Changes in directory llvm/lib/CodeGen:
BranchFolding.cpp updated: 1.35 -> 1.36
---
Log message:
Fix another case we *don't* want to do this xform.
---
Diffs of the changes: (+26 -2)
BranchFolding.cpp | 28 ++++++++++++++++++++++++++--
1 files changed, 26 insertions(+), 2 deletions(-)
Index: llvm/lib/CodeGen/BranchFolding.cpp
diff -u llvm/lib/CodeGen/BranchFolding.cpp:1.35
llvm/lib/CodeGen/BranchFolding.cpp:1.36
--- llvm/lib/CodeGen/BranchFolding.cpp:1.35 Sat Nov 18 15:30:35 2006
+++ llvm/lib/CodeGen/BranchFolding.cpp Sat Nov 18 15:56:39 2006
@@ -16,6 +16,7 @@
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "branchfolding"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineDebugInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
@@ -23,6 +24,7 @@
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
@@ -705,17 +707,39 @@
if (!PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough &&
!CanFallThrough(MBB)) {
+ bool DoTransform = true;
+
// We have to be careful that the succs of PredBB aren't both
no-successor
// blocks. If neither have successors and if PredBB is the second from
// last block in the function, we'd just keep swapping the two blocks for
// last. Only do the swap if one is clearly better to fall through than
// the other.
- if (FallThrough != --MBB->getParent()->end() ||
- IsBetterFallthrough(PriorTBB, MBB, *TII)) {
+ if (FallThrough == --MBB->getParent()->end() &&
+ !IsBetterFallthrough(PriorTBB, MBB, *TII))
+ DoTransform = false;
+
+ // We don't want to do this transformation if we have control flow like:
+ // br cond BB2
+ // BB1:
+ // ..
+ // jmp BBX
+ // BB2:
+ // ..
+ // ret
+ //
+ // In this case, we could actually be moving the return block *into* a
+ // loop!
+ if (DoTransform && !MBB->succ_empty() && !CanFallThrough(PriorTBB))
+ DoTransform = false;
+
+ if (DoTransform) {
// Reverse the branch so we will fall through on the previous true
cond.
std::vector<MachineOperand> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
+ DOUT << "\nMoving MBB: " << *MBB;
+ DOUT << "To make fallthrough to: " << *PriorTBB << "\n";
+
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond);
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