The next patch in the stack needs to access CGF in these functions. 2
CGF fields are passed to these functions already; at this point it
felt natural to promote them to CGF methods.
This is a scoped helper similar to ApplyDebugLocation that creates a new source
atom group which instructions can be added to.
A source atom is a source construct that is "interesting" for debug stepping
purposes. We use an atom group number to track the instruction(s) that implement
the functionality for the atom, plus backup instructions/source locations.
---
This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.
The Key Instructions project is introduced, including a "quick summary" section
at the top which adds context for this PR, here:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668
The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.
The Clang-side work is demoed here:
https://github.com/llvm/llvm-project/pull/130943
This needs to be driver level to pass an -mllvm flag to LLVM.
Keep the flag help-hidden as the feature is under development.
---
This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.
The Key Instructions project is introduced, including a "quick summary" section
at the top which adds context for this PR, here:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668
The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.
The Clang-side work is demoed here:
https://github.com/llvm/llvm-project/pull/130943
Interpret Key Instructions metadata to determine is_stmt placement.
The lowest rank (highest precedent) instructions in each {InlinedAt, atomGroup}
set are candidates for is_stmt. Only the last instruction in each set in a given
block gets is_stmt. Calls always get is_stmt.
Given the same branch condition in `a` and `c` SimplifyCFG converts:
+> b -+
| v
--> a --> c --> e -->
| ^
+> d -+
into:
+--> bcd ---+
| v
--> a --> c --> e -->
Remap source atoms on instructions duplicated from `c` into `bcd`.
SimplifyCFG folds `b` into `a`.
+-----------+
| v
--> a --> b --> c --> d -->
| ^
+-----------------+
Remap source atoms in `b` so that the duplicated instructions are analysed
independently to determine is_stmt positions. This is necessary as the
contents of `b` may be folded into multiple preds in this way.
Add multi-pred test.
NFC for builds with LLVM_EXPERIMENTAL_KEY_INSTRUCTIONS=OFF (default).
In an ideal world we would be able to track that the merged location is used in
multiple source atoms. We can't do this though, so instead we arbitrarily but
deterministically pick one.
In cases where the InlinedAt field is unchanged we keep the atom with the
lowest non-zero rank (highest precedence). If the ranks are equal we choose
the smaller non-zero group number (arbitrary choice).
In cases where the InlinedAt field is adjusted we generate a new atom group.
Keeping the group wouldn't make sense (a source atom is identified by the
group number and InlinedAt pair) but discarding the atom info could result
in missed is_stmts.
Add unittest in MetadataTest.cpp.
Add:
mapAtomInstance - map the atom group number to a new group.
RemapSourceAtom - apply the mapped atom group number to this instruction.
Modify:
CloneBasicBlock - Call mapAtomInstance on cloned instruction's DebugLocs
if MapAtoms is true (default). Setting to false could
lead to a degraded debugging experience. See code comment.
Optimisations like loop unroll that duplicate instructions need to remap source
atom groups so that each duplicated source construct instance is considered
distinct when determining is_stmt locations.
This commit adds the remapping functionality and a unittest.
The definition EXPERIMENTAL_KEY_INSTRUCTIONS is controlled by cmake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONS.
Add IR read-write roundtrip test in a directory that is unsupported unless
the CMake flag is enabled.
In undefined mismatch cases, this was fixing the callsite to use the calling
convention of the new function. Preserve the original wrong callsite's calling
convention.
The attribute APIs make this cumbersome. There seem to be missing
overloads using AttrBuilder for the function attrs. Plus there doesn't
seem to be a direct way to set the function attrs on the call.
