[llvm] r223401 - Debug info: If the RegisterCoalescer::reMaterializeTrivialDef() is
Adrian Prantl
aprantl at apple.com
Thu Dec 4 15:08:34 PST 2014
> On Dec 4, 2014, at 3:01 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Thu, Dec 4, 2014 at 2:59 PM, Adrian Prantl <aprantl at apple.com> wrote:
>
> > On Dec 4, 2014, at 2:35 PM, David Blaikie <dblaikie at gmail.com> wrote:
> >
> >
> >
> > On Thu, Dec 4, 2014 at 2:29 PM, Adrian Prantl <aprantl at apple.com> wrote:
> > Author: adrian
> > Date: Thu Dec 4 16:29:04 2014
> > New Revision: 223401
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=223401&view=rev
> > Log:
> > Debug info: If the RegisterCoalescer::reMaterializeTrivialDef() is
> > eliminating all uses of a vreg, update any DBG_VALUE describing that vreg
> > to point to the rematerialized register instead.
> >
> > Added:
> > llvm/trunk/test/DebugInfo/AArch64/coalescing.ll
> > Modified:
> > llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
> >
> > Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=223401&r1=223400&r2=223401&view=diff
> > ==============================================================================
> > --- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
> > +++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Thu Dec 4 16:29:04 2014
> > @@ -898,8 +898,20 @@ bool RegisterCoalescer::reMaterializeTri
> >
> > // The source interval can become smaller because we removed a use.
> > LIS->shrinkToUses(&SrcInt, &DeadDefs);
> > - if (!DeadDefs.empty())
> > + if (!DeadDefs.empty()) {
> > + // If the virtual SrcReg is completely eliminated, update all DBG_VALUEs
> > + // to describe DstReg instead.
> > + for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg),
> > + UE = MRI->use_end(); UI != UE; ++UI) {
> >
> > range-for with use_operands?
>
> Updated in r223405. Looks much nicer, thanks!
>
> >
> > + MachineOperand &UseMO = *UI;
> > + MachineInstr *UseMI = UseMO.getParent();
> > + if (UseMI->isDebugValue()) {
> > + UseMO.setReg(DstReg);
> > + DEBUG({dbgs() << "\t\tupdated: " << *UseMI;});
> > + }
> > + }
> > eliminateDeadDefs();
> > + }
> >
> > return true;
> > }
> >
> > Added: llvm/trunk/test/DebugInfo/AArch64/coalescing.ll
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/AArch64/coalescing.ll?rev=223401&view=auto
> > ==============================================================================
> > --- llvm/trunk/test/DebugInfo/AArch64/coalescing.ll (added)
> > +++ llvm/trunk/test/DebugInfo/AArch64/coalescing.ll Thu Dec 4 16:29:04 2014
> > @@ -0,0 +1,70 @@
> > +; RUN: llc -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
> > +;
> > +; Generated at -Os from:
> > +; void *my_memcpy(void *dst, const void * src, long n);
> > +; void* getBytesNoCopy();
> > +; void start() {
> > +; unsigned size;
> > +; my_memcpy(&size, getBytesNoCopy(), sizeof(size));
> >
> > are all of these parameters needed? Any idea what the interactions are?
> We can safely omit the last two arguments.
>
> Could you remove them & anything else that's not needed to reproduce this issue? (optionally, in addition, I usually find it a bit easier to remove the original source identifiers and just use foo/bar/baz/etc - so that there's no confusion about existing/previous semantics of the functions that aren't relevant to the test)
Sorry, I forgot to mention, I did remove them in r223405, too :-)
>
> >
> > +; if (size != 0) { }
> >
> > Sort of surprised this code isn't DCE'd by -Os?
>
> This is an unrelated, but still interesting bug. If the value isn’t used after the call, we’re dropping the dbg.value entirely. Nevermind that the actual used is still being optimized away.
>
> It'd be nice to leave it out of an unrelated test, so that it's easier to tell what this test is meant to test when code changes affect its results, etc.
Well, I like to put the source code that a testcase was derived from in the comment, and that line *is* necessary to get to the IR in the testcase. I’d rather add a comment than remove the line.
-- adrian
>
>
> >
> > +; }
> > +
> > +; ModuleID = 'test1.cpp'
> > +target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
> > +target triple = "arm64-apple-ios"
> > +
> > +; Function Attrs: nounwind optsize
> > +define void @_Z5startv() #0 {
> > +entry:
> > + %size = alloca i32, align 4
> > + %0 = bitcast i32* %size to i8*, !dbg !15
> > + %call = tail call i8* @_Z14getBytesNoCopyv() #3, !dbg !16
> > + %call1 = call i8* @_Z9my_memcpyPvPKvl(i8* %0, i8* %call, i64 4) #3, !dbg !15
> > + call void @llvm.dbg.value(metadata !{i32* %size}, i64 0, metadata !10, metadata !17), !dbg !18
> > + ; CHECK: .debug_info contents:
> > + ; CHECK: DW_TAG_variable
> > + ; CHECK-NEXT: DW_AT_location
> > + ; CHECK-NEXT: DW_AT_name {{.*}}"size"
> > + ; CHECK: .debug_loc contents:
> > + ; CHECK: Location description: 70 00
> > + ret void, !dbg !19
> > +}
> > +
> > +; Function Attrs: optsize
> > +declare i8* @_Z9my_memcpyPvPKvl(i8*, i8*, i64) #1
> > +
> > +; Function Attrs: optsize
> > +declare i8* @_Z14getBytesNoCopyv() #1
> > +
> > +; Function Attrs: nounwind readnone
> > +declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
> > +
> > +attributes #0 = { nounwind optsize }
> > +attributes #1 = { optsize }
> > +attributes #2 = { nounwind readnone }
> > +attributes #3 = { nounwind optsize }
> > +
> > +!llvm.dbg.cu = !{!0}
> > +!llvm.module.flags = !{!12, !13}
> > +!llvm.ident = !{!14}
> > +
> > +!0 = metadata !{metadata !"0x11\004\00clang version 3.6.0 (trunk 223149) (llvm/trunk 223153)\001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2} ; [ DW_TAG_compile_unit ] [/<stdin>] [DW_LANG_C_plus_plus]
> > +!1 = metadata !{metadata !"<stdin>", metadata !""}
> > +!2 = metadata !{}
> > +!3 = metadata !{metadata !4}
> > +!4 = metadata !{metadata !"0x2e\00start\00start\00_Z5startv\003\000\001\000\000\00256\001\004", metadata !5, metadata !6, metadata !7, null, void ()* @_Z5startv, null, null, metadata !9} ; [ DW_TAG_subprogram ] [line 3] [def] [scope 4] [start]
> > +!5 = metadata !{metadata !"test1.cpp", metadata !""}
> > +!6 = metadata !{metadata !"0x29", metadata !5} ; [ DW_TAG_file_type ] [/test1.cpp]
> > +!7 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !8, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
> > +!8 = metadata !{null}
> > +!9 = metadata !{metadata !10}
> > +!10 = metadata !{metadata !"0x100\00size\005\000", metadata !4, metadata !6, metadata !11} ; [ DW_TAG_auto_variable ] [size] [line 5]
> > +!11 = metadata !{metadata !"0x24\00unsigned int\000\0032\0032\000\000\007", null, null} ; [ DW_TAG_base_type ] [unsigned int] [line 0, size 32, align 32, offset 0, enc DW_ATE_unsigned]
> > +!12 = metadata !{i32 2, metadata !"Dwarf Version", i32 2}
> > +!13 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
> > +!14 = metadata !{metadata !"clang version 3.6.0 (trunk 223149) (llvm/trunk 223153)"}
> > +!15 = metadata !{i32 6, i32 3, metadata !4, null}
> > +!16 = metadata !{i32 6, i32 25, metadata !4, null}
> > +!17 = metadata !{metadata !"0x102"} ; [ DW_TAG_expression ]
> > +!18 = metadata !{i32 5, i32 12, metadata !4, null}
> > +!19 = metadata !{i32 9, i32 1, metadata !4, null}
> >
> >
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