[PATCH] D37198: [InlineCost] add visitSelectInst()

[Chandler Carruth via Phabricator via llvm-commits]

chandlerc added inline comments.


================
Comment at: lib/Analysis/InlineCost.cpp:1201
+    // Select True, X, Y => X
+    if (CondC->isAllOnesValue() && TrueC) {
+      SimplifiedValues[&SI] = TrueC;
----------------
haicheng wrote:
> chandlerc wrote:
> > No need to separately test for true and false once you know the condition is a constant. Just check `isNullValue()`. It's either false, or true. =]
> The vector constant condition can be <i1 true, i1 false>.  It is neither AllOnesValue or NullValue.
Ah, I see.

But if you have a constant condition, even if a vector with a mixture of true and false elements, you can fully simulate the select (and we should). The test should be "is it a constant". Once we know that it is, we should be able to get at each element and test whether that element is a null value or not. And then the scalar case will just be the same as a 1-element vector.


Repository:
  rL LLVM

https://reviews.llvm.org/D37198