Simplify BitVector code

Instead of managing memory by hand, delegate it to std::vector. This makes the
code much simpler, and also avoids repeatedly computing the storage size.

According to valgrind --tool=callgrind, this also slightly decreases the
instruction count, but by a small margin.

This is a recommit of 82f0e3d3ea6bf927e3397b2fb423abbc5821a30f with one usage
fixed in llvm/lib/CodeGen/RegisterScavenging.cpp.

Not the slight API change: BitVector::clear() now has the same behavior as any
other container: it does not free memory, but indeed sets the size of the
BitVector to 0. It is thus incorrect to access its content right afterwards, a
scenario which wasn't enforced in previous implementation.

Differential Revision: https://reviews.llvm.org/D100387

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/RegisterScavenging.cpp b/llvm/lib/CodeGen/RegisterScavenging.cpp
index 1f23073..2ec4915 100644
--- a/llvm/lib/CodeGen/RegisterScavenging.cpp
+++ b/llvm/lib/CodeGen/RegisterScavenging.cpp
@@ -119,7 +119,7 @@ void RegScavenger::determineKillsAndDefs() {
   DefRegUnits.reset();
   for (const MachineOperand &MO : MI.operands()) {
     if (MO.isRegMask()) {
-      TmpRegUnits.clear();
+      TmpRegUnits.reset();
       for (unsigned RU = 0, RUEnd = TRI->getNumRegUnits(); RU != RUEnd; ++RU) {
         for (MCRegUnitRootIterator RURI(RU, TRI); RURI.isValid(); ++RURI) {
           if (MO.clobbersPhysReg(*RURI)) {