[PATCH] D18066: Add some shortcuts in Value Propagation for alloca

[David Li via llvm-commits]

davidxl added inline comments.

================
Comment at: lib/Transforms/Scalar/CorrelatedValuePropagation.cpp:322
@@ -318,1 +321,3 @@
+    // For pointer defined by AllocaInst, we know it is non-null.
     if (Type && !CS.paramHasAttr(ArgNo + 1, Attribute::NonNull) &&
+        !isa<Constant>(V) &&
----------------
Maybe add a helper function to make this more readable:

if (mayHaveNullValue(...) && ...

================
Comment at: lib/Transforms/Scalar/CorrelatedValuePropagation.cpp:324
@@ +323,3 @@
+        !isa<Constant>(V) &&
+        (dyn_cast<AllocaInst>(V) ||
+         LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
----------------
Have a helper function like:

bool isValueNonNull(V) -- which does simple checks.

So the combined check becomes:

if (mayHaveNullValue(...) && (isValueNonNull(V) || LVI ....)) {
}

Note that isValueNonNull can also handle simple cases with gep:

foo() {
   int a[10];
    ...
    bar(&a[5]);
  ...
}
we know &a[5] can not be null.



================
Comment at: test/Transforms/CorrelatedValuePropagation/alloca.ll:4
@@ +3,3 @@
+; Shortcut in Correlated Value Propagation ensures not to take Lazy Value Info
+; analysis for %a.i because %a.i is defined by alloca and we know it is not-constant.
+; CHECK-NOT: LVI Getting block end value   %a.i = alloca i64, align 8 at 'for.body'
----------------
not constant --> not null.


Repository:
  rL LLVM

http://reviews.llvm.org/D18066