When deciding if it is safe to optimize a conditional branch to a CBZ or
CBNZ the offsets of the BasicBlocks from the start of the function are
estimated. For inline assembly the generic getInlineAsmLength() function is
used to get a worst case estimate of the inline assembly by multiplying the
number of instructions by the max instruction size of 4 bytes. This
unfortunately doesn't take into account the generation of Thumb implicit IT
instructions. In edge cases such as when all the instructions in the block
are 4-bytes in size and there is an implicit IT then the size is
underestimated. This can cause an out of range CBZ or CBNZ to be generated.
The patch takes a conservative approach and assumes that every instruction
in the inline assembly block may have an implicit IT.
Fixes pr31805
Differential Revision: https://reviews.llvm.org/D52834
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343960 91177308-0d34-0410-b5e6-96231b3b80d8
