d34-0410-b5e6-96231b3b80d8
- This fixed a number of bugs in if-converter, tail merging, and post-allocation
scheduler. If-converter now runs branch folding / tail merging first to
maximize if-conversion opportunities.
- Also changed the t2IT instruction slightly. It now defines the ITSTATE
register which is read by instructions in the IT block.
- Added Thumb2 specific hazard recognizer to ensure the scheduler doesn't
change the instruction ordering in the IT block (since IT mask has been
finalized). It also ensures no other instructions can be scheduled between
instructions in the IT block.
This is not yet enabled.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106344 91177308-0d34-0410-b5e6-96231b3b80d8
I don't know of any particular reason why that would be important, but
neither can I see any reason to disallow it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104583 91177308-0d34-0410-b5e6-96231b3b80d8
Thumb2 ADD and SUB instructions: allow RSB instructions be changed to set the
condition codes, and allow RSBS instructions to be predicated.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104582 91177308-0d34-0410-b5e6-96231b3b80d8
Fix it by changing the T2I_rbin_s_is multiclass to handle the CPSR
output and 'S' suffix in the same way as T2I_bin_s_irs.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104531 91177308-0d34-0410-b5e6-96231b3b80d8
Jordy <snhjordy@gmail.com>.
Followup patches will add some tests and adjust to use Subtarget features
for the instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103119 91177308-0d34-0410-b5e6-96231b3b80d8
such that the non-VFP versions have no implicit defs of VFP registers.
If any callee-saved VFP registers are marked as having been defined, the
prologue/epilogue code will try to save and restore them.
Radar 7770432.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100892 91177308-0d34-0410-b5e6-96231b3b80d8
