This patch introduces a new virtual method `TargetInstrInfo::isSafeToMove()` to allow backends to control whether a machine instruction can be safely moved by optimization passes. The `BranchFolder` pass now respects this hook when hoisting common code. By default, all instructions are considered safe to to move. For LoongArch, `isSafeToMove()` is overridden to prevent relocation-related instruction sequences (e.g. PC-relative addressing and calls) from being broken by instruction motion. Correspondingly, `isSchedulingBoundary()` is updated to reuse this logic for consistency. Relands #163725
Reverts llvm/llvm-project#163725
This patch introduces a new virtual method `TargetInstrInfo::isSafeToMove()` to allow backends to control whether a machine instruction can be safely moved by optimization passes. The `BranchFolder` pass now respects this hook when hoisting common code. By default, all instructions are considered safe to to move. For LoongArch, `isSafeToMove()` is overridden to prevent relocation-related instruction sequences (e.g. PC-relative addressing and calls) from being broken by instruction motion. Correspondingly, `isSchedulingBoundary()` is updated to reuse this logic for consistency. Fixes #163681
Depend on #152591 to fix https://github.com/llvm/llvm-project/issues/149023. Similar to an EH pad, there is no real advantage in "falling through" to an indirect target of an INLINEASM_BR. And multiple indirect targets of inline asm at the end of a function may be rotated infinitely. Therefore, this patch avoids such optimization on indirect target of inline asm as fall through.
fbf6271c7da20356d7b34583b3711b4126ca1dbb introduced an assertion failure as setDebugValueUndef was called on DBG_LABELs, which isn't allowed and doesn't make sense. Fix by skipping the call for DBG_LABELs and hoisting, in line with the original behaviour.
Reapply #140091. branch-folder hoists common instructions from TBB and FBB into their pred. Without this patch it achieves this by splicing the instructions from TBB and deleting the common ones in FBB. That moves the debug locations and debug instructions from TBB into the pred without modification, which is not ideal. Debug locations are handled in #140063. This patch handles debug instructions - in the simplest way possible, which is to just kill (undef) them. We kill and hoist the ones in FBB as well as TBB because otherwise the fact there's an assignment on the code path is deleted (which might lead to a prior location extending further than it should). There's possibly something we could do to preserve some variable locations in some cases, but this is the easiest not-incorrect thing to do. Note I had to replace the constant DBG_VALUEs to use registers in the test- it turns out setDebugValueUndef doesn't undef constant DBG_VALUEs... which feels wrong to me, but isn't something I want to touch right now. --- Fix end-iterator-dereference and add test.
Reverts llvm/llvm-project#149999 https://lab.llvm.org/buildbot/#/builders/139/builds/17622
Reapply #140091. branch-folder hoists common instructions from TBB and FBB into their pred. Without this patch it achieves this by splicing the instructions from TBB and deleting the common ones in FBB. That moves the debug locations and debug instructions from TBB into the pred without modification, which is not ideal. Debug locations are handled in #140063. This patch handles debug instructions - in the simplest way possible, which is to just kill (undef) them. We kill and hoist the ones in FBB as well as TBB because otherwise the fact there's an assignment on the code path is deleted (which might lead to a prior location extending further than it should). There's possibly something we could do to preserve some variable locations in some cases, but this is the easiest not-incorrect thing to do. Note I had to replace the constant DBG_VALUEs to use registers in the test- it turns out setDebugValueUndef doesn't undef constant DBG_VALUEs... which feels wrong to me, but isn't something I want to touch right now.
Reverts llvm/llvm-project#140091 due to crash (see comments for reproducer)
branch-folder hoists common instructions from TBB and FBB into their pred. Without this patch it achieves this by splicing the instructions from TBB and deleting the common ones in FBB. That moves the debug locations and debug instructions from TBB into the pred without modification, which is not ideal. Debug locations are handled in pull request 140063. This patch handles debug instructions - in the simplest way possible, which is to just kill (undef) them. We kill and hoist the ones in FBB as well as TBB because otherwise the fact there's an assignment on the code path is deleted (which might lead to a prior location extending further than it should). We might be able to do something smarter to preserve some variable locations in some cases, but this is the easiest not-incorrect thing to do.