[llvm-branch-commits] [llvm] [ARM][Thumb1] Verify EstimateFunctionSizeInBytes every time (PR #203319)

[Peter Smith via llvm-branch-commits]

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@@ -511,6 +511,36 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) {
 
   LLVM_DEBUG(dbgs() << '\n'; dumpBBs());
 
+  if (auto Estimate = AFI->getEstimatedFunctionSizeInBytes()) {
+    auto RealSize = BBUtils->getFunctionSize();
+    if (RealSize > *Estimate) {
+      LLVM_DEBUG({
+        dbgs() << "ARMConstantIslandsPass output for " << mf.getName()
+               << " with sizes:\n";
+        for (MachineBasicBlock &MBB : mf) {
+          unsigned Offset = BBUtils->getOffsetOf(&MBB);
+          unsigned End = BBUtils->getBBInfo()[MBB.getNumber()].postOffset();
+          dbgs() << printMBBReference(MBB) << ": // offset "
+                 << Twine::utohexstr(Offset) << "\n";
+          for (MachineInstr &MI : MBB) {
+            unsigned InstSize = TII->getInstSizeInBytes(MI);
+            LLVM_DEBUG(dbgs() << "    0x" << Twine::utohexstr(Offset) << " +"
+                              << InstSize << ": " << MI);
+            Offset += InstSize;
+          }
+          if (Offset < End) {
+            LLVM_DEBUG(dbgs() << "    0x" << Twine::utohexstr(Offset) << " +"
+                              << (End - Offset) << ": extra\n");
+          }
+        }
+      });
+      report_fatal_error(
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smithp35 wrote:

Would a `-mllvm` level command-line option to disable this error be worthwhile? I'm thinking that we may be unconditionally breaking programs that while their size is underestimated, currently compile successfully.

The other thing we could do is make it a warning, which would be irritating enough to report the problem, but would allow the program to build. 

https://github.com/llvm/llvm-project/pull/203319