Reimplement BranchFolding change to avoid tail merging for a 1 instruction
common tail, except when the OptimizeForSize function attribute is present.
Radar 7338114.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85441 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 66c5aa5..7bc25ab 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -18,6 +18,7 @@
#define DEBUG_TYPE "branchfolding"
#include "BranchFolding.h"
+#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
@@ -465,22 +466,23 @@
CurMPIter!=B && CurMPIter->first==CurHash;
--CurMPIter) {
for (MPIterator I = prior(CurMPIter); I->first==CurHash ; --I) {
- unsigned CommonTailLen = ComputeCommonTailLength(
- CurMPIter->second,
- I->second,
- TrialBBI1, TrialBBI2);
+ unsigned CommonTailLen = ComputeCommonTailLength(CurMPIter->second,
+ I->second,
+ TrialBBI1, TrialBBI2);
// If we will have to split a block, there should be at least
- // minCommonTailLength instructions in common; if not, at worst
- // we will be replacing a fallthrough into the common tail with a
- // branch, which at worst breaks even with falling through into
- // the duplicated common tail, so 1 instruction in common is enough.
- // We will always pick a block we do not have to split as the common
- // tail if there is one.
- // (Empty blocks will get forwarded and need not be considered.)
+ // minCommonTailLength instructions in common. Otherwise, if we are
+ // optimizing for code size, 1 instruction in common is enough. At
+ // worst we will be replacing a fallthrough into the common tail with a
+ // branch, which at worst breaks even with falling through into the
+ // duplicated common tail. We will always pick a block we do not have
+ // to split as the common tail if there is one. (Empty blocks will get
+ // forwarded and need not be considered.)
+ MachineFunction *MF = CurMPIter->second->getParent();
if (CommonTailLen >= minCommonTailLength ||
(CommonTailLen > 0 &&
- (TrialBBI1==CurMPIter->second->begin() ||
- TrialBBI2==I->second->begin()))) {
+ MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) &&
+ (TrialBBI1 == CurMPIter->second->begin() ||
+ TrialBBI2 == I->second->begin()))) {
if (CommonTailLen > maxCommonTailLength) {
SameTails.clear();
maxCommonTailLength = CommonTailLen;