[PATCH] D18124: ConstantFoldInstruction: avoid wasted calls to ConstantFoldConstantExpression

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The loop here calls ConstantFoldConstantExpression before knowing if all the operands are constant, which can waste a lot of time. Cuts time spent in ConstantFoldInstruction (and callees) by ~20% in our tests. Should be NFC.

Repository:
  rL LLVM

http://reviews.llvm.org/D18124

Files:
  lib/Analysis/ConstantFolding.cpp

Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -983,12 +983,14 @@
 
   // Scan the operand list, checking to see if they are all constants, if so,
   // hand off to ConstantFoldInstOperandsImpl.
+  if (!std::all_of(I->op_begin(), I->op_end(), [] (Use &U) {
+        return isa<Constant>(U);
+      }))
+    return nullptr;
+
   SmallVector<Constant*, 8> Ops;
   for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
-    Constant *Op = dyn_cast<Constant>(*i);
-    if (!Op)
-      return nullptr;  // All operands not constant!
-
+    Constant *Op = cast<Constant>(*i);
     // Fold the Instruction's operands.
     if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(Op))
       Op = ConstantFoldConstantExpression(NewCE, DL, TLI);


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