When a phi node references a variable defined in a basic block dominated
by the the basic block containing the phi node, llvm-diff currently cannot determine
whether the variable is equivalent, and thus treats the phi node as different
and reports a difference. This leads to false positive differences as demonstrated
by the loop.ll diff, for which llvm-diff reports a diff when comparing the file
with itself.
Fix that issue by adding the concept of *equivalence assumptions*.
When encountering a pair of values which can neither be proven to be equivalent
nor to be non-equivalent, instead optimistically assume equivalence, and store
somewhere that the equivalence of the currently compared basic blocks depends
on this assumption.
Later, once all BBs have been processed, check all made assumptions and report
blocks as different whose equivalence was depending on an incorrect assumption,
or an assumption we could not prove to be correct.
In order to preserve the original diff report order, also schedule diffs
of blocks already known to be different using the same mechanism, so all block
diffs are now generated at the very end of function diffing.
In case an incorrect assumption was made, all further shown equivalences between
old and new values implictly depend on the incorrect assumption. Some of these
may in fact be not equivalent, but these are neither reverted nor reported,
because they are considered indirect diffs caused by an earlier direct diff.
See inline comments for an argument why we do not run into issues caused by circular
proof dependencies.
Differential Revision: https://reviews.llvm.org/D137318
Diffing phi nodes was recently added to llvm-diff.
However, there currently is a limitation where equivalent values
cannot be detected as such, leading to false positive diff reports.
If a phi node refers a value defined in a basic block dominated by
the current basic block, for example a phi node in a loop header referring
a value defined in the loop body, we cannot prove equivalence of the referred
values, because the basic block containing the variable definition has
not yet been processed.
This commit adds a test case showing this behavior, serving as a precommit
for an upcoming fix of the above.
Differential Revision: https://reviews.llvm.org/D137262
Following some recent discussions, this changes the representation
of callbrs in IR. The current blockaddress arguments are replaced
with `!` label constraints that refer directly to callbr indirect
destinations:
; Before:
%res = callbr i8* asm "", "=r,r,i"(i8* %x, i8* blockaddress(@test8, %foo))
to label %asm.fallthrough [label %foo]
; After:
%res = callbr i8* asm "", "=r,r,!i"(i8* %x)
to label %asm.fallthrough [label %foo]
The benefit of this is that we can easily update the successors of
a callbr, without having to worry about also updating blockaddress
references. This should allow us to remove some limitations:
* Allow unrolling/peeling/rotation of callbr, or any other
clone-based optimizations
(https://github.com/llvm/llvm-project/issues/41834)
* Allow duplicate successors
(https://github.com/llvm/llvm-project/issues/45248)
This is just the IR representation change though, I will follow up
with patches to remove limtations in various transformation passes
that are no longer needed.
Differential Revision: https://reviews.llvm.org/D129288
In D115311, we're looking to modify clang to emit i constraints rather
than X constraints for callbr's indirect destinations. Prior to doing
so, update all of the existing tests in llvm/ to match.
Reviewed By: void, jyknight
Differential Revision: https://reviews.llvm.org/D115410
A ConstantStruct is renamed when the LLVM context sees a new one. This
makes global variable initializers appear different when they aren't.
Instead, check the ConstantStruct for equivalence.
Differential Revision: https://reviews.llvm.org/D104734
Global initializers may be ConstantArrays. They need to be checked
explicitly, because different-yet-still-equivalent type names may be
used for each, and/or a GEP instruction may appear in one.
The only wrinkle is that we can't process the "blockaddress" arguments
of the callbr until the blocks have been equated. So we force them to be
"unified" before checking.
This was left out when the callbr instruction was added.
Differential Revision: https://reviews.llvm.org/D104606
Summary:
llvm-diff incorrectly reports that there's a diff when input IR contains undef/zeroinitializer/constantvector/indirectbr.
(This happens even if two identical files are given, e.g. `llvm-diff x.ll x.ll`)
This is fix to the bug report https://bugs.llvm.org/show_bug.cgi?id=33623 .
Reviewers: dexonsmith, rjmccall
Reviewed By: rjmccall
Subscribers: chenwj, mgrang, llvm-commits
Differential Revision: https://reviews.llvm.org/D34856
llvm-svn: 329957
