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InstCombine: Optimize icmp eq/ne (shl Const2, A), Const1
The following implements the optimization for sequences of the form: icmp eq/ne (shl Const2, A), Const1 Such sequences can be transformed to: icmp eq/ne A, (TrailingZeros(Const1) - TrailingZeros(Const2)) This handles only the equality operators for now. Other operators need to be handled. Patch by Ankur Garg! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220162 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -191,6 +191,8 @@ public:
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ConstantInt *DivRHS);
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Instruction *FoldICmpCstShrCst(ICmpInst &I, Value *Op, Value *A,
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ConstantInt *CI1, ConstantInt *CI2);
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Instruction *FoldICmpCstShlCst(ICmpInst &I, Value *Op, Value *A,
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ConstantInt *CI1, ConstantInt *CI2);
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Instruction *FoldICmpAddOpCst(Instruction &ICI, Value *X, ConstantInt *CI,
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ICmpInst::Predicate Pred);
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Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
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@ -1119,6 +1119,49 @@ Instruction *InstCombiner::FoldICmpCstShrCst(ICmpInst &I, Value *Op, Value *A,
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return getConstant(false);
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}
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/// FoldICmpCstShlCst - Handle "(icmp eq/ne (shl const2, A), const1)" ->
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/// (icmp eq/ne A, TrailingZeros(const1) - TrailingZeros(const2)).
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Instruction *InstCombiner::FoldICmpCstShlCst(ICmpInst &I, Value *Op, Value *A,
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ConstantInt *CI1,
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ConstantInt *CI2) {
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assert(I.isEquality() && "Cannot fold icmp gt/lt");
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auto getConstant = [&I, this](bool IsTrue) {
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if (I.getPredicate() == I.ICMP_NE)
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IsTrue = !IsTrue;
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return ReplaceInstUsesWith(I, ConstantInt::get(I.getType(), IsTrue));
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};
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auto getICmp = [&I](CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
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if (I.getPredicate() == I.ICMP_NE)
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Pred = CmpInst::getInversePredicate(Pred);
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return new ICmpInst(Pred, LHS, RHS);
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};
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APInt AP1 = CI1->getValue();
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APInt AP2 = CI2->getValue();
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assert(AP2 != 0 && "Handled in InstSimplify");
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unsigned AP2TrailingZeros = AP2.countTrailingZeros();
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if (!AP1 && AP2TrailingZeros != 0)
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return getICmp(I.ICMP_UGE, A,
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ConstantInt::get(A->getType(), AP2.getBitWidth() - AP2TrailingZeros));
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if (AP1 == AP2)
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return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
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// Get the distance between the lowest bits that are set.
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int Shift = AP1.countTrailingZeros() - AP2TrailingZeros;
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if (Shift > 0 && AP2.shl(Shift) == AP1)
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return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
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// Shifting const2 will never be equal to const1.
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return getConstant(false);
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}
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/// visitICmpInstWithInstAndIntCst - Handle "icmp (instr, intcst)".
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///
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Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
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@ -2575,13 +2618,17 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
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Builder->getInt(CI->getValue()-1));
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}
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// (icmp eq/ne (ashr/lshr const2, A), const1)
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if (I.isEquality()) {
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ConstantInt *CI2;
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if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) ||
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match(Op0, m_LShr(m_ConstantInt(CI2), m_Value(A)))) {
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// (icmp eq/ne (ashr/lshr const2, A), const1)
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return FoldICmpCstShrCst(I, Op0, A, CI, CI2);
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}
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if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
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// (icmp eq/ne (shl const2, A), const1)
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return FoldICmpCstShlCst(I, Op0, A, CI, CI2);
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}
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}
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// If this comparison is a normal comparison, it demands all
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@ -1418,3 +1418,64 @@ define i1 @icmp_and_or_lshr_cst(i32 %x) {
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%ret = icmp ne i32 %and, 0
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ret i1 %ret
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}
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; CHECK-LABEL: @shl_ap1_zero_ap2_non_zero_2
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; CHECK-NEXT: %cmp = icmp ugt i32 %a, 29
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; CHECK-NEXT: ret i1 %cmp
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define i1 @shl_ap1_zero_ap2_non_zero_2(i32 %a) {
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%shl = shl i32 4, %a
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%cmp = icmp eq i32 %shl, 0
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_zero_ap2_non_zero_4
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; CHECK-NEXT: %cmp = icmp ugt i32 %a, 30
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; CHECK-NEXT: ret i1 %cmp
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define i1 @shl_ap1_zero_ap2_non_zero_4(i32 %a) {
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%shl = shl i32 -2, %a
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%cmp = icmp eq i32 %shl, 0
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_non_zero_ap2_non_zero_both_positive
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; CHECK-NEXT: %cmp = icmp eq i32 %a, 0
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; CHECK-NEXT: ret i1 %cmp
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define i1 @shl_ap1_non_zero_ap2_non_zero_both_positive(i32 %a) {
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%shl = shl i32 50, %a
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%cmp = icmp eq i32 %shl, 50
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_non_zero_ap2_non_zero_both_negative
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; CHECK-NEXT: %cmp = icmp eq i32 %a, 0
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; CHECK-NEXT: ret i1 %cmp
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define i1 @shl_ap1_non_zero_ap2_non_zero_both_negative(i32 %a) {
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%shl = shl i32 -50, %a
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%cmp = icmp eq i32 %shl, -50
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_non_zero_ap2_non_zero_ap1_1
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; CHECK-NEXT: ret i1 false
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define i1 @shl_ap1_non_zero_ap2_non_zero_ap1_1(i32 %a) {
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%shl = shl i32 50, %a
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%cmp = icmp eq i32 %shl, 25
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_non_zero_ap2_non_zero_ap1_2
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; CHECK-NEXT: %cmp = icmp eq i32 %a, 1
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; CHECK-NEXT: ret i1 %cmp
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define i1 @shl_ap1_non_zero_ap2_non_zero_ap1_2(i32 %a) {
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%shl = shl i32 25, %a
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%cmp = icmp eq i32 %shl, 50
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ret i1 %cmp
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}
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; CHECK-LABEL: @shl_ap1_non_zero_ap2_non_zero_ap1_3
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; CHECK-NEXT: ret i1 false
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define i1 @shl_ap1_non_zero_ap2_non_zero_ap1_3(i32 %a) {
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%shl = shl i32 26, %a
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%cmp = icmp eq i32 %shl, 50
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ret i1 %cmp
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}
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