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[CGP] Reset the debug location when promoting zext(s). 

When the zext gets promoted, it used to retain the original location,
which pessimizes the debugging experience causing an unexpected
jump in stepping at -Og.

Fixes https://bugs.llvm.org/show_bug.cgi?id=46120 (which also
contains a full C repro).

Differential Revision:  https://reviews.llvm.org/D81437
This commit is contained in:
Davide Italiano 2020-06-17 10:29:47 -07:00
parent 7c7c8e0da4
commit 1cbaf847ab
3 changed files with 43 additions and 10 deletions
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14
llvm/lib/CodeGen/CodeGenPrepare.cpp
View File

@ -2443,6 +2443,9 @@ namespace {
/// This class provides transaction based operation on the IR.
/// Every change made through this class is recorded in the internal state and
/// can be undone (rollback) until commit is called.
/// CGP does not check if instructions could be speculatively executed when
/// moved. Preserving the original location would pessimize the debugging
/// experience, as well as negatively impact the quality of sample PGO.
class TypePromotionTransaction {
/// This represents the common interface of the individual transaction.
/// Each class implements the logic for doing one specific modification on
@ -2658,6 +2661,7 @@ class TypePromotionTransaction {
ZExtBuilder(Instruction *InsertPt, Value *Opnd, Type *Ty)
: TypePromotionAction(InsertPt) {
IRBuilder<> Builder(InsertPt);
Builder.SetCurrentDebugLocation(DebugLoc());
Val = Builder.CreateZExt(Opnd, Ty, "promoted");
LLVM_DEBUG(dbgs() << "Do: ZExtBuilder: " << *Val << "\n");
}
@ -5798,16 +5802,8 @@ bool CodeGenPrepare::optimizeExt(Instruction *&Inst) {
if (canFormExtLd(SpeculativelyMovedExts, LI, ExtFedByLoad, HasPromoted)) {
assert(LI && ExtFedByLoad && "Expect a valid load and extension");
TPT.commit();
// Move the extend into the same block as the load
// Move the extend into the same block as the load.
ExtFedByLoad->moveAfter(LI);
// CGP does not check if the zext would be speculatively executed when moved
// to the same basic block as the load. Preserving its original location
// would pessimize the debugging experience, as well as negatively impact
// the quality of sample pgo. We don't want to use "line 0" as that has a
// size cost in the line-table section and logically the zext can be seen as
// part of the load. Therefore we conservatively reuse the same debug
// location for the load and the zext.
ExtFedByLoad->setDebugLoc(LI->getDebugLoc());
++NumExtsMoved;
Inst = ExtFedByLoad;
return true;

2
llvm/test/DebugInfo/X86/zextload.ll
View File

@ -23,7 +23,7 @@
; CHECK-LABEL: @test
; CHECK: [[LOADVAL:%[0-9]+]] = load i32, i32* %ptr, align 4, !dbg [[DEBUGLOC:![0-9]+]]
; CHECK-NEXT: zext i32 [[LOADVAL]] to i64, !dbg [[DEBUGLOC]]
; CHECK-NEXT: zext i32 [[LOADVAL]] to i64
; CHECK: [[DEBUGLOC]] = !DILocation(line: 3
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"

37
llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: opt < %s -codegenprepare -S -mtriple=x86_64-unknown-unknown | FileCheck %s --match-full-lines
; Make sure the promoted zext doesn't get a debug location associated.
; CHECK: %promoted = zext i8 %t to i64
define void @patatino(i8* %p, i64* %q, i32 %b, i32* %addr) !dbg !6 {
entry:
%t = load i8, i8* %p, align 1, !dbg !8
%zextt = zext i8 %t to i32, !dbg !9
%add = add nuw i32 %zextt, %b, !dbg !10
%add2 = add nuw i32 %zextt, 12, !dbg !11
store i32 %add, i32* %addr, align 4, !dbg !12
%s = zext i32 %add2 to i64, !dbg !13
store i64 %s, i64* %q, align 4, !dbg !14
ret void, !dbg !15
}
!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!3, !4}
!llvm.module.flags = !{!5}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
!1 = !DIFile(filename: "a2.ll", directory: "/")
!2 = !{}
!3 = !{i32 8}
!4 = !{i32 0}
!5 = !{i32 2, !"Debug Info Version", i32 3}
!6 = distinct !DISubprogram(name: "patatino", linkageName: "patatino", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
!7 = !DISubroutineType(types: !2)
!8 = !DILocation(line: 1, column: 1, scope: !6)
!9 = !DILocation(line: 2, column: 1, scope: !6)
!10 = !DILocation(line: 3, column: 1, scope: !6)
!11 = !DILocation(line: 4, column: 1, scope: !6)
!12 = !DILocation(line: 5, column: 1, scope: !6)
!13 = !DILocation(line: 6, column: 1, scope: !6)
!14 = !DILocation(line: 7, column: 1, scope: !6)
!15 = !DILocation(line: 8, column: 1, scope: !6)