[llvm] f96aa49 - [SimpleLoopUnswitch] Always skip trivial select and set condition.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-05-26T09:46:24+01:00
New Revision: f96aa493f0459d16a81e76c9d4f2915057cbcf7a

URL: https://github.com/llvm/llvm-project/commit/f96aa493f0459d16a81e76c9d4f2915057cbcf7a
DIFF: https://github.com/llvm/llvm-project/commit/f96aa493f0459d16a81e76c9d4f2915057cbcf7a.diff

LOG: [SimpleLoopUnswitch] Always skip trivial select and set condition.

When updating the branch instruction outside the loopduring non-trivial
 unswitching, always skip trivial selects and update the condition.

Otherwise we might create invalid IR, because the trivial select is
inside the loop, while the condition is outside the loop.

Fixes #55697.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
    llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-trivial-select.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index b48b628485970..198c4d76b3002 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2232,11 +2232,12 @@ static void unswitchNontrivialInvariants(
       BasicBlock *ClonedPH = ClonedPHs.begin()->second;
       BI->setSuccessor(ClonedSucc, ClonedPH);
       BI->setSuccessor(1 - ClonedSucc, LoopPH);
+      Value *Cond = skipTrivialSelect(BI->getCondition());
       if (InsertFreeze) {
-        auto Cond = skipTrivialSelect(BI->getCondition());
         if (!isGuaranteedNotToBeUndefOrPoison(Cond, &AC, BI, &DT))
-          BI->setCondition(new FreezeInst(Cond, Cond->getName() + ".fr", BI));
+          Cond = new FreezeInst(Cond, Cond->getName() + ".fr", BI);
       }
+      BI->setCondition(Cond);
       DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
     } else {
       assert(SI && "Must either be a branch or switch!");

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-trivial-select.ll b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-trivial-select.ll
index acf6802cfdaba..5280aa7d3e284 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-trivial-select.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-trivial-select.ll
@@ -82,3 +82,38 @@ loop.latch:
 exit:
   ret void
 }
+
+; Test case for PR55697.
+define i32 @unswitch_trivial_select_cmp_outside(i32 %x) {
+; CHECK-LABEL: @unswitch_trivial_select_cmp_outside(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[X:%.*]], 100
+; CHECK-NEXT:    br i1 [[C]], label [[ENTRY_SPLIT_US:%.*]], label [[ENTRY_SPLIT:%.*]]
+; CHECK:       entry.split.us:
+; CHECK-NEXT:    br label [[LOOP_US:%.*]]
+; CHECK:       loop.us:
+; CHECK-NEXT:    [[P_US:%.*]] = phi i32 [ 0, [[ENTRY_SPLIT_US]] ], [ 35, [[LOOP_US]] ]
+; CHECK-NEXT:    br label [[LOOP_US]]
+; CHECK:       entry.split:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[P:%.*]] = phi i32 [ 0, [[ENTRY_SPLIT]] ]
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 false, i1 true, i1 false
+; CHECK-NEXT:    br label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[LCSSA:%.*]] = phi i32 [ [[P]], [[LOOP]] ]
+; CHECK-NEXT:    ret i32 [[LCSSA]]
+;
+entry:
+  %c = icmp ult i32 %x, 100
+  br label %loop
+
+loop:
+  %p = phi i32 [ 0, %entry ], [ 35, %loop ]
+  %spec.select = select i1 %c, i1 true, i1 false
+  br i1 %spec.select, label %loop, label %exit
+
+exit:
+  %lcssa = phi i32 [ %p, %loop ]
+  ret i32 %lcssa
+}