[TailRecursionElimination] Skip debug intrinsics.

[fhahn]

Summary

I think we do not need to analyze debug intrinsics here, as they should
not impact codegen. This has 2 benefits: 1) slightly less work to do and

2. avoiding generating optimization remarks for converting calls to

debug intrinsics to tail calls, which are not really helpful for users.

Based on work by Sander de Smalen.

[aprantl]

Seems reasonable!

[davide]

No objections on my side.

lib/Transforms/Scalar/TailRecursionElimination.cpp

static bool markTails(Function &F, bool &AllCallsAreTailCalls,
   BasicBlock *BB = &F.getEntryBlock();
   VisitType Escaped = UNESCAPED;
   do {
     for (auto &I : *BB) {
       if (Tracker.EscapePoints.count(&I))
         Escaped = ESCAPED;
 
       CallInst *CI = dyn_cast<CallInst>(&I);
-      if (!CI || CI->isTailCall())
+      if (!CI || CI->isTailCall() || isa<DbgInfoIntrinsic>(&I))
         continue;
 
       bool IsNoTail = CI->isNoTailCall() || CI->hasOperandBundles();
 
       if (!IsNoTail && CI->doesNotAccessMemory()) {
         // A call to a readnone function whose arguments are all things computed
         // outside this function can be marked tail. Even if you stored the
         // alloca address into a global, a readnone function can't load the

test/Transforms/MergeFunc/mergefunc-preserve-debug-info.ll

 ; OPTIMIZATION_LEVEL_0-NEXT: store i32 %y, i32* %y.addr, align 4
 ; OPTIMIZATION_LEVEL_0-NEXT: call void @llvm.dbg.declare(metadata i32* %y.addr, metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_0-NEXT: %0 = tail call i32 @maxA(i32 %x, i32 %y), !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_0-NEXT: ret i32 %0, !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_0-NEXT: }
 
 ; OPTIMIZATION_LEVEL_2: define i32 @maxB(i32 %x, i32 %y)
 ; OPTIMIZATION_LEVEL_2-NEXT: entry:
-; OPTIMIZATION_LEVEL_2-NEXT: tail call void @llvm.dbg.value(metadata i32 %x, metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
-; OPTIMIZATION_LEVEL_2-NEXT: tail call void @llvm.dbg.value(metadata i32 %y, metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
+; OPTIMIZATION_LEVEL_2-NEXT: call void @llvm.dbg.value(metadata i32 %x, metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
+; OPTIMIZATION_LEVEL_2-NEXT: call void @llvm.dbg.value(metadata i32 %y, metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_2-NEXT: %0 = tail call i32 @maxA(i32 %x, i32 %y) #{{[0-9]+}}, !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_2-NEXT: ret i32 %0, !dbg !{{[0-9]+}}
 ; OPTIMIZATION_LEVEL_2-NEXT: }
 
 entry:
   %x.addr = alloca i32, align 4
   %y.addr = alloca i32, align 4
   %i = alloca i32, align 4