We assumed that A must be greater than B because the right hand side of
a remainder operator must be nonzero.
However, it is possible for A to be less than B if Pow2 is a power of
two greater than 1.
Take for example:
i32 %A = 0
i32 %B = 31
i32 Pow2 =
2147483648
((Pow2 << 0) >>u 31) is non-zero but A is less than B.
This fixes PR21274.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219713
91177308-0d34-0410-b5e6-
96231b3b80d8
// ((1 << A) >>u B) --> (1 << (A-B))
// Because V cannot be zero, we know that B is less than A.
// ((1 << A) >>u B) --> (1 << (A-B))
// Because V cannot be zero, we know that B is less than A.
- Value *A = nullptr, *B = nullptr, *PowerOf2 = nullptr;
- if (match(V, m_LShr(m_OneUse(m_Shl(m_Value(PowerOf2), m_Value(A))),
- m_Value(B))) &&
- // The "1" can be any value known to be a power of 2.
- isKnownToBeAPowerOfTwo(PowerOf2, false, 0, IC.getAssumptionTracker(),
- CxtI, IC.getDominatorTree())) {
+ Value *A = nullptr, *B = nullptr, *One = nullptr;
+ if (match(V, m_LShr(m_OneUse(m_Shl(m_Value(One), m_Value(A))), m_Value(B))) &&
+ match(One, m_One())) {
A = IC.Builder->CreateSub(A, B);
A = IC.Builder->CreateSub(A, B);
- return IC.Builder->CreateShl(PowerOf2, A);
+ return IC.Builder->CreateShl(One, A);
}
// (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
}
// (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
; CHECK-NEXT: ret i32 %a
}
; CHECK-NEXT: ret i32 %a
}
-define <2 x i32> @test31(<2 x i32> %x) nounwind {
+define <2 x i32> @test31(<2 x i32> %x) {
%shr = lshr <2 x i32> %x, <i32 31, i32 31>
%div = udiv <2 x i32> %shr, <i32 2147483647, i32 2147483647>
ret <2 x i32> %div
%shr = lshr <2 x i32> %x, <i32 31, i32 31>
%div = udiv <2 x i32> %shr, <i32 2147483647, i32 2147483647>
ret <2 x i32> %div
; CHECK-NEXT: udiv <2 x i32> %[[shr]], <i32 2147483647, i32 2147483647>
; CHECK-NEXT: ret <2 x i32>
}
; CHECK-NEXT: udiv <2 x i32> %[[shr]], <i32 2147483647, i32 2147483647>
; CHECK-NEXT: ret <2 x i32>
}
+
+define i32 @test32(i32 %a, i32 %b) {
+ %shl = shl i32 2, %b
+ %div = lshr i32 %shl, 2
+ %div2 = udiv i32 %a, %div
+ ret i32 %div2
+; CHECK-LABEL: @test32(
+; CHECK-NEXT: %[[shl:.*]] = shl i32 2, %b
+; CHECK-NEXT: %[[shr:.*]] = lshr i32 %[[shl]], 2
+; CHECK-NEXT: %[[div:.*]] = udiv i32 %a, %[[shr]]
+; CHECK-NEXT: ret i32
+}