[MergeFuncs] Use sizeWithoutDebug for canCreateThunkFor

I noticed that when we determine the size of the function to figure out if its profitable, we include debug instructions which can end up making larger functions than necessary.

Author: oskarwirga

llvm/lib/Transforms/IPO/MergeFunctions.cpp

@@ -653,7 +653,7 @@ static bool canCreateThunkFor(Function *F) {
   // Don't merge tiny functions using a thunk, since it can just end up
   // making the function larger.
   if (F->size() == 1) {
-    if (F->front().size() <= 2) {
+    if (F->front().sizeWithoutDebug() < 2) {
       LLVM_DEBUG(dbgs() << "canCreateThunkFor: " << F->getName()
                         << " is too small to bother creating a thunk for\n");
       return false;

llvm/test/Transforms/MergeFunc/no-merge-debug-thunks.ll

@@ -0,0 +1,61 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+;; Make sure debug instructions are not counted when deciding to merge functions
+; RUN: opt -S -passes=mergefunc < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+; Function Attrs: nounwind readnone
+define hidden i32 @f(i32 %t) {
+; CHECK-LABEL: define hidden i32 @f
+; CHECK-SAME: (i32 [[T:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[T]], metadata [[META6:![0-9]+]], metadata !DIExpression()), !dbg [[DBG12:![0-9]+]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[T]], metadata [[META6]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  call void @llvm.dbg.value(metadata i32 %t, metadata !12, metadata !DIExpression()), !dbg !13
+  call void @llvm.dbg.value(metadata i32 %t, metadata !12, metadata !DIExpression()), !dbg !13
+  ret i32 0
+}
+
+; Function Attrs: nounwind readnone
+define hidden i32 @f_thunk(i32 %t) {
+; CHECK-LABEL: define hidden i32 @f_thunk
+; CHECK-SAME: (i32 [[T:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[T]], metadata [[META6]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[T]], metadata [[META6]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  call void @llvm.dbg.value(metadata i32 %t, metadata !12, metadata !DIExpression()), !dbg !13
+  call void @llvm.dbg.value(metadata i32 %t, metadata !12, metadata !DIExpression()), !dbg !13
+  ret i32 0
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "no-merge-debug-thunks.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "t", arg: 1, scope: !7, file: !1, line: 3, type: !10)
+!13 = !DILocation(line: 3, column: 14, scope: !7)
+!14 = !DILocation(line: 4, column: 12, scope: !7)
+!16 = distinct !DISubprogram(name: "_start", scope: !1, file: !1, line: 7, type: !17, isLocal: false, isDefinition: true, scopeLine: 7, isOptimized: true, unit: !0, retainedNodes: !2)
+!17 = !DISubroutineType(types: !18)
+!18 = !{!10}
+!19 = !DILocation(line: 8, column: 3, scope: !16)
+!20 = !DILocation(line: 9, column: 3, scope: !16)