Changes in directory llvm/lib/Target/ARM:
ARMConstantIslandPass.cpp updated: 1.9 -> 1.10
---
Log message:
Conditional branch being fixed up is not the last MI in the BB, there is a
unconditional branch following it. Simply invert the condition and swap
destinations if the conditional branch can reach the destination of the
unconditional branch:
beq L1
b L2
=>
bne L2
b L1
---
Diffs of the changes: (+51 -13)
ARMConstantIslandPass.cpp | 64 ++++++++++++++++++++++++++++++++++++----------
1 files changed, 51 insertions(+), 13 deletions(-)
Index: llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
diff -u llvm/lib/Target/ARM/ARMConstantIslandPass.cpp:1.9
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp:1.10
--- llvm/lib/Target/ARM/ARMConstantIslandPass.cpp:1.9 Fri Jan 26 08:34:51 2007
+++ llvm/lib/Target/ARM/ARMConstantIslandPass.cpp Fri Jan 26 14:38:26 2007
@@ -107,6 +107,7 @@
void SplitBlockBeforeInstr(MachineInstr *MI);
void UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB);
bool HandleConstantPoolUser(MachineFunction &Fn, CPUser &U);
+ bool BBIsInBranchRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned
D);
bool FixUpImmediateBranch(MachineFunction &Fn, ImmBranch &Br);
unsigned GetInstSize(MachineInstr *MI) const;
@@ -561,6 +562,29 @@
return true;
}
+/// BBIsInBranchRange - Returns true is the distance between specific MI and
+/// specific BB can fit in MI's displacement field.
+bool ARMConstantIslands::BBIsInBranchRange(MachineInstr *MI,
+ MachineBasicBlock *DestBB,
+ unsigned MaxDisp) {
+ unsigned BrOffset = GetOffsetOf(MI);
+ unsigned DestOffset = GetOffsetOf(DestBB);
+
+ // Check to see if the destination BB is in range.
+ if (BrOffset < DestOffset) {
+ if (DestOffset - BrOffset < MaxDisp)
+ return true;
+ } else {
+ if (BrOffset - DestOffset <= MaxDisp)
+ return true;
+ }
+ return false;
+}
+
+static inline unsigned getUncondBranchDisp(int Opc) {
+ return (Opc == ARM::tB) ? (1<<10)*2 : (1<<23)*4;
+}
+
/// FixUpImmediateBranch - Fix up immediate branches whose destination is too
/// far away to fit in its displacement field. If it is a conditional branch,
/// then it is converted to an inverse conditional branch + an unconditional
@@ -571,17 +595,8 @@
MachineInstr *MI = Br.MI;
MachineBasicBlock *DestBB = MI->getOperand(0).getMachineBasicBlock();
- unsigned BrOffset = GetOffsetOf(MI);
- unsigned DestOffset = GetOffsetOf(DestBB);
-
- // Check to see if the destination BB is in range.
- if (BrOffset < DestOffset) {
- if (DestOffset - BrOffset < Br.MaxDisp)
- return false;
- } else {
- if (BrOffset - DestOffset <= Br.MaxDisp)
- return false;
- }
+ if (BBIsInBranchRange(MI, DestBB, Br.MaxDisp))
+ return false;
if (!Br.isCond) {
// Unconditional branch. We have to insert a branch somewhere to perform
@@ -604,7 +619,30 @@
// direct the updated conditional branch to the fall-through block.
Otherwise,
// split the MBB before the next instruction.
MachineBasicBlock *MBB = MI->getParent();
- if (&MBB->back() != MI || !BBHasFallthrough(MBB)) {
+ MachineInstr *BackMI = &MBB->back();
+ bool NeedSplit = (BackMI != MI) || !BBHasFallthrough(MBB);
+
+ if (BackMI != MI) {
+ if (next(MachineBasicBlock::iterator(MI)) == MBB->back() &&
+ BackMI->getOpcode() == Br.UncondBr) {
+ // Last MI in the BB is a unconditional branch. Can we simply invert the
+ // condition and swap destinations:
+ // beq L1
+ // b L2
+ // =>
+ // bne L2
+ // b L1
+ MachineBasicBlock *NewDest =
BackMI->getOperand(0).getMachineBasicBlock();
+ if (BBIsInBranchRange(MI, NewDest, Br.MaxDisp)) {
+ BackMI->getOperand(0).setMachineBasicBlock(DestBB);
+ MI->getOperand(0).setMachineBasicBlock(NewDest);
+ MI->getOperand(1).setImm(CC);
+ return true;
+ }
+ }
+ }
+
+ if (NeedSplit) {
SplitBlockBeforeInstr(MI);
// No need for the branch to the next block. We're adding a unconditional
// branch to the destination.
@@ -617,7 +655,7 @@
BuildMI(MBB, TII->get(MI->getOpcode())).addMBB(NextBB).addImm(CC);
Br.MI = &MBB->back();
BuildMI(MBB, TII->get(Br.UncondBr)).addMBB(DestBB);
- unsigned MaxDisp = (Br.UncondBr == ARM::tB) ? (1<<10)*2 : (1<<23)*4;
+ unsigned MaxDisp = getUncondBranchDisp(Br.UncondBr);
ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));
MI->eraseFromParent();
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