Clarify that the bypassSlowDivision optimization operates on a single BB [v2]

Update some comments to be more explicit.

Change bypassSlowDivision and the functions it calls so that they take
BasicBlock*s and Instruction*s, rather than Function::iterator&s and
BasicBlock::iterator&s.

Change the APIs so that the caller is responsible for updating the
iterator, rather than the callee. This makes control flow much easier
to follow.

Patch by Justin Lebar!

llvm-svn: 256789

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 5844124d856..4120b454451 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -225,8 +225,14 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
   if (!OptSize && TLI && TLI->isSlowDivBypassed()) {
     const DenseMap<unsigned int, unsigned int> &BypassWidths =
        TLI->getBypassSlowDivWidths();
-    for (Function::iterator I = F.begin(); I != F.end(); I++)
-      EverMadeChange |= bypassSlowDivision(F, I, BypassWidths);
+    BasicBlock* BB = &*F.begin();
+    while (BB != nullptr) {
+      // bypassSlowDivision may create new BBs, but we don't want to reapply the
+      // optimization to those blocks.
+      BasicBlock* Next = BB->getNextNode();
+      EverMadeChange |= bypassSlowDivision(BB, BypassWidths);
+      BB = Next;
+    }
   }
 
   // Eliminate blocks that contain only PHI nodes and an