Switch lowering: fix assert in buildBitTests (PR23738)

When checking (High - Low + 1).sle(BitWidth), BitWidth would be truncated
to the size of the left-hand side. In the case of this PR, the left-hand
side was i4, so BitWidth=64 got truncated to 0 and the assert failed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239048 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7614,7 +7614,8 @@ bool SelectionDAGBuilder::buildBitTests(CaseClusterVector &Clusters,
 
   const int BitWidth =
       DAG.getTargetLoweringInfo().getPointerTy().getSizeInBits();
-  assert((High - Low + 1).sle(BitWidth) && "Case range must fit in bit mask!");
+  uint64_t Range = (High - Low).getLimitedValue(UINT64_MAX - 1) + 1;
+  assert(Range <= (uint64_t)BitWidth && "Case range must fit in bit mask!");
 
   if (Low.isNonNegative() && High.slt(BitWidth)) {
     // Optimize the case where all the case values fit in a

test/CodeGen/X86/switch.ll

@@ -534,3 +534,18 @@ return: ret void
 ; CHECK-NOT: cmpl
 ; CHECK: cmpl $99
 }
+
+
+define void @pr23738(i4 %x) {
+entry:
+  switch i4 %x, label %bb0 [
+    i4 0, label %bb1
+    i4 1, label %bb1
+    i4 -5, label %bb1
+  ]
+bb0: tail call void @g(i32 0) br label %return
+bb1: tail call void @g(i32 1) br label %return
+return: ret void
+; Don't assert due to truncating the bitwidth (64) to i4 when checking
+; that the bit-test range fits in a word.
+}