[PATCH] D63036: [RFC] LLVM IR constant expressions never trap.

[Eli Friedman via Phabricator via llvm-commits]

efriedma marked 2 inline comments as done.
efriedma added inline comments.


================
Comment at: lib/Analysis/ValueTracking.cpp:489
+      if (V == I || !isa<Instruction>(V) ||
+          isSafeToSpeculativelyExecute(cast<Instruction>(V))) {
        EphValues.insert(V);
----------------
jdoerfert wrote:
> `V == I` implies `isa<Instruction>(V)` and you can use `isSafeToSpeculativelyExecute(I)`
I think you're reading this backwards; isSafeToSpeculativelyExecute only executes if `V != I`


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Comment at: test/CodeGen/X86/divide-constant.ll:301
+cond.end.i:
+  %r = phi i32 [ urem (i32 ptrtoint (i32* @g1 to i32), i32 ptrtoint (i32* @g2 to i32)), %entry ], [ 1, %cond.false.i ]
+  ret i32 %r
----------------
hfinkel wrote:
> Can you check known bits? I feel like we should somehow know that `ptrtoint(@g)` isn't zero.
> 
> For a test case, we can always do `ptrtoint(@g1)/(ptrtoint(@g2)-123456)` or similar.
I don't think there's any way to prove the value is non-zero here; it's extern_weak.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D63036/new/

https://reviews.llvm.org/D63036