[ARM][LowOverheadLoops] Correct offset checking
This patch addresses a couple of problems:
1) The maximum supported offset of LE is -4094.
2) The offset of WLS also needs to be checked, this uses a
maximum positive offset of 4094.
The use of BasicBlockUtils has been changed because the block offsets
weren't being initialised, but the isBBInRange checks both positive
and negative offsets.
ARMISelLowering has been tweaked because the test case presented
another pattern that we weren't supporting.
llvm-svn: 365749
diff --git a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
index a790ab0..cedf3bd 100644
--- a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
+++ b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
@@ -91,6 +91,7 @@
MF.getSubtarget().getInstrInfo());
BBUtils = std::unique_ptr<ARMBasicBlockUtils>(new ARMBasicBlockUtils(MF));
BBUtils->computeAllBlockSizes();
+ BBUtils->adjustBBOffsetsAfter(&MF.front());
bool Changed = false;
for (auto ML : MLI) {
@@ -200,9 +201,18 @@
End->getOperand(1).getMBB() != ML->getHeader())
report_fatal_error("Expected LoopEnd to target Loop Header");
- // The LE instructions has 12-bits for the label offset.
- if (!BBUtils->isBBInRange(End, ML->getHeader(), 4096)) {
- LLVM_DEBUG(dbgs() << "ARM Loops: Too large for a low-overhead loop!\n");
+ // The WLS and LE instructions have 12-bits for the label offset. WLS
+ // requires a positive offset, while LE uses negative.
+ if (BBUtils->getOffsetOf(End) < BBUtils->getOffsetOf(ML->getHeader()) ||
+ !BBUtils->isBBInRange(End, ML->getHeader(), 4094)) {
+ LLVM_DEBUG(dbgs() << "ARM Loops: LE offset is out-of-range\n");
+ Revert = true;
+ }
+ if (Start->getOpcode() == ARM::t2WhileLoopStart &&
+ (BBUtils->getOffsetOf(Start) >
+ BBUtils->getOffsetOf(Start->getOperand(1).getMBB()) ||
+ !BBUtils->isBBInRange(Start, Start->getOperand(1).getMBB(), 4094))) {
+ LLVM_DEBUG(dbgs() << "ARM Loops: WLS offset is out-of-range!\n");
Revert = true;
}