Don't match with udiv and sdiv because if the denominator is 0 we can create undef value

Author: bababuck

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -911,8 +911,6 @@ static Instruction *foldSelectZeroOrFixedOp(SelectInst &SI,
         match(FalseVal, m_c_And(m_Specific(X), m_Value(Y))) ||
         match(FalseVal, m_FShl(m_Specific(X), m_Specific(X), m_Value(Y))) ||
         match(FalseVal, m_FShr(m_Specific(X), m_Specific(X), m_Value(Y))) ||
-        match(FalseVal, m_SDiv(m_Specific(X), m_Value(Y))) ||
-        match(FalseVal, m_UDiv(m_Specific(X), m_Value(Y))) ||
         match(FalseVal,
               m_c_Intrinsic<Intrinsic::umin>(m_Specific(X), m_Value(Y))))) {
     return nullptr;

llvm/test/Transforms/InstCombine/select-fixed-zero.ll

@@ -125,9 +125,10 @@ define i64 @fshr_select_no_combine(i64 %a, i64 %b, i64 %c) {
 ; (select (icmp x, 0, eq), 0, (sdiv x, y)) -> (sdiv x, y)
 define i64 @sdiv_select(i64 %a, i64 %b) {
 ; CHECK-LABEL: @sdiv_select(
-; CHECK-NEXT:    [[B_FR:%.*]] = freeze i64 [[B:%.*]]
-; CHECK-NEXT:    [[DIV:%.*]] = sdiv i64 [[A:%.*]], [[B_FR]]
-; CHECK-NEXT:    ret i64 [[DIV]]
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[A:%.*]], 0
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv i64 [[A]], [[B_FR:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], i64 0, i64 [[DIV]]
+; CHECK-NEXT:    ret i64 [[SELECT]]
 ;
   %cond = icmp eq i64 %a, 0
   %div = sdiv i64 %a, %b
@@ -138,9 +139,10 @@ define i64 @sdiv_select(i64 %a, i64 %b) {
 ; (select (icmp x, 0, eq), 0, (udiv x, y)) -> (udiv x, y)
 define i64 @udiv_select(i64 %a, i64 %b) {
 ; CHECK-LABEL: @udiv_select(
-; CHECK-NEXT:    [[B_FR:%.*]] = freeze i64 [[B:%.*]]
-; CHECK-NEXT:    [[DIV:%.*]] = udiv i64 [[A:%.*]], [[B_FR]]
-; CHECK-NEXT:    ret i64 [[DIV]]
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[A:%.*]], 0
+; CHECK-NEXT:    [[DIV:%.*]] = udiv i64 [[A]], [[B_FR:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], i64 0, i64 [[DIV]]
+; CHECK-NEXT:    ret i64 [[SELECT]]
 ;
   %cond = icmp eq i64 %a, 0
   %div = udiv i64 %a, %b