Fix branch folding bug for indirect branches: for a block containing only

an unconditional branch (possibly from tail merging), this code is
trying to redirect all of its predecessors to go directly to the branch
target, but that isn't feasible for indirect branches.  The other
predecessors (that don't end with indirect branches) could theoretically
still be handled, but that is not easily done right now.

The AnalyzeBranch interface doesn't currently let us distinguish jump table
branches from indirect branches, and this code is currently handling
jump tables.  To avoid punting on address-taken blocks, we would have to give
up handling jump tables.  That seems like a bad tradeoff.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85975 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 455da1ad11b34afd4f609b5884e63eb5dc8dc26f..baea9642d4fdf9128ff7a5baadc35ed57a7cd6d5 100644 (file)
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -1050,7 +1050,8 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
     // If this branch is the only thing in its block, see if we can forward
     // other blocks across it.
     if (CurTBB && CurCond.empty() && CurFBB == 0 && 
-        MBB->begin()->getDesc().isBranch() && CurTBB != MBB) {
+        MBB->begin()->getDesc().isBranch() && CurTBB != MBB &&
+        !MBB->hasAddressTaken()) {
       // This block may contain just an unconditional branch.  Because there can
       // be 'non-branch terminators' in the block, try removing the branch and
       // then seeing if the block is empty.