Partition use lists so defs always come before uses.

This makes it possible to speed up def_iterator by stopping at the first
use. This makes def_empty() and getUniqueVRegDef() much faster when
there are many uses.

In a +Asserts build, LiveVariables is 100x faster in one case because
getVRegDef() has an assertion that would scan to the end of a
def_iterator chain.

Spill weight calculation is significantly faster (300x in one case)
because isTriviallyReMaterializable() calls MRI->isConstantPhysReg(%RIP)
which calls def_empty(%RIP).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161634 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 5 deletions

diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h
index 68905e3c5e..42a8aa43d9 100644
--- a/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -513,11 +513,20 @@ public:
       assert(Op && "Cannot increment end iterator!");
       Op = getNextOperandForReg(Op);
 
-      // If this is an operand we don't care about, skip it.
-      while (Op && ((!ReturnUses && Op->isUse()) ||
-                    (!ReturnDefs && Op->isDef()) ||
-                    (SkipDebug && Op->isDebug())))
-        Op = getNextOperandForReg(Op);
+      // All defs come before the uses, so stop def_iterator early.
+      if (!ReturnUses) {
+        if (Op) {
+          if (Op->isUse())
+            Op = 0;
+          else
+            assert(!Op->isDebug() && "Can't have debug defs");
+        }
+      } else {
+        // If this is an operand we don't care about, skip it.
+        while (Op && ((!ReturnDefs && Op->isDef()) ||
+                      (SkipDebug && Op->isDebug())))
+          Op = getNextOperandForReg(Op);
+      }
 
       return *this;
     }