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9819bcf7f1
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
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//