[FuncSpec] Add an option to specializing literal constant

Now the option is off by default. Since we are not sure if this option
would make the compile time increase aggressively. Although we tested it
on SPEC2017, we may need to test more to make it on by default.

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D104365

lib/Transforms/IPO/FunctionSpecialization.cpp

@@ -12,7 +12,7 @@
 //
 // Current limitations:
 // - It does not handle specialization of recursive functions,
-// - It does not yet handle integer constants, and integer ranges,
+// - It does not yet handle integer ranges.
 // - Only 1 argument per function is specialised,
 // - The cost-model could be further looked into,
 // - We are not yet caching analysis results.
@@ -64,6 +64,10 @@ static cl::opt<unsigned>
                           cl::desc("Average loop iteration count cost"),
                           cl::init(10));
 
+static cl::opt<bool> EnableSpecializationForLiteralConstant(
+    "function-specialization-for-literal-constant", cl::init(false), cl::Hidden,
+    cl::desc("Make function specialization available for literal constant."));
+
 // Helper to check if \p LV is either overdefined or a constant int.
 static bool isOverdefined(const ValueLatticeElement &LV) {
   return !LV.isUnknownOrUndef() && !LV.isConstant();
@@ -485,17 +489,11 @@ private:
         }
       }
 
-      // Get the lattice value for the value the call site passes to the
-      // argument. If this value is not constant, move on to the next call
-      // site. Additionally, set the AllConstant flag to false.
-      if (V != A && !Solver.getLatticeValueFor(V).isConstant()) {
+      if (isa<Constant>(V) && (Solver.getLatticeValueFor(V).isConstant() ||
+                               EnableSpecializationForLiteralConstant))
+        Constants.push_back(cast<Constant>(V));
+      else
         AllConstant = false;
-        continue;
-      }
-
-      // Add the constant to the set.
-      if (auto *C = dyn_cast<Constant>(CS.getArgOperand(A->getArgNo())))
-        Constants.push_back(C);
     }
 
     // If the argument can only take on constant values, AllConstant will be

test/Transforms/FunctionSpecialization/function-specialization-constant-integers.ll

@@ -0,0 +1,44 @@
+; RUN: opt -function-specialization -function-specialization-for-literal-constant=true -S < %s | FileCheck %s
+
+; Check that the literal constant parameter could be specialized.
+; CHECK: @foo.1(
+; CHECK: @foo.2(
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+declare i32 @getValue()
+declare i1 @getCond()
+
+define internal i32 @foo(i1 %break_cond) {
+entry:
+  br label %loop.entry
+
+loop.entry:
+  br label %loop2.entry
+
+loop2.entry:
+  br label %loop2.body
+
+loop2.body:
+  %value = call i32 @getValue()
+  br i1 %break_cond, label %loop2.end, label %return
+
+loop2.end:
+  %cond.end = call i1 @getCond()
+  br i1 %cond.end, label %loop2.entry, label %loop.end
+
+loop.end:
+  %cond2.end = call i1 @getCond()
+  br i1 %cond2.end, label %loop.entry, label %return
+
+return:
+  ret i32 %value
+}
+
+define dso_local i32 @bar(i32 %x, i32 %y) {
+entry:
+  %retval.1 = call i32 @foo(i1 1)
+  %retval.2 = call i32 @foo(i1 0)
+  %retval = add nsw i32 %retval.1, %retval.2
+  ret i32 %retval
+}