[InstCombine] Increase limit for max copied from constant fold

[bcahoon]

Summary

Increasing the limits fixes several performance regressions on internal applications. The new threshold is large enough to fix the regressions.

I have not included a test case as it would be large and I'm not sure how useful it would. I can include one if needed.

[gandhi21299]

LGTM

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

 using namespace PatternMatch;
 
 #define DEBUG_TYPE "instcombine"
 
 STATISTIC(NumDeadStore, "Number of dead stores eliminated");
 STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global");
 
 static cl::opt<unsigned> MaxCopiedFromConstantUsers(
-    "instcombine-max-copied-from-constant-users", cl::init(128),
+    "instcombine-max-copied-from-constant-users", cl::init(300),
     cl::desc("Maximum users to visit in copy from constant transform"),
     cl::Hidden);
 
 /// isOnlyCopiedFromConstantMemory - Recursively walk the uses of a (derived)
 /// pointer to an alloca.  Ignore any reads of the pointer, return false if we
 /// see any stores or other unknown uses.  If we see pointer arithmetic, keep
 /// track of whether it moves the pointer (with IsOffset) but otherwise traverse
 /// the uses.  If we see a memcpy/memmove that targets an unoffseted pointer to