[GlobalISel] Fix enumeration of entry basic blocks when using GlobalISel

[matejam]

Summary

IRTranslator's method runOnMachineFunction is used to translate from IR to MIR when using GlobalISel as an instruction selector.
When all IR instructions are translated, we move all the instructions from the current entry block to it's only successor, which leaves the current entry block empty and useless, we then delete it from the machine function.
The only issue is that the surviving entry block's number is greater by 1 than the minimal entry block number, which is fixed by assigning the number of the deleted entry block to the surviving entry block's number.
Entry blocks should be serialized (starting from 0) so that an entry block's number wouldn't be greater than the size of the machine function (number of entry blocks in the MF) in which it resides.
Specifically an error will occur in MIRParserImpl::initializeCallSiteInfo when asked if the call site's block number (1 without this patch, 0 with this patch) is greater or equal to the number of entry blocks (1, because the second entry block has been removed).

[arsenm]

Why is a new entry block added in the first place?

llvm/test/CodeGen/X86/rename-new-entry.ll

3

stop-after=irtranslator. This also doesn't need to use a temporary file and should directly pipe to FIleCheck

12–15

Remove these and move triple to llc argument list

24

Remove these comments

45–49

Don't need this metadata

[djtodoro]

LGTM, thanks. The motivation is D87903?

[djtodoro]

Please investigate the test failures.
($ make check-all)

[matejam]

Alternative:
https://reviews.llvm.org/D88667

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

NewEntryBB.splice(NewEntryBB.begin(), EntryBB, EntryBB->begin(),
                     EntryBB->end());
 
   // Update the live-in information for the new entry block.
   for (const MachineBasicBlock::RegisterMaskPair &LiveIn : EntryBB->liveins())
     NewEntryBB.addLiveIn(LiveIn);
   NewEntryBB.sortUniqueLiveIns();
 
   // Get rid of the now empty basic block.
+  int EntryBBNumber = EntryBB->getNumber();
   EntryBB->removeSuccessor(&NewEntryBB);
   MF->remove(EntryBB);
   MF->DeleteMachineBasicBlock(EntryBB);
+  NewEntryBB.setNumber(EntryBBNumber);
 
   assert(&MF->front() == &NewEntryBB &&
          "New entry wasn't next in the list of basic block!");
 
   // Initialize stack protector information.
   StackProtector &SP = getAnalysis<StackProtector>();
   SP.copyToMachineFrameInfo(MF->getFrameInfo());
 
   return false;
 }

llvm/test/CodeGen/X86/rename-new-entry.ll

+;; Test if the entry basic block names start with bb.0.entry when using
+;; GlobalISel
+; RUN: llc -global-isel %s -stop-after=finalize-isel -o %t.mir
+; RUN: cat %t.mir | FileCheck %s
+; CHECK: name: fn1
+; CHECK: bb.0.entry:
+; CHECK: name: fn3
+; CHECK: bb.0.entry:
+; CHECK: name: fn2
+; CHECK: bb.0.entry:
+
+; ModuleID = 'test/CodeGen/X86/rename-new-entry.c'
+source_filename = "test/CodeGen/X86/rename-new-entry.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i32 @fn1(i32 %a) local_unnamed_addr {
+entry:
+  %c = add i32 %a, 2
+  ret i32 %c
+}
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i32 @fn3(i32 %a, i32 %b, i32 %c) local_unnamed_addr {
+entry:
+  %d = add i32 %a, %b
+  %e = mul i32 %d, %c
+  %f = call i32 @fn1(i32 %e)
+  ret i32 %f
+}
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i64 @fn2(i32 %a, i32 %b, i32 %c) local_unnamed_addr {
+entry:
+  %call = call i32 @fn1(i32 5)
+  %add = mul i32 %a, 3
+  %sub = sub i32 %add, %b
+  %add2 = add i32 %sub, %c
+  %conv4 = sext i32 %add2 to i64
+  %call2 = call i32 @fn3(i32 5, i32 %add2, i32 %add2)
+  ret i64 %conv4
+}
+
+!llvm.module.flags = !{!0}
+!llvm.ident = !{!1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"clang version 9.0.0"}