This is a fix for PR# 19051. I noticed code gen differences due to co…

…de motion when running tests with and without the debug info at O2. The problem is in branch folding. A loop wanted to skip the debug info, but actually it didn't do so.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204865 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/BranchFolding.cpp

@@ -1515,7 +1515,7 @@ MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
   // branch from condition setting instruction.
   MachineBasicBlock::iterator PI = Loc;
   --PI;
-  while (PI != MBB->begin() && Loc->isDebugValue())
+  while (PI != MBB->begin() && PI->isDebugValue())
     --PI;
 
   bool IsDef = false;

test/CodeGen/X86/dbg-changes-codegen-branch-folding.ll

@@ -0,0 +1,109 @@
+; RUN: llc -march=x86-64 -mtriple=x86_64-linux < %s | FileCheck %s
+; RUN: opt -strip-debug < %s | llc -march=x86-64 -mtriple=x86_64-linux | FileCheck %s
+; http://llvm.org/PR19051. Minor code-motion difference with -g.
+; Presence of debug info shouldn't affect the codegen. Make sure that
+; we generated the same code sequence with and without debug info. 
+;
+; CHECK:      callq   _Z3fooPcjPKc
+; CHECK:      callq   _Z3fooPcjPKc
+; CHECK:      leaq    (%rsp), %rdi
+; CHECK:      movl    $4, %esi
+; CHECK:      testl   {{%[a-z]+}}, {{%[a-z]+}}
+; CHECK:      je     .LBB0_4
+
+; Regenerate test with this command: 
+;   clang -emit-llvm -S -O2 -g
+; from this source:
+;
+; extern void foo(char *dst,unsigned siz,const char *src);
+; extern const char * i2str(int);
+;
+; struct AAA3 {
+;  AAA3(const char *value) { foo(text,sizeof(text),value);}
+;  void operator=(const char *value) { foo(text,sizeof(text),value);}
+;  operator const char*() const { return text;}
+;  char text[4];
+; };
+;
+; void bar (int param1,int param2)  {
+;   const char * temp(0);
+;
+;   if (param2) {
+;     temp = i2str(param2);
+;   }
+;   AAA3 var1("");
+;   AAA3 var2("");
+;
+;   if (param1)
+;     var2 = "+";
+;   else
+;     var2 = "-";
+;   var1 = "";
+; }
+
+%struct.AAA3 = type { [4 x i8] }
+
+@.str = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+@.str1 = private unnamed_addr constant [2 x i8] c"+\00", align 1
+@.str2 = private unnamed_addr constant [2 x i8] c"-\00", align 1
+
+; Function Attrs: uwtable
+define void @_Z3barii(i32 %param1, i32 %param2) #0 {
+entry:
+  %var1 = alloca %struct.AAA3, align 1
+  %var2 = alloca %struct.AAA3, align 1
+  %tobool = icmp eq i32 %param2, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call = call i8* @_Z5i2stri(i32 %param2)
+  br label %if.end
+
+if.end:                                           ; preds = %entry, %if.then
+  call void @llvm.dbg.value(metadata !{%struct.AAA3* %var1}, i64 0, metadata !60)
+  call void @llvm.dbg.value(metadata !62, i64 0, metadata !63)
+  %arraydecay.i = getelementptr inbounds %struct.AAA3* %var1, i64 0, i32 0, i64 0
+  call void @_Z3fooPcjPKc(i8* %arraydecay.i, i32 4, i8* getelementptr inbounds ([1 x i8]* @.str, i64 0, i64 0))
+  call void @llvm.dbg.declare(metadata !{%struct.AAA3* %var2}, metadata !38)
+  %arraydecay.i5 = getelementptr inbounds %struct.AAA3* %var2, i64 0, i32 0, i64 0
+  call void @_Z3fooPcjPKc(i8* %arraydecay.i5, i32 4, i8* getelementptr inbounds ([1 x i8]* @.str, i64 0, i64 0))
+  %tobool1 = icmp eq i32 %param1, 0
+  br i1 %tobool1, label %if.else, label %if.then2
+
+if.then2:                                         ; preds = %if.end
+  call void @_Z3fooPcjPKc(i8* %arraydecay.i5, i32 4, i8* getelementptr inbounds ([2 x i8]* @.str1, i64 0, i64 0))
+  br label %if.end3
+
+if.else:                                          ; preds = %if.end
+  call void @_Z3fooPcjPKc(i8* %arraydecay.i5, i32 4, i8* getelementptr inbounds ([2 x i8]* @.str2, i64 0, i64 0))
+  br label %if.end3
+
+if.end3:                                          ; preds = %if.else, %if.then2
+  call void @_Z3fooPcjPKc(i8* %arraydecay.i, i32 4, i8* getelementptr inbounds ([1 x i8]* @.str, i64 0, i64 0))
+  ret void
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata) #1
+
+declare i8* @_Z5i2stri(i32) #2
+
+declare void @_Z3fooPcjPKc(i8*, i32, i8*) #2
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata) #1
+
+attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+attributes #2 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.module.flags = !{!48, !49}
+!llvm.ident = !{!50}
+
+!38 = metadata !{i32 786688, null, metadata !"var2", null, i32 20, null, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [var2] [line 20]
+!48 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!49 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
+!50 = metadata !{metadata !"clang version 3.5 (202418)"}
+!60 = metadata !{i32 786689, null, metadata !"this", null, i32 16777216, null, i32 1088, null} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!62 = metadata !{i8* getelementptr inbounds ([1 x i8]* @.str, i64 0, i64 0)}
+!63 = metadata !{i32 786689, null, metadata !"value", null, i32 33554439, null, i32 0, null} ; [ DW_TAG_arg_variable ] [value] [line 7]