Pipe potentially invalid InstructionCost through CodeMetrics

Per the documentation in Support/InstructionCost.h, the purpose of an invalid cost is so that clients can change behavior on impossible to cost inputs. CodeMetrics was instead asserting that invalid costs never occurred.

On a target with an incomplete cost model - e.g. RISCV - this means that transformations would crash on (falsely) invalid constructs - e.g. scalable vectors. While we certainly should improve the cost model - and I plan to do so in the near future - we also shouldn't be crashing. This violates the explicitly stated purpose of an invalid InstructionCost.

I updated all of the "easy" consumers where bailouts were locally obvious. I plan to follow up with loop unroll in a following change.

Differential Revision: https://reviews.llvm.org/D127131

1 files changed, 3 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/CodeMetrics.cpp b/llvm/lib/Analysis/CodeMetrics.cpp
index 97de497..6d90842 100644
--- a/llvm/lib/Analysis/CodeMetrics.cpp
+++ b/llvm/lib/Analysis/CodeMetrics.cpp
@@ -117,13 +117,6 @@ void CodeMetrics::analyzeBasicBlock(
     const BasicBlock *BB, const TargetTransformInfo &TTI,
     const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO) {
   ++NumBlocks;
-  // 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.
@@ -183,8 +176,7 @@ void CodeMetrics::analyzeBasicBlock(
       if (InvI->cannotDuplicate())
         notDuplicatable = true;
 
-    NumInstsProxy += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
-    NumInsts = *NumInstsProxy.getValue();
+    NumInsts += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
   }
 
   if (isa<ReturnInst>(BB->getTerminator()))
@@ -204,6 +196,6 @@ void CodeMetrics::analyzeBasicBlock(
   notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
 
   // Remember NumInsts for this BB.
-  InstructionCost NumInstsThisBB = NumInstsProxy - NumInstsBeforeThisBB;
-  NumBBInsts[BB] = *NumInstsThisBB.getValue();
+  InstructionCost NumInstsThisBB = NumInsts - NumInstsBeforeThisBB;
+  NumBBInsts[BB] = NumInstsThisBB;
 }