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[Assignment Tracking] Only set module flag if pass modifies a function

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The module flag "debug-info-assignment-tracking" is set by the
declare-to-assign pass to indicate that assignment tracking is enabled. This
patch changes declare-to-assign to only set the flag if it makes a
modification. This lets the compiler avoid doing extra work for no benefit,
such as is currently the case if assignment tracking is requested for a build
with line tables only (-gmlt) or a build without debug info.

Reviewed By: scott.linder

Differential Revision: https://reviews.llvm.org/D144481
This commit is contained in:
OCHyams 2023-02-22 16:29:44 +00:00
parent 80a8e6805a
commit 3e48c8d75d
3 changed files with 59 additions and 4 deletions
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2
llvm/include/llvm/IR/DebugInfo.h
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@ -296,7 +296,7 @@ std::optional<AssignmentInfo> getAssignmentInfo(const DataLayout &DL,
class AssignmentTrackingPass : public PassInfoMixin<AssignmentTrackingPass> {
/// Note: this method does not set the debug-info-assignment-tracking module
/// flag.
void runOnFunction(Function &F);
bool runOnFunction(Function &F);
public:
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);

14
llvm/lib/IR/DebugInfo.cpp
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@ -1963,7 +1963,8 @@ void at::trackAssignments(Function::iterator Start, Function::iterator End,
}
}
void AssignmentTrackingPass::runOnFunction(Function &F) {
bool AssignmentTrackingPass::runOnFunction(Function &F) {
bool Changed = false;
// Collect a map of {backing storage : dbg.declares} (currently "backing
// storage" is limited to Allocas). We'll use this to find dbg.declares to
// delete after running `trackAssignments`.
@ -2016,8 +2017,10 @@ void AssignmentTrackingPass::runOnFunction(Function &F) {
// Delete DDI because the variable location is now tracked using
// assignment tracking.
DDI->eraseFromParent();
Changed = true;
}
}
return Changed;
}
static const char *AssignmentTrackingModuleFlag =
@ -2040,7 +2043,8 @@ bool llvm::isAssignmentTrackingEnabled(const Module &M) {
PreservedAnalyses AssignmentTrackingPass::run(Function &F,
FunctionAnalysisManager &AM) {
runOnFunction(F);
if (!runOnFunction(F))
return PreservedAnalyses::all();
// Record that this module uses assignment tracking. It doesn't matter that
// some functons in the module may not use it - the debug info in those
@ -2056,8 +2060,12 @@ PreservedAnalyses AssignmentTrackingPass::run(Function &F,
PreservedAnalyses AssignmentTrackingPass::run(Module &M,
ModuleAnalysisManager &AM) {
bool Changed = false;
for (auto &F : M)
runOnFunction(F);
Changed |= runOnFunction(F);
if (!Changed)
return PreservedAnalyses::all();
// Record that this module uses assignment tracking.
setAssignmentTrackingModuleFlag(M);

47
llvm/test/DebugInfo/Generic/assignment-tracking/declare-to-assign/set-flag-only-if-modified.ll Normal file
View File

@ -0,0 +1,47 @@
; RUN: opt -passes=declare-to-assign -S %s -o - \
; RUN: | FileCheck %s --check-prefix=WITHOUT-INTRINSIC
; RUN: sed 's/;Uncomment-with-sed//g' < %s \
; RUN: | opt -passes=declare-to-assign -S - -o - \
; RUN: | FileCheck %s --check-prefix=WITH-INTRINSIC
; WITHOUT-INTRINSIC-NOT: "debug-info-assignment-tracking"
; WITH-INTRINSIC: "debug-info-assignment-tracking"
;; Check that the module flag "debug-info-assignment-tracking" is only added if
;; declare-to-assign actually modifies the function. In the first run the
;; dbg.declare is commented out and the pass leaves the function unmodified.
;; In the second run sed is used to uncomment the dbg.declare and
;; declare-to-assign replaces it with a dbg.assign.
define dso_local void @f() !dbg !9 {
entry:
%a = alloca i32, align 4
;Uncomment-with-sed call void @llvm.dbg.declare(metadata ptr %a, metadata !13, metadata !DIExpression()), !dbg !16
ret void, !dbg !17
}
declare void @llvm.dbg.declare(metadata, metadata, metadata)
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3, !4, !5, !6, !7}
!llvm.ident = !{!8}
!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 17.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "test.c", directory: "/")
!2 = !{i32 7, !"Dwarf Version", i32 5}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{i32 1, !"wchar_size", i32 4}
!5 = !{i32 8, !"PIC Level", i32 2}
!6 = !{i32 7, !"PIE Level", i32 2}
!7 = !{i32 7, !"uwtable", i32 2}
!8 = !{!"clang version 17.0.0"}
!9 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !10, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
!10 = !DISubroutineType(types: !11)
!11 = !{null}
!12 = !{!13}
!13 = !DILocalVariable(name: "a", scope: !9, file: !1, line: 1, type: !14)
!14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!15 = !DILocation(line: 1, column: 12, scope: !9)
!16 = !DILocation(line: 1, column: 16, scope: !9)
!17 = !DILocation(line: 1, column: 19, scope: !9)