NFC: Migrate CodeMetrics 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/D96030

Author: sdesmalen-arm

llvm/lib/Analysis/CodeMetrics.cpp

@@ -18,6 +18,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Function.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/InstructionCost.h"
 
 #define DEBUG_TYPE "code-metrics"
 
@@ -112,7 +113,14 @@ void CodeMetrics::analyzeBasicBlock(
     const BasicBlock *BB, const TargetTransformInfo &TTI,
     const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO) {
   ++NumBlocks;
-  unsigned NumInstsBeforeThisBB = NumInsts;
+  // Use a proxy variable for NumInsts of type InstructionCost, so that it can
+  // use InstructionCost's arithmetic properties such as saturation when this
+  // feature is added to InstructionCost.
+  // When storing the value back to NumInsts, we can assume all costs are Valid
+  // because the IR should not contain any nodes that cannot be costed. If that
+  // happens the cost-model is broken.
+  InstructionCost NumInstsProxy = NumInsts;
+  InstructionCost NumInstsBeforeThisBB = NumInsts;
   for (const Instruction &I : *BB) {
     // Skip ephemeral values.
     if (EphValues.count(&I))
@@ -171,7 +179,8 @@ void CodeMetrics::analyzeBasicBlock(
       if (InvI->cannotDuplicate())
         notDuplicatable = true;
 
-    NumInsts += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
+    NumInstsProxy += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
+    NumInsts = *NumInstsProxy.getValue();
   }
 
   if (isa<ReturnInst>(BB->getTerminator()))
@@ -191,5 +200,6 @@ void CodeMetrics::analyzeBasicBlock(
   notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
 
   // Remember NumInsts for this BB.
-  NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
+  InstructionCost NumInstsThisBB = NumInstsProxy - NumInstsBeforeThisBB;
+  NumBBInsts[BB] = *NumInstsThisBB.getValue();
 }