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, 7 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index 6dd5f6b..0f33559 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -310,7 +310,13 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
                    L->dump());
         return Rotated;
       }
-      if (Metrics.NumInsts > MaxHeaderSize) {
+      if (!Metrics.NumInsts.isValid()) {
+        LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains instructions"
+                   " with invalid cost: ";
+                   L->dump());
+        return Rotated;
+      }
+      if (*Metrics.NumInsts.getValue() > MaxHeaderSize) {
         LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains "
                           << Metrics.NumInsts
                           << " instructions, which is more than the threshold ("