diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp index c4dee6a6f00..c96741aacd2 100644 --- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp +++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp @@ -19,6 +19,31 @@ using namespace llvm; using namespace PatternMatch; + +/// simplifyValueKnownNonZero - The specific integer value is used in a context +/// where it is known to be non-zero. If this allows us to simplify the +/// computation, do so and return the new operand, otherwise return null. +static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) { + // If V has multiple uses, then we would have to do more analysis to determine + // if this is safe. For example, the use could be in dynamically unreached + // code. + if (!V->hasOneUse()) return 0; + + // ((1 << A) >>u B) --> (1 << (A-B)) + // Because V cannot be zero, we know that B is less than A. + Value *A = 0, *B = 0; ConstantInt *One = 0; + if (match(V, m_LShr(m_OneUse(m_Shl(m_ConstantInt(One), m_Value(A))), + m_Value(B))) && + // The "1" can be any value known to be a power of 2. + One->getValue().isPowerOf2()) { + A = IC.Builder->CreateSub(A, B, "tmp"); + return IC.Builder->CreateShl(One, A); + } + + return 0; +} + + /// MultiplyOverflows - True if the multiply can not be expressed in an int /// this size. static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) { @@ -293,6 +318,12 @@ bool InstCombiner::SimplifyDivRemOfSelect(BinaryOperator &I) { Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) { Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); + // The RHS is known non-zero. + if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) { + I.setOperand(1, V); + return &I; + } + // Handle cases involving: [su]div X, (select Cond, Y, Z) // This does not apply for fdiv. if (isa(Op1) && SimplifyDivRemOfSelect(I)) @@ -499,6 +530,12 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) { Instruction *InstCombiner::commonIRemTransforms(BinaryOperator &I) { Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); + // The RHS is known non-zero. + if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) { + I.setOperand(1, V); + return &I; + } + // Handle cases involving: rem X, (select Cond, Y, Z) if (isa(Op1) && SimplifyDivRemOfSelect(I)) return &I; diff --git a/test/Transforms/InstCombine/div.ll b/test/Transforms/InstCombine/div.ll index 2e24f19dce4..8a0897b972d 100644 --- a/test/Transforms/InstCombine/div.ll +++ b/test/Transforms/InstCombine/div.ll @@ -118,3 +118,17 @@ define i32 @test14(i8 %x) nounwind { ; CHECK: @test14 ; CHECK-NEXT: ret i32 0 } + +; PR9814 +define i32 @test15(i32 %a, i32 %b) nounwind { + %shl = shl i32 1, %b + %div = lshr i32 %shl, 2 + %div2 = udiv i32 %a, %div + ret i32 %div2 +; CHECK: @test15 +; CHECK-NEXT: add i32 %b, -2 +; CHECK-NEXT: lshr i32 %a, +; CHECK-NEXT: ret i32 +} + +