[PATCH] D40639: Bail out of a SimplifyCFG switch table opt at undef values.

[Jesper Antonsson via Phabricator via llvm-commits]

JesperAntonsson created this revision.

A true or false result is expected from a comparison, but it seems the possibility of undef was overlooked, which could lead to a failed assert. This is fixed by this patch by bailing out if we encounter undef.

      

The bug is old and the assert has been there since the end of 2014, so it seems this is unusual enough to forego optimization.


https://reviews.llvm.org/D40639

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/switch_undef.ll


Index: test/Transforms/SimplifyCFG/switch_undef.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/switch_undef.ll
@@ -0,0 +1,27 @@
+; RUN: opt %s -keep-loops=false -switch-to-lookup=true -simplifycfg -S | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f6() #0 {
+; CHECK-LABEL: entry:
+; CHECK-NEXT:  br label %f1.exit.i
+; CHECK-LABEL: f1.exit.i:
+
+entry:
+  br label %for.cond.i
+
+for.cond.i:                                       ; preds = %f1.exit.i, %entry
+  switch i16 undef, label %f1.exit.i [
+    i16 -1, label %cond.false.i3.i
+    i16 1, label %cond.false.i3.i
+    i16 0, label %cond.false.i3.i
+  ]
+
+cond.false.i3.i:                                  ; preds = %for.cond.i, %for.cond.i, %for.cond.i
+  br label %f1.exit.i
+
+f1.exit.i:                                        ; preds = %cond.false.i3.i, %for.cond.i
+  %cond.i4.i = phi i16 [ undef, %cond.false.i3.i ], [ 1, %for.cond.i ]
+  %tobool7.i = icmp ne i16 %cond.i4.i, 0
+  br label %for.cond.i
+}
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5174,7 +5174,7 @@
   for (auto ValuePair : Values) {
     Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
                                                 ValuePair.second, CmpOp1, true);
-    if (!CaseConst || CaseConst == DefaultConst)
+    if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst))
       return;
     assert((CaseConst == TrueConst || CaseConst == FalseConst) &&
            "Expect true or false as compare result.");


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