Fix for PR27750. Correctly handle the case where the fallthrough block and
target block are the same in getFallThroughMBB.
Differential Revision: http://reviews.llvm.org/D20288
llvm-svn: 269760
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 11c532c..acf042f 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -3927,17 +3927,21 @@
return !isPredicated(MI);
}
-// Given a MBB and its TBB, find the FBB which was a fallthrough MBB (it may not
-// be a fallthorough MBB now due to layout changes). Return nullptr if the
-// fallthough MBB cannot be identified.
+// Given a MBB and its TBB, find the FBB which was a fallthrough MBB (it may
+// not be a fallthrough MBB now due to layout changes). Return nullptr if the
+// fallthrough MBB cannot be identified.
static MachineBasicBlock *getFallThroughMBB(MachineBasicBlock *MBB,
MachineBasicBlock *TBB) {
+ // Look for non-EHPad successors other than TBB. If we find exactly one, it
+ // is the fallthrough MBB. If we find zero, then TBB is both the target MBB
+ // and fallthrough MBB. If we find more than one, we cannot identify the
+ // fallthrough MBB and should return nullptr.
MachineBasicBlock *FallthroughBB = nullptr;
for (auto SI = MBB->succ_begin(), SE = MBB->succ_end(); SI != SE; ++SI) {
- if ((*SI)->isEHPad() || *SI == TBB)
+ if ((*SI)->isEHPad() || (*SI == TBB && FallthroughBB))
continue;
// Return a nullptr if we found more than one fallthrough successor.
- if (FallthroughBB)
+ if (FallthroughBB && FallthroughBB != TBB)
return nullptr;
FallthroughBB = *SI;
}