[llvm-bugs] [Bug 31811] New: return value propagation in asm/naked function

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31811

            Bug ID: 31811
           Summary: return value propagation in asm/naked function
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: ck at remobjects.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The null propagation code should not propagate function results for naked
functions as else it's impossible to have asm code that returns it's own value:

When having a naked function like:
; Function Attrs: naked noinline optnone
define i32 @callcatch(i32, i32) #3 !dbg !10103 {
BasicBlock8472:
  call void asm "\0D\0Apushl %ebp\0D\0Amovl 8(%esp),%eax\0D\0Amovl 12(%esp),
%ebp\0D\0Acalll *%eax\0D\0Apopl %ebp\0D\0Aretl\0D\0A", ""(), !dbg !10104,
!srcloc !10106 // this returns in eax
  ret i32 0, !dbg !10104
}

; Function Attrs: naked noinline optnone
define void @jumptocont(i32, i32, i32) #3 !dbg !10107 {
BasicBlock8473:
  call void asm "\0D\0A    movl 12(%esp), %ebp\0D\0A    movl 4(%esp),
%eax\0D\0A    movl 8(%esp), %esp\0D\0A    jmpl *%eax\0D\0A", ""(), !dbg !10108,
!srcloc !10110
  ret void, !dbg !10108
}

and calling code is like;
  %530 = call i32 @callcatch(i32 %528, i32 %529) #3, !dbg !7648
  store i32 %530, i32* %20, !dbg !7648
  %531 = load i32, i32* %20, !dbg !7630
...
  call void @jumptocont(i32 %531, i32 %532, i32 %533) #3, !dbg

However the return constant propagation code from

http://llvm.org/docs/doxygen/html/IPConstantPropagation_8cpp_source.html

finds the ret i32 0 and ends up calling jumptocont with i32 0 as a first
parameter, which wasn't what I wanted. Ending up like:

 %189 = tail call i32 @callcatchn(i32 %188, i32 %12) #10, !dbg !7019
  tail call void @jumptocont(i32 0, i32 %14, i32 %12) #10, !dbg !7022 

ie using the ret i32 0 as input for jumptocont, which it shouldn't.

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