[PATCH] Enhance machine CSE to capture more opportunities

[hfinkel at anl.gov]

LGTM, thanks!

================
Comment at: lib/CodeGen/MachineCSE.cpp:116
@@ -114,3 +115,3 @@
 
-bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
-                                          MachineBasicBlock *MBB) {
+/// The source register of COPY machine instruction can be propagated to all
+/// the users, and this propagation could increase the probability of finding
----------------
of COPY -> of a COPY

================
Comment at: lib/CodeGen/MachineCSE.cpp:117
@@ +116,3 @@
+/// The source register of COPY machine instruction can be propagated to all
+/// the users, and this propagation could increase the probability of finding
+/// common subexpression. If the COPY has only one user, the COPY itself can
----------------
the users -> its users

================
Comment at: lib/CodeGen/MachineCSE.cpp:118
@@ +117,3 @@
+/// the users, and this propagation could increase the probability of finding
+/// common subexpression. If the COPY has only one user, the COPY itself can
+/// be removed.
----------------
subexpression -> subexpressions

================
Comment at: lib/CodeGen/MachineCSE.cpp:158
@@ -155,2 +157,3 @@
     DEBUG(dbgs() << "***     to: " << *MI);
+    // Propagate srcreg of copies to MI.
     MO.setReg(SrcReg);
----------------
srcreg -> SrcReg

http://reviews.llvm.org/D4736