NFC: Migrate SpeculativeExecution to work on InstructionCost

This patch migrates cost values and arithmetic to work on InstructionCost.
When the interfaces to TargetTransformInfo are changed, any InstructionCost
state will propagate naturally.

See this patch for the introduction of the type: https://reviews.llvm.org/D91174
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2020-November/146408.html

Reviewed By: david-arm

Differential Revision: https://reviews.llvm.org/D95356

Author: sdesmalen-arm

llvm/lib/Transforms/Scalar/SpeculativeExecution.cpp

@@ -210,8 +210,8 @@ bool SpeculativeExecutionPass::runOnBasicBlock(BasicBlock &B) {
   return false;
 }
 
-static unsigned ComputeSpeculationCost(const Instruction *I,
-                                       const TargetTransformInfo &TTI) {
+static InstructionCost ComputeSpeculationCost(const Instruction *I,
+                                              const TargetTransformInfo &TTI) {
   switch (Operator::getOpcode(I)) {
     case Instruction::GetElementPtr:
     case Instruction::Add:
@@ -255,7 +255,8 @@ static unsigned ComputeSpeculationCost(const Instruction *I,
       return TTI.getUserCost(I, TargetTransformInfo::TCK_SizeAndLatency);
 
     default:
-      return UINT_MAX; // Disallow anything not explicitly listed.
+      return InstructionCost::getInvalid(); // Disallow anything not explicitly
+                                            // listed.
   }
 }
 
@@ -288,11 +289,11 @@ bool SpeculativeExecutionPass::considerHoistingFromTo(
     return true;
   };
 
-  unsigned TotalSpeculationCost = 0;
+  InstructionCost TotalSpeculationCost = 0;
   unsigned NotHoistedInstCount = 0;
   for (const auto &I : FromBlock) {
-    const unsigned Cost = ComputeSpeculationCost(&I, *TTI);
-    if (Cost != UINT_MAX && isSafeToSpeculativelyExecute(&I) &&
+    const InstructionCost Cost = ComputeSpeculationCost(&I, *TTI);
+    if (Cost.isValid() && isSafeToSpeculativelyExecute(&I) &&
         AllPrecedingUsesFromBlockHoisted(&I)) {
       TotalSpeculationCost += Cost;
       if (TotalSpeculationCost > SpecExecMaxSpeculationCost)