Hi,
I am trying to write a small pass. In my pass, I have inserted some
instruction and used that in another. But, during OPT it is showing
"Instruction does not dominate all uses" like following -
%b.1 = bitcast i32 4 to i32 ; <i32> [#uses=8] %11
= add i32 %a.1, %b.1 ; <i32>
[#uses=1]Instruction does not dominate all uses!
Any idea, what is wrong with this?
Regards,
Chayan
It's hard to say precisely without the whole module, but probably %b.1
doesn't dominate %11, like the error says. This is a requirement of
valid LLVM IR.
-Eli
Chayan Sarkar wrote:
Hi,
I am trying to write a small pass. In my pass, I have inserted some
instruction and used that in another. But, during OPT it is showing
"Instruction does not dominate all uses" like following -%b.1 = bitcast i32 4 to i32 ; <i32> [#uses=8] %11
= add i32 %a.1, %b.1 ; <i32>
[#uses=1]Instruction does not dominate all uses!Any idea, what is wrong with this?
Not to be snarky, but the problem is that the definition of b.1 does not dominate the use of b.1 in the add instruction.
This may be due to two reasons:
1) The instructions are in the same basic block, but they're in the wrong order. The definition of b.1 follows the use of it in the add instruction. If this is the case, you simply need to make sure your transform orders the instructions correctly within the basic block.
2) The instructions are in different basic blocks. The definition of b.1 is in a block that does not dominate the add instruction. You have either added b.1 to the wrong basic block, or you have not considered the possibility that the basic block to which b.1 belongs may not always be executed before the basic block to which the add instruction belongs.
In case you don't know what domination means in this context, a basic block A dominates a basic block B if all paths from the entry basic block of the function to basic block B pass through basic block A. Informally, if basic block B has executed, we know that basic block A has already been executed at least once, so all of the SSA definitions within it are available for use.
-- John T.
Hi,
Thank you so much for your suggestion. Actually, the use is in
different block and the use block does not dominated by the def block.
So I need to insert PHI instruction in the use block.
Regards,
Chayan