From: Davide Italiano <davide@freebsd.org>
Date: Mon, 5 Dec 2016 23:04:21 +0000 (+0000)
Subject: [SCCP] Remove manual folding of terminator instructions.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8ea5797013603a088dd6be6ad49d1a117f1955e2;p=llvm

[SCCP] Remove manual folding of terminator instructions.

There are two cases handled here:
1) a branch on undef
2) a switch with an undef condition.

Both cases are currently handled by ResolvedUndefsIn. If we have
a branch on undef, we force its value to false (which is trivially
foldable). If we have a switch on undef, we force to the first
constant (which is also foldable).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288725 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 32f486744f5..6f4a2ae92ff 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1828,33 +1828,8 @@ static bool runIPSCCP(Module &M, const DataLayout &DL,
         // Ignore blockaddress users; BasicBlock's dtor will handle them.
         if (!I) continue;
 
-        bool Folded = ConstantFoldTerminator(I->getParent());
-        if (!Folded) {
-          // The constant folder may not have been able to fold the terminator
-          // if this is a branch or switch on undef.  Fold it manually as a
-          // branch to the first successor.
-#ifndef NDEBUG
-          if (auto *BI = dyn_cast<BranchInst>(I)) {
-            assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
-                   "Branch should be foldable!");
-          } else if (auto *SI = dyn_cast<SwitchInst>(I)) {
-            assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
-          } else {
-            llvm_unreachable("Didn't fold away reference to block!");
-          }
-#endif
-
-          // Make this an uncond branch to the first successor.
-          TerminatorInst *TI = I->getParent()->getTerminator();
-          BranchInst::Create(TI->getSuccessor(0), TI);
-
-          // Remove entries in successor phi nodes to remove edges.
-          for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
-            TI->getSuccessor(i)->removePredecessor(TI->getParent());
-
-          // Remove the old terminator.
-          TI->eraseFromParent();
-        }
+        assert(ConstantFoldTerminator(I->getParent()) &&
+          "Terminator should've been folded");
       }
 
       // Finally, delete the basic block.