[ValueTracking] Implement sdiv/udiv support for isKnownNonNullFromDominatingCondition (#67282)

The second operand of a sdiv/udiv has to be non-null, as division by
zero is UB.

Proofs: https://alive2.llvm.org/ce/z/WttZbb

Fixes #64240.

Author: dc03

llvm/lib/Analysis/ValueTracking.cpp

@@ -2264,6 +2264,10 @@ static bool isKnownNonNullFromDominatingCondition(const Value *V,
         return true;
     }
 
+    if (match(U, m_IDiv(m_Value(), m_Specific(V))) &&
+        isValidAssumeForContext(cast<Instruction>(U), CtxI, DT))
+      return true;
+
     // Consider only compare instructions uniquely controlling a branch
     Value *RHS;
     CmpInst::Predicate Pred;

llvm/test/Analysis/ValueTracking/select-known-non-zero.ll

@@ -393,3 +393,57 @@ define i1 @inv_select_v_sle_nonneg(i8 %v, i8 %C, i8 %y) {
   %r = icmp eq i8 %s, 0
   ret i1 %r
 }
+
+; Check udiv/sdiv occuring before icmp.
+define i64 @incorrect_safe_div_1(i64 %n, i64 %d) {
+; CHECK-LABEL: @incorrect_safe_div_1(
+; CHECK-NEXT:    [[TMP1:%.*]] = udiv i64 [[N:%.*]], [[D:%.*]]
+; CHECK-NEXT:    ret i64 [[TMP1]]
+;
+  %1 = udiv i64 %n, %d
+  %2 = icmp eq i64 %d, 0
+  %3 = select i1 %2, i64 -1, i64 %1
+  ret i64 %3
+}
+
+; Check icmp occuring before udiv/sdiv.
+define i64 @incorrect_safe_div_2(i64 %n, i64 %d) {
+; CHECK-LABEL: @incorrect_safe_div_2(
+; CHECK-NEXT:    [[TMP1:%.*]] = sdiv i64 [[N:%.*]], [[D:%.*]]
+; CHECK-NEXT:    ret i64 [[TMP1]]
+;
+  %1 = icmp eq i64 %d, 0
+  %2 = sdiv i64 %n, %d
+  %3 = select i1 %1, i64 -1, i64 %2
+  ret i64 %3
+}
+
+define i64 @incorrect_safe_div_call_1(i64 %n, i64 %d) {
+; CHECK-LABEL: @incorrect_safe_div_call_1(
+; CHECK-NEXT:    [[TMP1:%.*]] = sdiv i64 [[N:%.*]], [[D:%.*]]
+; CHECK-NEXT:    tail call void @use(i64 [[D]])
+; CHECK-NEXT:    ret i64 [[TMP1]]
+;
+  %1 = sdiv i64 %n, %d
+  tail call void @use(i64 %d)
+  %2 = icmp eq i64 %d, 0
+  %3 = select i1 %2, i64 -1, i64 %1
+  ret i64 %3
+}
+
+define i64 @incorrect_safe_div_call_2(i64 %n, i64 %d) {
+; CHECK-LABEL: @incorrect_safe_div_call_2(
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[D:%.*]], 0
+; CHECK-NEXT:    tail call void @use(i64 [[D]])
+; CHECK-NEXT:    [[TMP2:%.*]] = udiv i64 [[N:%.*]], [[D]]
+; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP1]], i64 -1, i64 [[TMP2]]
+; CHECK-NEXT:    ret i64 [[TMP3]]
+;
+  %1 = icmp eq i64 %d, 0
+  tail call void @use(i64 %d)
+  %2 = udiv i64 %n, %d
+  %3 = select i1 %1, i64 -1, i64 %2
+  ret i64 %3
+}
+
+declare void @use(i64)