ARM: make branch folder remove unconditional branches

following jump tables that it earlier inserted.  This
would be OK on other targets but is needed for correctness
only on ARM (constant islands needs to find jump tables).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39782 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index 13b812ca1aea73ec3c0b219dbfbfdc9d3b9ba45c..1b936312c0a4010e48b2862ea04dbacd7be9a10f 100644 (file)
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -740,14 +740,11 @@ void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB,
             delta -= 2;
           }
         }
-        // Thumb jump tables require padding.  They can be at the end, or
-        // followed by an unconditional branch.
+        // Thumb jump tables require padding.  They should be at the end;
+        // following unconditional branches are removed by AnalyzeBranch.
         MachineInstr *ThumbJTMI = NULL;
         if (prior(MBB->end())->getOpcode() == ARM::tBR_JTr)
           ThumbJTMI = prior(MBB->end());
-        else if (prior(MBB->end()) != MBB->begin() &&
-                prior(prior(MBB->end()))->getOpcode() == ARM::tBR_JTr)
-          ThumbJTMI = prior(prior(MBB->end()));
         if (ThumbJTMI) {
           unsigned newMIOffset = GetOffsetOf(ThumbJTMI);
           unsigned oldMIOffset = newMIOffset - delta;

diff --git a/lib/Target/ARM/ARMInstrInfo.cpp b/lib/Target/ARM/ARMInstrInfo.cpp
index f4b4dbe2e3a69cd6894ea7817fc8713d198f5fd9..b404ec078e51e9d3e2c40593a9fe1bc0a35b4e8e 100644 (file)
--- a/lib/Target/ARM/ARMInstrInfo.cpp
+++ b/lib/Target/ARM/ARMInstrInfo.cpp
@@ -350,8 +350,8 @@ bool ARMInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,MachineBasicBlock *&TBB,
     return false;
   }
   
-  // If the block ends with two B's or tB's, handle it.  The second one is not
-  // executed, so remove it.
+  // If the block ends with two unconditional branches, handle it.  The second 
+  // one is not executed, so remove it.
   if ((SecondLastOpc == ARM::B || SecondLastOpc==ARM::tB) &&
       (LastOpc == ARM::B || LastOpc == ARM::tB)) {
     TBB = SecondLastInst->getOperand(0).getMachineBasicBlock();
@@ -360,6 +360,17 @@ bool ARMInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,MachineBasicBlock *&TBB,
     return false;
   }
 
+  // Likewise if it ends with a branch table followed by an unconditional branch.
+  // The branch folder can create these, and we must get rid of them for
+  // correctness of Thumb constant islands.
+  if ((SecondLastOpc == ARM::BR_JTr || SecondLastOpc==ARM::BR_JTm ||
+       SecondLastOpc == ARM::BR_JTadd || SecondLastOpc==ARM::tBR_JTr) &&
+      (LastOpc == ARM::B || LastOpc == ARM::tB)) {
+    I = LastInst;
+    I->eraseFromParent();
+    return true;
+  } 
+
   // Otherwise, can't handle this.
   return true;
 }