[PATCH] D94180: [SimplifyCFG] Optimize CFG when null is passed to a function with nonnull argument

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert accepted this revision.
jdoerfert added a comment.
This revision is now accepted and ready to land.

Generally LGTM, assuming you are fine with my comments. If you want to continue the discussion, we can as well.



================
Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6548
 /// Check if passing a value to an instruction will cause undefined behavior.
-static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
+static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool isUndefinedFromGEP) {
   Constant *C = dyn_cast<Constant>(V);
----------------
Nit: style `IsUndefFrom...`

I would call it differently though. I tried to understand it from the name and I couldn't. Looking at the code longer, what it basically encodes is `PtrValueMayBeModified`. So if your `C` is `null` or `undef` and not modified, it will reach the call as `null` or `undef`. If it is (potentially) modified it might reach as something other than `null`.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6572
       if (GEP->getPointerOperand() == I)
-        return passingValueIsAlwaysUndefined(V, GEP);
+        return passingValueIsAlwaysUndefined(V, GEP, true);
+
----------------
`/* IsUndef... */ true`


================
Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6599
+
+      if (C->isNullValue()) {
+        for (const llvm::Use &Arg : CB->args())
----------------



================
Comment at: llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll:209
+declare i8* @bar(i8* nonnull %p)
+declare i8* @baz(i8* noundef %p)
+
----------------
rename to `nonnull_noundef_arg`, `nonnull_arg`, etc. or something similar descriptive.


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https://reviews.llvm.org/D94180