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

1 files changed, 2 insertions, 8 deletions

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}