[SCCP] Fix crash when trying to constant-fold terminators multiple ti…

…mes.

If we fold a branch/switch to an unconditional branch to another dead block we
replace the branch with unreachable, to avoid attempting to fold the
unconditional branch.

Reviewers: davide, efriedma, mssimpso, jdoerfert

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D61300

llvm-svn: 360232

llvm/lib/Transforms/Scalar/SCCP.cpp

@@ -2083,12 +2083,22 @@ bool llvm::runIPSCCP(
         // If we have forced an edge for an indeterminate value, then force the
         // terminator to fold to that edge.
         forceIndeterminateEdge(I, Solver);
-        bool Folded = ConstantFoldTerminator(I->getParent(),
+        BasicBlock *InstBB = I->getParent();
+        bool Folded = ConstantFoldTerminator(InstBB,
                                              /*DeleteDeadConditions=*/false,
                                              /*TLI=*/nullptr, &DTU);
         assert(Folded &&
               "Expect TermInst on constantint or blockaddress to be folded");
         (void) Folded;
+        // If we folded the terminator to an unconditional branch to another
+        // dead block, replace it with Unreachable, to avoid trying to fold that
+        // branch again.
+        BranchInst *BI = cast<BranchInst>(InstBB->getTerminator());
+        if (BI && BI->isUnconditional() &&
+            !Solver.isBlockExecutable(BI->getSuccessor(0))) {
+          InstBB->getTerminator()->eraseFromParent();
+          new UnreachableInst(InstBB->getContext(), InstBB);
+        }
       }
       // Mark dead BB for deletion.
       DTU.deleteBB(DeadBB);

llvm/test/Transforms/SCCP/switch-constantfold-crash.ll

@@ -0,0 +1,92 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -ipsccp < %s -S | FileCheck %s
+; RUN: opt -passes=ipsccp < %s -S | FileCheck %s
+
+define void @barney() {
+; CHECK-LABEL: @barney(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label %bb9
+; CHECK:       bb6:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb9:
+; CHECK-NEXT:    unreachable
+;
+bb:
+  br label %bb9
+
+bb6:                                              ; preds = %bb9
+  unreachable
+
+bb7:                                              ; preds = %bb9
+  unreachable
+
+bb9:                                              ; preds = %bb
+  switch i16 0, label %bb6 [
+  i16 61, label %bb7
+  ]
+}
+
+define void @blam() {
+; CHECK-LABEL: @blam(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label %bb16
+; CHECK:       bb16:
+; CHECK-NEXT:    br label %bb38
+; CHECK:       bb38:
+; CHECK-NEXT:    unreachable
+;
+bb:
+  br label %bb16
+
+bb16:                                             ; preds = %bb
+  switch i32 0, label %bb38 [
+  i32 66, label %bb17
+  i32 63, label %bb18
+  i32 86, label %bb19
+  ]
+
+bb17:                                             ; preds = %bb16
+  unreachable
+
+bb18:                                             ; preds = %bb16
+  unreachable
+
+bb19:                                             ; preds = %bb16
+  unreachable
+
+bb38:                                             ; preds = %bb16
+  unreachable
+}
+
+
+define void @hoge() {
+; CHECK-LABEL: @hoge(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label %bb2
+; CHECK:       bb2:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb3:
+; CHECK-NEXT:    unreachable
+;
+bb:
+  switch i16 undef, label %bb1 [
+  i16 135, label %bb2
+  i16 66, label %bb2
+  ]
+
+bb1:                                              ; preds = %bb
+  ret void
+
+bb2:                                              ; preds = %bb, %bb
+  switch i16 0, label %bb3 [
+  i16 61, label %bb4
+  i16 54, label %bb4
+  i16 49, label %bb4
+  ]
+
+bb3:                                              ; preds = %bb2
+  unreachable
+
+bb4:                                              ; preds = %bb2, %bb2, %bb2
+  unreachable
+}