DwarfDebug: Emit number of bytes in .debug_loc entry directly

Emit the number of bytes in a `.debug_loc` entry directly.  The old code
created temp labels (expensive), emitted the difference between them,
and then emitted one on each side of the relevant bytes.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`
(the optimized version of ld64's `-save-temps` when linking the
`verify-uselistorder` executable in an LTO bootstrap).  I've hacked
`MCContext::Allocate()` to just call `malloc()` instead of using the
`BumpPtrAllocator` so that the heap profile is easier to read.  As far
as peak memory is concerned, `MCContext::Allocate()` is equivalent to a
leak, since it only gets freed at process teardown.

In my heap profile, this patch drops memory usage of
`DwarfDebug::emitDebugLoc()` from 132.56 MB (11.4%) down to 29.86 MB
(2.7%) at peak memory.  Some of that must be noise from `SmallVector`
(or other) allocations -- peak memory only dropped from 1160 MB down to
1100 MB -- but this nevertheless shaves 5% off the top.)

llvm-svn: 236629

4 files changed, 7 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 4fe4f26c923..e275d3aac7d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1545,16 +1545,13 @@ void DebugLocEntry::finalize(const AsmPrinter &AP, DebugLocStream &Locs,
 }
 
 void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry) {
+  // Emit the size.
   Asm->OutStreamer->AddComment("Loc expr size");
-  MCSymbol *begin = Asm->OutStreamer->getContext().CreateTempSymbol();
-  MCSymbol *end = Asm->OutStreamer->getContext().CreateTempSymbol();
-  Asm->EmitLabelDifference(end, begin, 2);
-  Asm->OutStreamer->EmitLabel(begin);
+  Asm->EmitInt16(DebugLocs.getBytes(Entry).size());
+
   // Emit the entry.
   APByteStreamer Streamer(*Asm);
   emitDebugLocEntry(Streamer, Entry);
-  // Close the range.
-  Asm->OutStreamer->EmitLabel(end);
 }
 
 // Emit locations into the debug loc section.
diff --git a/llvm/test/CodeGen/X86/2010-05-25-DotDebugLoc.ll b/llvm/test/CodeGen/X86/2010-05-25-DotDebugLoc.ll
index e14365ac848..3b99e91915f 100644
--- a/llvm/test/CodeGen/X86/2010-05-25-DotDebugLoc.ll
+++ b/llvm/test/CodeGen/X86/2010-05-25-DotDebugLoc.ll
@@ -2,8 +2,7 @@
 ; RUN: llc -mtriple=x86_64-pc-linux -O2 -regalloc=basic < %s | FileCheck %s
 ; Test to check .debug_loc support. This test case emits many debug_loc entries.
 
-; CHECK: .short {{.*}} # Loc expr size
-; CHECK-NEXT: .Ltmp
+; CHECK: .short 1 # Loc expr size
 ; CHECK-NEXT: DW_OP_reg
 
 %0 = type { double }
diff --git a/llvm/test/CodeGen/X86/2010-05-26-DotDebugLoc.ll b/llvm/test/CodeGen/X86/2010-05-26-DotDebugLoc.ll
index 788853e4308..3670c556aa7 100644
--- a/llvm/test/CodeGen/X86/2010-05-26-DotDebugLoc.ll
+++ b/llvm/test/CodeGen/X86/2010-05-26-DotDebugLoc.ll
@@ -77,18 +77,12 @@ declare void @llvm.dbg.value(metadata, i64, metadata, metadata) nounwind readnon
 ; CHECK-NEXT: .quad   [[SET1]]
 ; CHECK-NEXT: [[SET2:.*]] = [[LABEL]]-Lfunc_begin0
 ; CHECK-NEXT: .quad   [[SET2]]
-; CHECK-NEXT: Lset{{.*}} = Ltmp{{.*}}-Ltmp{{.*}}               ## Loc expr size
-; CHECK-NEXT: .short  Lset{{.*}}
-; CHECK-NEXT: Ltmp{{.*}}:
+; CHECK-NEXT: .short  1     ## Loc expr size
 ; CHECK-NEXT: .byte   85
-; CHECK-NEXT: Ltmp{{.*}}:
 ; CHECK-NEXT: [[SET3:.*]] = [[LABEL]]-Lfunc_begin0
 ; CHECK-NEXT: .quad   [[SET3]]
 ; CHECK-NEXT: [[SET4:.*]] = [[CLOBBER]]-Lfunc_begin0
 ; CHECK-NEXT: .quad   [[SET4]]
-; CHECK-NEXT: Lset{{.*}} = Ltmp{{.*}}-Ltmp{{.*}}               ## Loc expr size
-; CHECK-NEXT: .short  Lset{{.*}}
-; CHECK-NEXT: Ltmp{{.*}}:
+; CHECK-NEXT: .short  1     ## Loc expr size
 ; CHECK-NEXT: .byte   83
-; CHECK-NEXT: Ltmp{{.*}}:
 !38 = !{i32 1, !"Debug Info Version", i32 3}
diff --git a/llvm/test/DebugInfo/X86/dbg-value-range.ll b/llvm/test/DebugInfo/X86/dbg-value-range.ll
index fcde006320d..a8fa9073fa7 100644
--- a/llvm/test/DebugInfo/X86/dbg-value-range.ll
+++ b/llvm/test/DebugInfo/X86/dbg-value-range.ll
@@ -55,11 +55,8 @@ declare void @llvm.dbg.value(metadata, i64, metadata, metadata) nounwind readnon
 ;CHECK-NEXT:	.quad
 ;CHECK-NEXT: [[CLOBBER_OFF:Lset.*]] = [[CLOBBER]]-{{.*}}
 ;CHECK-NEXT:	.quad	[[CLOBBER_OFF]]
-;CHECK-NEXT: Lset{{.*}} = Ltmp{{.*}}-Ltmp{{.*}}
-;CHECK-NEXT:    .short  Lset
-;CHECK-NEXT: Ltmp
+;CHECK-NEXT:  .short 1 ## Loc expr size
 ;CHECK-NEXT:	.byte	85 ## DW_OP_reg
-;CHECK-NEXT: Ltmp
 ;CHECK-NEXT:	.quad	0
 ;CHECK-NEXT:	.quad	0
 !24 = !{i32 1, !"Debug Info Version", i32 3}