[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.
llvm · May 26, 2022 · f96aa49 · f96aa49
1 parent e45087f
commit f96aa49
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Showing 2 changed files with 38 additions and 2 deletions.
diff --git 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
@@ -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
+}