[SimplifyCFG] Fix assertion failure when reusing table switch comparison

After D116332, some icmps no longer fold with the target-independent
constant folder. The SimplifyCFG code assumed that the comparison
would always fold, which is not guaranteed. Explicitly check that the
result is either true or false.

Differential Revision: https://reviews.llvm.org/D117184

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -5805,10 +5805,9 @@ static void reuseTableCompare(
   for (auto ValuePair : Values) {
     Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
                                                 ValuePair.second, CmpOp1, true);
-    if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst))
+    if (!CaseConst || CaseConst == DefaultConst ||
+        (CaseConst != TrueConst && CaseConst != FalseConst))
       return;
-    assert((CaseConst == TrueConst || CaseConst == FalseConst) &&
-           "Expect true or false as compare result.");
   }
 
   // Check if the branch instruction dominates the phi node. It's a simple

llvm/test/Transforms/SimplifyCFG/X86/switch-to-lookup-globals.ll

@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: -p
+; RUN: opt -S -passes="simplifycfg<switch-to-lookup>" < %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.ham = type <{ i32, i32, i32, i8, i8, [2 x i8] }>
+
+@global = external constant [75 x { i32, i32, i32, i8, i8 }]
+
+define i1 @zot(i32 %arg) {
+; CHECK-LABEL: @zot(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    %0 = icmp ult i32 %arg, 3
+; CHECK-NEXT:    br i1 %0, label %switch.lookup, label %bb6
+; CHECK:       switch.lookup:
+; CHECK-NEXT:    %switch.gep = getelementptr inbounds [3 x %struct.ham*], [3 x %struct.ham*]* @switch.table.zot, i32 0, i32 %arg
+; CHECK-NEXT:    %switch.load = load %struct.ham*, %struct.ham** %switch.gep, align 8
+; CHECK-NEXT:    br label %bb6
+; CHECK:       bb6:
+; CHECK-NEXT:    %tmp7 = phi %struct.ham* [ %switch.load, %switch.lookup ], [ null, %bb ]
+; CHECK-NEXT:    %tmp8 = icmp eq %struct.ham* %tmp7, bitcast (i32* getelementptr inbounds ([75 x { i32, i32, i32, i8, i8 }], [75 x { i32, i32, i32, i8, i8 }]* @global, i64 1, i64 0, i32 0) to %struct.ham*)
+; CHECK-NEXT:    ret i1 %tmp8
+;
+bb:
+  %tmp = icmp eq i32 %arg, 1
+  br i1 %tmp, label %bb6, label %bb1
+
+bb1:                                              ; preds = %bb
+  %tmp2 = icmp eq i32 %arg, 2
+  br i1 %tmp2, label %bb6, label %bb3
+
+bb3:                                              ; preds = %bb1
+  %tmp4 = icmp eq i32 %arg, 0
+  br i1 %tmp4, label %bb6, label %bb5
+
+bb5:                                              ; preds = %bb3
+  br label %bb6
+
+bb6:                                              ; preds = %bb5, %bb3, %bb1, %bb
+  %tmp7 = phi %struct.ham* [ null, %bb5 ], [ bitcast (i32* getelementptr inbounds ([75 x { i32, i32, i32, i8, i8 }], [75 x { i32, i32, i32, i8, i8 }]* @global, i64 0, i64 6, i32 0) to %struct.ham*), %bb ], [ null, %bb1 ], [ null, %bb3 ]
+  %tmp8 = icmp eq %struct.ham* %tmp7, bitcast (i32* getelementptr inbounds ([75 x { i32, i32, i32, i8, i8 }], [75 x { i32, i32, i32, i8, i8 }]* @global, i64 1, i64 0, i32 0) to %struct.ham*)
+  ret i1 %tmp8
+}