[llvm-bugs] [Bug 48724] SROA causing invalid code generation

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48724

Nuno Lopes <nunoplopes at sapo.pt> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |---
             Status|RESOLVED                    |REOPENED

--- Comment #2 from Nuno Lopes <nunoplopes at sapo.pt> ---
Let me take a step back as the story is a bit more complicated.
SROA tries to be smart in recovering the type information in the structures,
but ends up missing bits that are memcpy'ed. This data is memcpy'ed from
padding bits, but we don't have any rule saying it's illegal to memcpy to/from
padding (we do have for load/stores, though). We may want to patch LangRef
instead of fixing SROA?


Reduced test case:

target datalayout =
"e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%CallArg = type { %"[]u8" }
%"[]u8" = type { i8*, i64 }
%ExpressionResult = type { i64, i1 }

@0 = internal unnamed_addr constant [20 x i8] c"what happened to me\00", align
1
@1 = internal unnamed_addr constant %CallArg { %"[]u8" { i8* getelementptr
inbounds ([20 x i8], [20 x i8]* @0, i64 0, i64 0), i64 19 } }, align 8

declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8*
noalias nocapture readonly, i64, i1 immarg) #0

define void @main() {
  %v.i = alloca %"[]u8", align 8
  %w.i = alloca %"[]u8", align 8
  %result = alloca %ExpressionResult, align 8
  %derp = alloca %ExpressionResult, align 8

  ; copy @1 -> %v.1
  %x3 = getelementptr inbounds %CallArg, %CallArg* @1, i32 0, i32 0
  %x7 = bitcast %"[]u8"* %x3 to i8*
  %x8 = bitcast %"[]u8"* %v.i to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x8, i8* %x7, i64 16, i1 false)

  ; copy %v.1 -> %result
  %x14 = bitcast %ExpressionResult* %result to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x14, i8* %x8, i64 16, i1 false)

  ; copy %result -> %w.i
  %x18 = bitcast %"[]u8"* %w.i to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x18, i8* %x14, i64 16, i1 false)

  ; output %w.i
  call void @std.os.write(i32 1, %"[]u8"* %w.i)
  ret void

SwitchProng1.i3:                                  ; No predecessors!
  %x35 = getelementptr inbounds %ExpressionResult, %ExpressionResult* %derp,
i32 0, i32 1
  store i1 false, i1* %x35, align 1
  ret void

SwitchProng2.i4:                                  ; No predecessors!
  %x37 = bitcast %ExpressionResult* %result to i8*
  %x38 = bitcast %ExpressionResult* %derp to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x38, i8* %x37, i64 24, i1 false)
  ret void
}

declare void @std.os.write(i32, %"[]u8"*)

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