[all-commits] [llvm/llvm-project] 35a8bd: [NFCI][IndVars] rewriteLoopExitValues(): nowadays ...

[Roman Lebedev via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 35a8bdc775817ce13a6c9b5cf81502052634aa1f
      https://github.com/llvm/llvm-project/commit/35a8bdc775817ce13a6c9b5cf81502052634aa1f
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2021-08-15 (Sun, 15 Aug 2021)

  Changed paths:
    M llvm/lib/Transforms/Utils/LoopUtils.cpp

  Log Message:
  -----------
  [NFCI][IndVars] rewriteLoopExitValues(): nowadays SCEV should not change `GEP` base pointer

Currently/previously, while SCEV guaranteed that it produces the same value,
the way it was produced may be illegal IR, so we have an ugly check that
the replacement is valid.

But now that the SCEV strictness wrt the pointer/integer types has been improved,
i believe this invariant is already upheld by the SCEV itself, natively.

I think we should add an assertion, wait for a week, and then, if all is good,
rip out all this checking.
Or we could just do the latter directly i guess.

This reverts commit rL127839.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D108043


  Commit: 77a06a9c33a6731fbe800ffaf8ca398bbe00dcba
      https://github.com/llvm/llvm-project/commit/77a06a9c33a6731fbe800ffaf8ca398bbe00dcba
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2021-08-15 (Sun, 15 Aug 2021)

  Changed paths:
    M llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll

  Log Message:
  -----------
  [NFC][SimplifyCFG] Autogenerate check lines in a test to declutter further update


  Commit: 78af5cb213b2f9fe3f47bf23947f14ac07024155
      https://github.com/llvm/llvm-project/commit/78af5cb213b2f9fe3f47bf23947f14ac07024155
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2021-08-15 (Sun, 15 Aug 2021)

  Changed paths:
    M llvm/lib/Transforms/Utils/SimplifyCFG.cpp

  Log Message:
  -----------
  [SimplifyCFG] performBranchToCommonDestFolding(): form block-closed SSA form before cloning instructions (PR51125)

LLVM IR SSA form is "implicit" in `@pr51125`. While is a valid LLVM IR,
and does not require any PHI nodes, that completely breaks the further logic
in `CloneInstructionsIntoPredecessorBlockAndUpdateSSAUses()`
that updates the live-out uses of the bonus instructions.

What i believe we need to do, is to first make the SSA form explicit,
by inserting tautological PHI nodes, and rewriting the offending uses.

```
$ /builddirs/llvm-project/build-Clang12/bin/opt -load /repositories/alive2/build-Clang-release/tv/tv.so -load-pass-plugin /repositories/alive2/build-Clang-release/tv/tv.so -tv -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -bonus-inst-threshold=10 -tv -o /dev/null /tmp/test.ll

----------------------------------------
@global_pr51125 = global 4 bytes, align 4

define i32 @pr51125() {
%entry:
  br label %L

%L:
  %ld = load i32, * @global_pr51125, align 4
  %iszero = icmp eq i32 %ld, 0
  br i1 %iszero, label %exit, label %L2

%L2:
  store i32 4294967295, * @global_pr51125, align 4
  %cmp = icmp eq i32 %ld, 4294967295
  br i1 %cmp, label %L, label %exit

%exit:
  %r = phi i32 [ %ld, %L2 ], [ %ld, %L ]
  ret i32 %r
}
=>
@global_pr51125 = global 4 bytes, align 4

define i32 @pr51125() {
%entry:
  %ld.old = load i32, * @global_pr51125, align 4
  %iszero.old = icmp eq i32 %ld.old, 0
  br i1 %iszero.old, label %exit, label %L2

%L2:
  %ld2 = phi i32 [ %ld.old, %entry ], [ %ld, %L2 ]
  store i32 4294967295, * @global_pr51125, align 4
  %cmp = icmp ne i32 %ld2, 4294967295
  %ld = load i32, * @global_pr51125, align 4
  %iszero = icmp eq i32 %ld, 0
  %or.cond = select i1 %cmp, i1 1, i1 %iszero
  br i1 %or.cond, label %exit, label %L2

%exit:
  %ld1 = phi i32 [ poison, %L2 ], [ %ld.old, %entry ]
  %r = phi i32 [ %ld2, %L2 ], [ %ld.old, %entry ]
  ret i32 %r
}
Transformation seems to be correct!

```

Fixes https://bugs.llvm.org/show_bug.cgi?id=51125

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D106317


Compare: https://github.com/llvm/llvm-project/compare/944dfa4975e8...78af5cb213b2