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[InstCombine] Fold abs(a * abs(b)) --> abs(a * b) (llvm#78110)
Proof: https://alive2.llvm.org/ce/z/hfbEra Fixes: llvm#73211
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‎llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

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@@ -1569,6 +1569,17 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
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if (match(IIOperand, m_Select(m_Value(), m_Neg(m_Value(X)), m_Deferred(X))))
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return replaceOperand(*II, 0, X);
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Value *Y;
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// abs(a * abs(b)) -> abs(a * b)
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if (match(IIOperand,
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m_OneUse(m_c_Mul(m_Value(X),
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m_Intrinsic<Intrinsic::abs>(m_Value(Y)))))) {
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bool NSW =
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cast<Instruction>(IIOperand)->hasNoSignedWrap() && IntMinIsPoison;
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auto *XY = NSW ? Builder.CreateNSWMul(X, Y) : Builder.CreateMul(X, Y);
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return replaceOperand(*II, 0, XY);
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}
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if (std::optional<bool> Known =
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getKnownSignOrZero(IIOperand, II, DL, &AC, &DT)) {
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// abs(x) -> x if x >= 0 (include abs(x-y) --> x - y where x >= y)

‎llvm/test/Transforms/InstCombine/abs-intrinsic.ll

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@@ -5,7 +5,136 @@ declare i8 @llvm.abs.i8(i8, i1)
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declare i32 @llvm.abs.i32(i32, i1)
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declare <4 x i32> @llvm.abs.v4i32(<4 x i32>, i1)
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declare <3 x i82> @llvm.abs.v3i82(<3 x i82>, i1)
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declare <2 x i8> @llvm.abs.v2i8(<2 x i8>, i1)
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declare void @llvm.assume(i1)
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declare void @use(i32)
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define i8 @test_abs_abs_a_mul_b_i8(i8 %a, i8 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_i8(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i8 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i8 @llvm.abs.i8(i8 [[TMP1]], i1 true)
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; CHECK-NEXT: ret i8 [[ABS2]]
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;
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%abs1 = call i8 @llvm.abs.i8(i8 %a, i1 true)
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%mul = mul i8 %abs1, %b
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%abs2 = call i8 @llvm.abs.i8(i8 %mul, i1 true)
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ret i8 %abs2
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}
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define i8 @test_abs_a_mul_abs_b_i8(i8 %a, i8 %b) {
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; CHECK-LABEL: @test_abs_a_mul_abs_b_i8(
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; CHECK-NEXT: [[A1:%.*]] = urem i8 123, [[A:%.*]]
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; CHECK-NEXT: [[TMP1:%.*]] = mul i8 [[A1]], [[B:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i8 @llvm.abs.i8(i8 [[TMP1]], i1 true)
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; CHECK-NEXT: ret i8 [[ABS2]]
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;
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%a1 = urem i8 123, %a ; thwart complexity-based canonicalization
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%abs1 = call i8 @llvm.abs.i8(i8 %b, i1 true)
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%mul = mul i8 %a1, %abs1
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%abs2 = call i8 @llvm.abs.i8(i8 %mul, i1 true)
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ret i8 %abs2
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}
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define i32 @test_abs_abs_a_mul_b_i32(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_i32(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i32 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i32 @llvm.abs.i32(i32 [[TMP1]], i1 true)
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; CHECK-NEXT: ret i32 [[ABS2]]
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;
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%abs1 = call i32 @llvm.abs.i32(i32 %a, i1 true)
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%mul = mul i32 %abs1, %b
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%abs2 = call i32 @llvm.abs.i32(i32 %mul, i1 true)
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ret i32 %abs2
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}
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define i32 @test_abs_abs_a_mul_b_i32_abs_false_true(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_i32_abs_false_true(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i32 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i32 @llvm.abs.i32(i32 [[TMP1]], i1 true)
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; CHECK-NEXT: ret i32 [[ABS2]]
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;
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%abs1 = call i32 @llvm.abs.i32(i32 %a, i1 false)
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%mul = mul i32 %abs1, %b
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%abs2 = call i32 @llvm.abs.i32(i32 %mul, i1 true)
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ret i32 %abs2
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}
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define i32 @test_abs_abs_a_mul_b_i32_abs_true_false(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_i32_abs_true_false(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i32 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i32 @llvm.abs.i32(i32 [[TMP1]], i1 false)
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; CHECK-NEXT: ret i32 [[ABS2]]
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;
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%abs1 = call i32 @llvm.abs.i32(i32 %a, i1 true)
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%mul = mul i32 %abs1, %b
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%abs2 = call i32 @llvm.abs.i32(i32 %mul, i1 false)
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ret i32 %abs2
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}
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define i32 @test_abs_abs_a_mul_b_i32_abs_false_false(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_i32_abs_false_false(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i32 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i32 @llvm.abs.i32(i32 [[TMP1]], i1 false)
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; CHECK-NEXT: ret i32 [[ABS2]]
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;
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%abs1 = call i32 @llvm.abs.i32(i32 %a, i1 false)
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%mul = mul i32 %abs1, %b
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%abs2 = call i32 @llvm.abs.i32(i32 %mul, i1 false)
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ret i32 %abs2
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}
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; this should work
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define i8 @test_nsw_with_true(i8 %a, i8 %b) {
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; CHECK-LABEL: @test_nsw_with_true(
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; CHECK-NEXT: [[TMP1:%.*]] = mul nsw i8 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i8 @llvm.abs.i8(i8 [[TMP1]], i1 true)
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; CHECK-NEXT: ret i8 [[ABS2]]
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;
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%abs1 = call i8 @llvm.abs.i8(i8 %a, i1 false)
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%mul = mul nsw i8 %abs1, %b
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%abs2 = call i8 @llvm.abs.i8(i8 %mul, i1 true)
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ret i8 %abs2
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}
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; this should't propagate the nsw
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define i8 @test_nsw_with_false(i8 %a, i8 %b) {
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; CHECK-LABEL: @test_nsw_with_false(
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; CHECK-NEXT: [[TMP1:%.*]] = mul i8 [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i8 @llvm.abs.i8(i8 [[TMP1]], i1 false)
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; CHECK-NEXT: ret i8 [[ABS2]]
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;
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%abs1 = call i8 @llvm.abs.i8(i8 %a, i1 false)
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%mul = mul nsw i8 %abs1, %b
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%abs2 = call i8 @llvm.abs.i8(i8 %mul, i1 false)
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ret i8 %abs2
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}
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define i32 @test_abs_abs_a_mul_b_more_one_use(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_more_one_use(
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; CHECK-NEXT: [[ABS1:%.*]] = call i32 @llvm.abs.i32(i32 [[A:%.*]], i1 true)
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; CHECK-NEXT: [[MUL:%.*]] = mul i32 [[ABS1]], [[B:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call i32 @llvm.abs.i32(i32 [[MUL]], i1 false)
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; CHECK-NEXT: call void @use(i32 [[MUL]])
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; CHECK-NEXT: ret i32 [[ABS2]]
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;
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%abs1 = call i32 @llvm.abs.i32(i32 %a, i1 true)
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%mul = mul i32 %abs1, %b
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%abs2 = call i32 @llvm.abs.i32(i32 %mul, i1 false)
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call void @use(i32 %mul)
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ret i32 %abs2
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}
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define <2 x i8> @test_abs_abs_a_mul_b_vector_i8(<2 x i8> %a, <2 x i8> %b) {
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; CHECK-LABEL: @test_abs_abs_a_mul_b_vector_i8(
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; CHECK-NEXT: [[TMP1:%.*]] = mul <2 x i8> [[B:%.*]], [[A:%.*]]
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; CHECK-NEXT: [[ABS2:%.*]] = call <2 x i8> @llvm.abs.v2i8(<2 x i8> [[TMP1]], i1 true)
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; CHECK-NEXT: ret <2 x i8> [[ABS2]]
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;
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%abs = call <2 x i8> @llvm.abs.v2i8(<2 x i8> %a, i1 true)
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%mul = mul <2 x i8> %abs, %b
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%abs2 = call <2 x i8> @llvm.abs.v2i8(<2 x i8> %mul, i1 true)
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ret <2 x i8> %abs2
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}
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; abs preserves trailing zeros so the second and is unneeded
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define i32 @abs_trailing_zeros(i32 %x) {

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