forked from OSchip/llvm-project
[InstCombine] Replace one-use select operand based on condition
InstCombine already performs a fold where X == Y ? f(X) : Z is transformed to X == Y ? f(Y) : Z if f(Y) simplifies. However, if f(X) only has one use, then we can always directly replace the use inside the instruction. To actually be profitable, limit it to the case where Y is a non-expr constant. This could be further extended to replace uses further up a one-use instruction chain, but for now this only looks one level up. Among other things, this also subsumes D94860. Differential Revision: https://reviews.llvm.org/D94862
This commit is contained in:
Nikita Popov
parent
32fc32317a
commit
5238e7b302
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@ -1113,10 +1113,25 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
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// replacement cycle.
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Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
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if (TrueVal != CmpLHS &&
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isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT))
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isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT)) {
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if (Value *V = SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
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/* AllowRefinement */ true))
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return replaceOperand(Sel, Swapped ? 2 : 1, V);
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// Even if TrueVal does not simplify, we can directly replace a use of
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// CmpLHS with CmpRHS, as long as the instruction is not used anywhere
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// else. Only do this if CmpRHS is a constant, as profitability is not
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// clear for other cases.
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// FIXME: The replacement could be performed recursively.
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if (isa<Constant>(CmpRHS) && !isa<ConstantExpr>(CmpRHS))
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if (auto *I = dyn_cast<Instruction>(TrueVal))
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if (I->hasOneUse())
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for (Use &U : I->operands())
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if (U == CmpLHS) {
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replaceUse(U, CmpRHS);
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return &Sel;
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}
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}
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if (TrueVal != CmpRHS &&
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isGuaranteedNotToBeUndefOrPoison(CmpLHS, SQ.AC, &Sel, &DT))
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if (Value *V = SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, SQ,
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@ -502,7 +502,7 @@ define i32 @select_xor_icmp_bad_2(i32 %x, i32 %y, i32 %z, i32 %k) {
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define i32 @select_xor_icmp_bad_3(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_xor_icmp_bad_3(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 3
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; CHECK-NEXT: [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = xor i32 [[Z:%.*]], 3
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -541,7 +541,7 @@ define i32 @select_xor_icmp_bad_5(i32 %x, i32 %y, i32 %z) {
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define i32 @select_xor_icmp_bad_6(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_xor_icmp_bad_6(
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; CHECK-NEXT: [[A_NOT:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = xor i32 [[Z:%.*]], 1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A_NOT]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -554,7 +554,7 @@ define i32 @select_xor_icmp_bad_6(i32 %x, i32 %y, i32 %z) {
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define <2 x i8> @select_xor_icmp_vec_bad(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
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; CHECK-LABEL: @select_xor_icmp_vec_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 5, i8 3>
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; CHECK-NEXT: [[B:%.*]] = xor <2 x i8> [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = xor <2 x i8> [[Z:%.*]], <i8 5, i8 3>
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; CHECK-NEXT: [[C:%.*]] = select <2 x i1> [[A]], <2 x i8> [[B]], <2 x i8> [[Y:%.*]]
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; CHECK-NEXT: ret <2 x i8> [[C]]
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;
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@ -581,7 +581,7 @@ define <2 x i8> @select_xor_icmp_vec_undef(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z
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define i32 @select_mul_icmp_bad(i32 %x, i32 %y, i32 %z, i32 %k) {
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; CHECK-LABEL: @select_mul_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 3
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; CHECK-NEXT: [[B:%.*]] = mul i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = mul i32 [[Z:%.*]], 3
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -594,7 +594,7 @@ define i32 @select_mul_icmp_bad(i32 %x, i32 %y, i32 %z, i32 %k) {
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define i32 @select_add_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_add_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = add i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = add i32 [[Z:%.*]], 1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -619,7 +619,7 @@ define i32 @select_and_icmp_zero(i32 %x, i32 %y, i32 %z) {
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define i32 @select_or_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_or_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 3
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; CHECK-NEXT: [[B:%.*]] = or i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = or i32 [[Z:%.*]], 3
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -940,7 +940,7 @@ define float @select_fsub_fcmp_bad_2(float %x, float %y, float %z) {
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define i32 @select_sub_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_sub_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
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; CHECK-NEXT: [[B:%.*]] = sub i32 [[X]], [[Z:%.*]]
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; CHECK-NEXT: [[B:%.*]] = sub i32 0, [[Z:%.*]]
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -953,7 +953,7 @@ define i32 @select_sub_icmp_bad(i32 %x, i32 %y, i32 %z) {
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define i32 @select_sub_icmp_bad_2(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_sub_icmp_bad_2(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = sub i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = add i32 [[Z:%.*]], -1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1022,7 +1022,7 @@ define i32 @select_sub_icmp_bad_5(i32 %x, i32 %y, i32 %z, i32 %k) {
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define i32 @select_shl_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_shl_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = shl i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = shl i32 [[Z:%.*]], 1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1035,7 +1035,7 @@ define i32 @select_shl_icmp_bad(i32 %x, i32 %y, i32 %z) {
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define i32 @select_lshr_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_lshr_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = lshr i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = lshr i32 [[Z:%.*]], 1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1048,7 +1048,7 @@ define i32 @select_lshr_icmp_bad(i32 %x, i32 %y, i32 %z) {
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define i32 @select_ashr_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_ashr_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
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; CHECK-NEXT: [[B:%.*]] = ashr i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = ashr i32 [[Z:%.*]], 1
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1061,7 +1061,7 @@ define i32 @select_ashr_icmp_bad(i32 %x, i32 %y, i32 %z) {
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define i32 @select_udiv_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_udiv_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 3
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; CHECK-NEXT: [[B:%.*]] = udiv i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = udiv i32 [[Z:%.*]], 3
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1074,7 +1074,7 @@ define i32 @select_udiv_icmp_bad(i32 %x, i32 %y, i32 %z) {
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define i32 @select_sdiv_icmp_bad(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_sdiv_icmp_bad(
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; CHECK-NEXT: [[A:%.*]] = icmp eq i32 [[X:%.*]], 3
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; CHECK-NEXT: [[B:%.*]] = sdiv i32 [[Z:%.*]], [[X]]
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; CHECK-NEXT: [[B:%.*]] = sdiv i32 [[Z:%.*]], 3
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; CHECK-NEXT: [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[C]]
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;
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@ -1084,10 +1084,11 @@ define i32 @select_sdiv_icmp_bad(i32 %x, i32 %y, i32 %z) {
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ret i32 %C
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}
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; Can replace %x with 0, because sub is only used in the select.
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define i32 @select_replace_one_use(i32 %x, i32 %y) {
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; CHECK-LABEL: @select_replace_one_use(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
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; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[X]], [[Y:%.*]]
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; CHECK-NEXT: [[SUB:%.*]] = sub i32 0, [[Y:%.*]]
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; CHECK-NEXT: [[S:%.*]] = select i1 [[C]], i32 [[SUB]], i32 [[Y]]
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; CHECK-NEXT: ret i32 [[S]]
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;
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@ -1097,6 +1098,7 @@ define i32 @select_replace_one_use(i32 %x, i32 %y) {
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ret i32 %s
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}
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; Can not replace %x with 0, because %sub has other uses as well.
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define i32 @select_replace_multi_use(i32 %x, i32 %y) {
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; CHECK-LABEL: @select_replace_multi_use(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
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@ -1112,11 +1114,11 @@ define i32 @select_replace_multi_use(i32 %x, i32 %y) {
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ret i32 %s
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}
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; Case where the replacement allows the instruction to fold away.
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define i32 @select_replace_fold(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_replace_fold(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
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; CHECK-NEXT: [[FSHR:%.*]] = call i32 @llvm.fshr.i32(i32 [[Y:%.*]], i32 [[Z:%.*]], i32 [[X]])
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; CHECK-NEXT: [[S:%.*]] = select i1 [[C]], i32 [[FSHR]], i32 [[Y]]
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; CHECK-NEXT: [[S:%.*]] = select i1 [[C]], i32 [[Z:%.*]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[S]]
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;
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%c = icmp eq i32 %x, 0
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@ -1125,10 +1127,11 @@ define i32 @select_replace_fold(i32 %x, i32 %y, i32 %z) {
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ret i32 %s
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}
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; Case where %x can be replaced by 0 in multiple operands of the same instr.
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define i32 @select_replace_multiple_ops(i32 %x, i32 %y) {
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; CHECK-LABEL: @select_replace_multiple_ops(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
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; CHECK-NEXT: [[CALL:%.*]] = call i32 @dummy_call(i32 [[X]], i32 [[X]], i32 [[X]])
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; CHECK-NEXT: [[CALL:%.*]] = call i32 @dummy_call(i32 0, i32 0, i32 0)
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; CHECK-NEXT: [[S:%.*]] = select i1 [[C]], i32 [[CALL]], i32 [[Y:%.*]]
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; CHECK-NEXT: ret i32 [[S]]
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;
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@ -1138,6 +1141,8 @@ define i32 @select_replace_multiple_ops(i32 %x, i32 %y) {
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ret i32 %s
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}
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; Case where the use of %x is in a nested instruction.
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; FIXME: We only perform replacements one level up right now.
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define i32 @select_replace_nested(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_replace_nested(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
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@ -1153,6 +1158,9 @@ define i32 @select_replace_nested(i32 %x, i32 %y, i32 %z) {
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ret i32 %s
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}
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; Do not replace with constant expressions. The profitability in this case is
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; unclear, and such replacements have historically lead to infinite combine
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; loops.
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define i32 @select_replace_constexpr(i32 %x, i32 %y, i32 %z) {
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; CHECK-LABEL: @select_replace_constexpr(
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; CHECK-NEXT: [[C:%.*]] = icmp eq i32 [[X:%.*]], ptrtoint (i32* @g to i32)
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@ -1166,6 +1174,8 @@ define i32 @select_replace_constexpr(i32 %x, i32 %y, i32 %z) {
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ret i32 %s
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}
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; Don't replace with a potentially undef constant, as undef could evaluate
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; to different values for both uses.
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define <2 x i32> @select_replace_undef(<2 x i32> %x, <2 x i32> %y) {
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; CHECK-LABEL: @select_replace_undef(
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; CHECK-NEXT: [[C:%.*]] = icmp eq <2 x i32> [[X:%.*]], <i32 0, i32 undef>
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@ -17,7 +17,7 @@ define i1 @cond_eq_and(i8 %X, i8 %Y, i8 noundef %C) {
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define i1 @cond_eq_and_const(i8 %X, i8 %Y) {
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; CHECK-LABEL: @cond_eq_and_const(
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; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[X:%.*]], 10
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; CHECK-NEXT: [[LHS:%.*]] = icmp ult i8 [[X]], [[Y:%.*]]
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; CHECK-NEXT: [[LHS:%.*]] = icmp ugt i8 [[Y:%.*]], 10
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[COND]], i1 [[LHS]], i1 false
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; CHECK-NEXT: ret i1 [[RES]]
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;
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@ -43,7 +43,7 @@ define i1 @cond_eq_or(i8 %X, i8 %Y, i8 noundef %C) {
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define i1 @cond_eq_or_const(i8 %X, i8 %Y) {
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; CHECK-LABEL: @cond_eq_or_const(
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; CHECK-NEXT: [[COND:%.*]] = icmp ne i8 [[X:%.*]], 10
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; CHECK-NEXT: [[LHS:%.*]] = icmp ult i8 [[X]], [[Y:%.*]]
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; CHECK-NEXT: [[LHS:%.*]] = icmp ugt i8 [[Y:%.*]], 10
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[COND]], i1 true, i1 [[LHS]]
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; CHECK-NEXT: ret i1 [[RES]]
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;
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