Optimize reserved register coalescing.
Reserved registers don't have proper live ranges, their LiveInterval
simply has a snippet of liveness for each def. Virtual registers with a
single value that is a copy of a reserved register (typically %esp) can
be coalesced with the reserved register if the live range doesn't
overlap any reserved register defs.
When coalescing with a reserved register, don't modify the reserved
register live range. Just leave it as a bunch of dead defs. This
eliminates quadratic coalescer behavior in i386 functions with many
function calls.
PR11699
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147726 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 7dd070c..bb5e65e 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -1431,6 +1431,31 @@
// than the full interfeence check below. We allow overlapping live ranges
// only when one is a copy of the other.
if (CP.isPhys()) {
+ // Optimization for reserved registers like ESP.
+ // We can only merge with a reserved physreg if RHS has a single value that
+ // is a copy of CP.DstReg(). The live range of the reserved register will
+ // look like a set of dead defs - we don't properly track the live range of
+ // reserved registers.
+ if (RegClassInfo.isReserved(CP.getDstReg())) {
+ assert(CP.isFlipped() && RHS.containsOneValue() &&
+ "Invalid join with reserved register");
+ // Deny any overlapping intervals. This depends on all the reserved
+ // register live ranges to look like dead defs.
+ for (const unsigned *AS = TRI->getOverlaps(CP.getDstReg()); *AS; ++AS) {
+ if (!LIS->hasInterval(*AS))
+ continue;
+ if (RHS.overlaps(LIS->getInterval(*AS))) {
+ DEBUG(dbgs() << "\t\tInterference: " << PrintReg(*AS, TRI) << '\n');
+ return false;
+ }
+ }
+ // Skip any value computations, we are not adding new values to the
+ // reserved register. Also skip merging the live ranges, the reserved
+ // register live range doesn't need to be accurate as long as all the
+ // defs are there.
+ return true;
+ }
+
for (const unsigned *AS = TRI->getAliasSet(CP.getDstReg()); *AS; ++AS){
if (!LIS->hasInterval(*AS))
continue;