[PATCH] D38856: [IPSCCP] Remove calls without side effects

[Chris Bieneman via Phabricator via llvm-commits]

beanz added inline comments.


================
Comment at: lib/Transforms/Scalar/SCCP.cpp:1929
         if (tryToReplaceWithConstant(Solver, Inst)) {
-          if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
+          if ((!isa<CallInst>(Inst) || !Inst->mayHaveSideEffects()) &&
+              !isa<TerminatorInst>(Inst))
----------------
sanjoy wrote:
> Can we just make this `!Inst->mayHaveSideEffects() && !isa<TerminatorInst>(Inst)`?  Otherwise we're assuming that non-calls that aren't terminators are not side effecting, which may be correct specifically for the instructions that `tryToReplaceWithConstant` returns true for, but isn't true in general.
The problem with that is that we do have instructions with side effects that we want to fold away. For example we have `test/Transforms/SCCP/atomic-load-store.ll` which tests that we do erase atomic loads and stores.


https://reviews.llvm.org/D38856