[PATCH] D99069: [ValueTracking] Handle increasing mul recurrence in isKnownNonZero()

[JinGu Kang via Phabricator via llvm-commits]

jaykang10 added inline comments.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2459
       if (ConstantInt *C = dyn_cast<ConstantInt>(Start)) {
         if (!C->isZero() && !C->isNegative()) {
+          BinaryOperator *BO = nullptr;
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nikic wrote:
> I think the matchSimpleRecurrence() check should be higher, e.g. `PN->getNumIncomingValues() == 2` is already part of it.
Yep, you are right. I will move it up.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2461
+          BinaryOperator *BO = nullptr;
+          Value *R = nullptr, *L = nullptr;
+          if (Q.IIQ.UseInstrInfo && matchSimpleRecurrence(PN, BO, R, L)) {
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nikic wrote:
> I'd rename R/L to Start and Step.
Yep, I will rename them.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2468
+                return true;
+              if (BO->getOpcode() == Instruction::Mul && !C->isOne() &&
+                  (BO->hasNoUnsignedWrap() || BO->hasNoSignedWrap()) &&
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nikic wrote:
> Why does this exclude C = 1? `{1,*,2}<nuw>` is still non-zero. The one value is important for inequality, but here we're checking for non-zero.
You are right!!! We are checking non-zero. I will update it.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2471
+                  !StepCst->isNegative() && !StepCst->isZero() &&
+                  !StepCst->isOne())
+                return true;
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nikic wrote:
> Again, this isOne() check looks unnecessary to me.
Yep, I will update it.


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Comment at: llvm/test/Analysis/ValueTracking/monotonic-phi.ll:61
+exit:
+  %add = or i8 %A, %r
+  %cmp = icmp eq i8 %add, 0
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nikic wrote:
> Why is this or needed?
We do not need it. I will remove it.


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Comment at: llvm/test/Analysis/ValueTracking/monotonic-phi.ll:79
+  %cmp = icmp eq i8 %add, 0
+  ; CHECK-NOT: ret i1 false
+  ret i1 %cmp
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nikic wrote:
> Why does this return false? Isn't this supposed to be a negative test case, due to lack of `nuw`/`nsw`?
Yep, it is negative test case due to lack of `nuw`/`nsw`. It could be better to check `CHECK: ret i1 %cmp`. I will update it.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99069/new/

https://reviews.llvm.org/D99069