[llvm] r288794 - [framelowering] Improve tracking of first CS pop instruction.

[Florian Hahn via llvm-commits]

Hi Greg,

Thanks for pointing me to the issue, I¹ll have a look.

Cheers,
Florian

--



From:  Greg Bedwell <gregbedwell at gmail.com>
Date:  Thursday, 8 December 2016 at 20:11
To:  Florian Hahn <Florian.Hahn at arm.com>
Cc:  "llvm-commits at lists.llvm.org" <llvm-commits at lists.llvm.org>
Subject:  Re: [llvm] r288794 - [framelowering] Improve tracking of first
CS pop instruction.


Hi Florian,

In our testing using the clang/utils/check_cfc tool we spotted a case
where after this commit we're seeing a new codegen difference depending on
whether or not -g is specified.  I've put the details in PR31319 (
https://llvm.org/bugs/show_bug.cgi?id=31319 ).

Thanks,

-Greg Bedwell
SN Systems Ltd - Sony Interactive Entertainment



On 6 December 2016 at 10:24, Florian Hahn via llvm-commits
<llvm-commits at lists.llvm.org> wrote:

Author: fhahn
Date: Tue Dec  6 04:24:55 2016
New Revision: 288794

URL: 
http://llvm.org/viewvc/llvm-project?rev=288794&view=rev
<http://llvm.org/viewvc/llvm-project?rev=288794&view=rev>
Log:
[framelowering] Improve tracking of first CS pop instruction.


Summary: This patch makes sure FirstCSPop and MBBI never point to
DBG_VALUE instructions, which affected the code generated.

Reviewers: mkuper, aprantl, MatzeB

Subscribers: llvm-commits

Differential Revision:
https://reviews.llvm.org/D27343 <https://reviews.llvm.org/D27343>

Added:
    llvm/trunk/test/CodeGen/X86/frame-lowering-debug-intrinsic.ll
Modified:
    llvm/trunk/lib/Target/X86/X86FrameLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
URL: 
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLower
ing.cpp?rev=288794&r1=288793&r2=288794&view=diff
<http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLowe
ring.cpp?rev=288794&r1=288793&r2=288794&view=diff>
===========================================================================
===
--- llvm/trunk/lib/Target/X86/X86FrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86FrameLowering.cpp Tue Dec  6 04:24:55 2016
@@ -1550,19 +1550,22 @@ void X86FrameLowering::emitEpilogue(Mach
   }
   uint64_t SEHStackAllocAmt = NumBytes;

+  MachineBasicBlock::iterator FirstCSPop = MBBI;
   // Skip the callee-saved pop instructions.
   while (MBBI != MBB.begin()) {
     MachineBasicBlock::iterator PI = std::prev(MBBI);
     unsigned Opc = PI->getOpcode();

-    if ((Opc != X86::POP32r || !PI->getFlag(MachineInstr::FrameDestroy))
&&
-        (Opc != X86::POP64r || !PI->getFlag(MachineInstr::FrameDestroy))
&&
-        Opc != X86::DBG_VALUE && !PI->isTerminator())
-      break;
+    if (Opc != X86::DBG_VALUE && !PI->isTerminator()) {
+      if ((Opc != X86::POP32r ||
!PI->getFlag(MachineInstr::FrameDestroy)) &&
+          (Opc != X86::POP64r ||
!PI->getFlag(MachineInstr::FrameDestroy)))
+        break;
+      FirstCSPop = PI;
+    }

     --MBBI;
   }
-  MachineBasicBlock::iterator FirstCSPop = MBBI;
+  MBBI = FirstCSPop;

   if (TargetMBB) {
     // Fill EAX/RAX with the address of the target block.

Added: llvm/trunk/test/CodeGen/X86/frame-lowering-debug-intrinsic.ll
URL: 
http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/frame-lower
ing-debug-intrinsic.ll?rev=288794&view=auto
<http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/frame-lowe
ring-debug-intrinsic.ll?rev=288794&view=auto>
===========================================================================
===
--- llvm/trunk/test/CodeGen/X86/frame-lowering-debug-intrinsic.ll (added)
+++ llvm/trunk/test/CodeGen/X86/frame-lowering-debug-intrinsic.ll Tue Dec
6 04:24:55 2016
@@ -0,0 +1,41 @@
+; Test ensuring debug intrinsics do not affect generated function
prologue.
+;
+; RUN: llc -O1 -mtriple=x86_64-unknown-unknown -o - %s | FileCheck %s
+
+
+define i64 @noDebug(i64 %a) {
+  %call = call i64 @fn(i64 %a, i64 0)
+  ret i64 %call
+}
+
+; CHECK-LABEL: noDebug
+; CHECK: popq %rcx
+; CHECK: ret
+
+
+define i64 @withDebug(i64 %a) !dbg !4 {
+  %call = call i64 @fn(i64 %a, i64 0)
+  tail call void @llvm.dbg.value(metadata i64 %call, i64 0, metadata !5,
metadata !6), !dbg !7
+  ret i64 %call
+}
+
+; CHECK-LABEL: withDebug
+; CHECK: popq %rcx
+; CHECK: ret
+
+
+declare i64 @fn(i64, i64)
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu <http://llvm.dbg.cu> = !{!0}
+!llvm.module.flags = !{!2,!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer:
"clang version 4.0.0")
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "withDebug", unit: !0)
+!5 = !DILocalVariable(name: "w", scope: !4)
+!6 = !DIExpression()
+!7 = !DILocation(line: 210, column: 12, scope: !4)


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