Change Details

The addition of mayprogress as an LLVM IR function attribute allows us to change the way infinite side-effect free loops are eliminated. This patch modifies LoopDeletion to better optimize away dead loops. If a (possibly infinite) loop has no side effects and has the loop metadata `llvm.loop.mustprogress`, we now remove it even if we cannot compute the MaxBackedgeTaken, if the function has the `mustprogress` attribute. If the loop is not marked `llvm.loop.mustprogress` then the loop is permitted to be infinite without side-effects and we do not eliminate it. If the function is not `mustprogress` then we must prove that the loop is finite through SCEV before removing it, so the default behavior is not modified. This builds upon the changes in D85393, D86841, D86233.

The addition of maynotprogress as an LLVM IR function attribute allows us to change the way infinite side-effect free loops are eliminated. This patch modifies LoopDeletion to better optimize away dead loops. If a (possibly infinite) loop has no side effects and has the loop metadata `llvm.loop.mustprogress`, we now remove it even if we cannot compute the MaxBackedgeTaken, if the function has the `mustprogress` attribute. If the loop is not marked `llvm.loop.mustprogress` then the loop is permitted to be infinite without side-effects and we do not eliminate it. If the function does NOT have the `maynotprogress` attribute, then we must prove that the loop is finite through SCEV before removing it, so the default behavior is not modified. This builds upon the changes in D85393, D86841, D86233.

The addition of maynotprogress as an LLVM IR function attribute allows us to change the way infinite side-effect free loops are eliminated. This patch modifies LoopDeletion to better optimize away dead loops. If a (possibly infinite) loop has no side effects and has the loop metadata `llvm.loop.mustprogress`, we now remove it even if we cannot compute the MaxBackedgeTaken, if the function has the `mustprogress` attribute. If the loop is not marked `llvm.loop.mustprogress` then the loop is permitted to be infinite without side-effects and we do not eliminate it. If the function is not `musdoes NOT have the `maynotprogress` attribute, then we must prove that the loop is finite through SCEV before removing it, so the default behavior is not modified. This builds upon the changes in D85393, D86841, D86233.