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Treat the WorkSet used to find ephemeral values as double-ended
We need to make sure that we visit all operands of an instruction before moving deeper in the operand graph. We had been pushing operands onto the back of the work set, and popping them off the back as well, meaning that we might visit an instruction before visiting all of its uses that sit in between it and the call to @llvm.assume. To provide an explicit example, given the following: %q0 = extractelement <4 x float> %rd, i32 0 %q1 = extractelement <4 x float> %rd, i32 1 %q2 = extractelement <4 x float> %rd, i32 2 %q3 = extractelement <4 x float> %rd, i32 3 %q4 = fadd float %q0, %q1 %q5 = fadd float %q2, %q3 %q6 = fadd float %q4, %q5 %qi = fcmp olt float %q6, %q5 call void @llvm.assume(i1 %qi) %q5 is used by both %qi and %q6. When we visit %qi, it will be marked as ephemeral, and we'll queue %q6 and %q5. %q6 will be marked as ephemeral and we'll queue %q4 and %q5. Under the old system, we'd then visit %q4, which would become ephemeral, %q1 and then %q0, which would become ephemeral as well, and now we have a problem. We'd visit %rd, but it would not be marked as ephemeral because we've not yet visited %q2 and %q3 (because we've not yet visited %q5). This will be covered by a test case in a follow-up commit that enables ephemeral-value awareness in the SLP vectorizer. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219815 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -37,7 +37,9 @@ static void completeEphemeralValues(SmallVector<const Value *, 16> &WorkSet,
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// alive only by ephemeral values.
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while (!WorkSet.empty()) {
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const Value *V = WorkSet.pop_back_val();
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const Value *V = WorkSet.front();
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WorkSet.erase(WorkSet.begin());
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if (!Visited.insert(V))
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continue;
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