From eb8eaa89a589e0a63f4053a401668d1fd916e4cd Mon Sep 17 00:00:00 2001
From: Pawel Wodnicki
SROA - We've re-written SROA to be significantly more powerful. -
+SROA - We’ve re-written SROA to be significantly more powerful and generate +code which is much more friendly to the rest of the optimization pipeline. +Previously this pass had scaling problems that required it to only operate on +relatively small aggregates, and at times it would mistakenly replace a large +aggregate with a single very large integer in order to make it a scalar SSA +value. The result was a large number of i1024 and i2048 values representing any +small stack buffer. These in turn slowed down many subsequent optimization +paths.
+The new SROA pass uses a different algorithm that allows it to only promote to +scalars the pieces of the aggregate actively in use. Because of this it doesn’t +require any thresholds. It also always deduces the scalar values from the uses +of the aggregate rather than the specific LLVM type of the aggregate. These +features combine to both optimize more code with the pass but to improve the +compile time of many functions dramatically.