[llvm] r195493 - StructurizeCFG: Fix verification failure with some loops.

[Matt Arsenault]

Author: arsenm
Date: Fri Nov 22 13:24:39 2013
New Revision: 195493

URL: http://llvm.org/viewvc/llvm-project?rev=195493&view=rev
Log:
StructurizeCFG: Fix verification failure with some loops.

If the beginning of the loop was also the entry block
of the function, branches were inserted to the entry block
which isn't allowed. If this occurs, create a new dummy
function entry block that branches to the start of the loop.

Added:
    llvm/trunk/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/StructurizeCFG.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/StructurizeCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/StructurizeCFG.cpp?rev=195493&r1=195492&r2=195493&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/StructurizeCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/StructurizeCFG.cpp Fri Nov 22 13:24:39 2013
@@ -779,6 +779,20 @@ void StructurizeCFG::handleLoops(bool Ex
     handleLoops(false, LoopEnd);
   }
 
+  // If the start of the loop is the entry block, we can't branch to it so
+  // insert a new dummy entry block.
+  Function *LoopFunc = LoopStart->getParent();
+  if (LoopStart == &LoopFunc->getEntryBlock()) {
+    LoopStart->setName("entry.orig");
+
+    BasicBlock *NewEntry =
+      BasicBlock::Create(LoopStart->getContext(),
+                         "entry",
+                         LoopFunc,
+                         LoopStart);
+    BranchInst::Create(LoopStart, NewEntry);
+  }
+
   // Create an extra loop end node
   LoopEnd = needPrefix(false);
   BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);

Added: llvm/trunk/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/StructurizeCFG/no-branch-to-entry.ll?rev=195493&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/StructurizeCFG/no-branch-to-entry.ll (added)
+++ llvm/trunk/test/Transforms/StructurizeCFG/no-branch-to-entry.ll Fri Nov 22 13:24:39 2013
@@ -0,0 +1,31 @@
+; RUN: opt -S -o - -structurizecfg < %s | FileCheck %s
+
+; CHECK-LABEL: @no_branch_to_entry_undef(
+; CHECK: entry:
+; CHECK-NEXT: br label %entry.orig
+define void @no_branch_to_entry_undef(i32 addrspace(1)* %out) {
+entry:
+  br i1 undef, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  store i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+for.end:                                          ; preds = %Flow
+  ret void
+}
+
+; CHECK-LABEL: @no_branch_to_entry_true(
+; CHECK: entry:
+; CHECK-NEXT: br label %entry.orig
+define void @no_branch_to_entry_true(i32 addrspace(1)* %out) {
+entry:
+  br i1 true, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  store i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+for.end:                                          ; preds = %Flow
+  ret void
+}