[InstCombine] fold more constant remainder to select-of-constants remainder

[xbolva00]

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

1431

/*FoldWithMultiUse=*/true

[spatel]

This looks like a simple extension of D122967 - cc @Chenbing.Zheng in case this was not included in the first patch for some other reason.

[Chenbing.Zheng]

In D123486#3442113, @spatel wrote:

This looks like a simple extension of D122967 - cc @Chenbing.Zheng in case this was not included in the first patch for some other reason.

Just i didn't see this todo in rem.ll. This look good to me.

[spatel]

LGTM

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

Instruction *InstCombinerImpl::commonIRemTransforms(BinaryOperator &I) {
   if (simplifyDivRemOfSelectWithZeroOp(I))
     return &I;
 
   // If the divisor is a select-of-constants, try to constant fold all rem ops:
   // C % (select Cond, TrueC, FalseC) --> select Cond, (C % TrueC), (C % FalseC)
   // TODO: Adapt simplifyDivRemOfSelectWithZeroOp to allow this and other folds.
   if (match(Op0, m_ImmConstant()) &&
       match(Op1, m_Select(m_Value(), m_ImmConstant(), m_ImmConstant()))) {
-    if (Instruction *R = FoldOpIntoSelect(I, cast<SelectInst>(Op1)))
+    if (Instruction *R = FoldOpIntoSelect(I, cast<SelectInst>(Op1), true))
       return R;
   }
 
   if (isa<Constant>(Op1)) {
     if (Instruction *Op0I = dyn_cast<Instruction>(Op0)) {
       if (SelectInst *SI = dyn_cast<SelectInst>(Op0I)) {
         if (Instruction *R = FoldOpIntoSelect(I, SI))
           return R;

llvm/test/Transforms/InstCombine/rem.ll

 ;
   %B = srem i32 %A, 2147483648 ; signbit
   %C = icmp eq i32 %B, 0 ; another equality predicate
   ret i1 %C
 }
 
 define i1 @positive_and_odd_eq(i32 %A) {
 ; CHECK-LABEL: @positive_and_odd_eq(
-; CHECK-NEXT:    [[B:%.*]] = and i32 [[A:%.*]], -2147483647
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[B]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[A:%.*]], -2147483647
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[TMP1]], 1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %B = srem i32 %A, 2
   %C = icmp eq i32 %B, 1
   ret i1 %C
 }
 
 define i1 @negative_and_odd_eq(i32 %A) {
 ; CHECK-LABEL: @negative_and_odd_eq(
 ; CHECK-NEXT:    [[B:%.*]] = srem i32 [[A:%.*]], 2
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[B]], -1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %B = srem i32 %A, 2
   %C = icmp eq i32 %B, -1
   ret i1 %C
 }
 
 define i1 @positive_and_odd_ne(i32 %A) {
 ; CHECK-LABEL: @positive_and_odd_ne(
-; CHECK-NEXT:    [[B:%.*]] = and i32 [[A:%.*]], -2147483647
-; CHECK-NEXT:    [[C:%.*]] = icmp ne i32 [[B]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[A:%.*]], -2147483647
+; CHECK-NEXT:    [[C:%.*]] = icmp ne i32 [[TMP1]], 1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %B = srem i32 %A, 2
   %C = icmp ne i32 %B, 1
   ret i1 %C
 }
 
 define i1 @negative_and_odd_ne(i32 %A) {

 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i32 6, i32 0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3
   %r = srem i32 42, %s
   ret i32 %r
 }
 
-; TODO: srem should still be replaced by select.
-
 define i32 @srem_constant_dividend_select_of_constants_divisor_use(i1 %b) {
 ; CHECK-LABEL: @srem_constant_dividend_select_of_constants_divisor_use(
 ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 12, i32 -3
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[R:%.*]] = srem i32 42, [[S]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i32 6, i32 0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3
   call void @use(i32 %s)
   %r = srem i32 42, %s
   ret i32 %r
 }
 

 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i32 6, i32 42
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3
   %r = urem i32 42, %s
   ret i32 %r
 }
 
-; TODO: urem should still be replaced by select.
-
 define i32 @urem_constant_dividend_select_of_constants_divisor_use(i1 %b) {
 ; CHECK-LABEL: @urem_constant_dividend_select_of_constants_divisor_use(
 ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 12, i32 -3
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[R:%.*]] = urem i32 42, [[S]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[B]], i32 6, i32 42
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 12, i32 -3
   call void @use(i32 %s)
   %r = urem i32 42, %s
   ret i32 %r
 }