[llvm] r297805 - [BranchFolding] Merge debug locations from common tail instead of removing
Taewook Oh via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 14 22:44:59 PDT 2017
Author: twoh
Date: Wed Mar 15 00:44:59 2017
New Revision: 297805
URL: http://llvm.org/viewvc/llvm-project?rev=297805&view=rev
Log:
[BranchFolding] Merge debug locations from common tail instead of removing
Summary: D25742 improved the precision of debug locations for PGO by removing debug locations from common tail when tail-merging. However, if identical insturctions that are merged into a common tail have the same debug locations, there's no need to remove them. This patch creates a merged debug location of identical instructions across SameTails and assign it to the instruction in the common tail, so that the debug locations are maintained if they are same across identical instructions.
Reviewers: aprantl, probinson, MatzeB, rob.lougher
Reviewed By: aprantl
Subscribers: andreadb, llvm-commits
Differential Revision: https://reviews.llvm.org/D30226
Added:
llvm/trunk/test/CodeGen/X86/tail-merge-debugloc.ll
Modified:
llvm/trunk/lib/CodeGen/BranchFolding.cpp
llvm/trunk/lib/CodeGen/BranchFolding.h
Modified: llvm/trunk/lib/CodeGen/BranchFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BranchFolding.cpp?rev=297805&r1=297804&r2=297805&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.cpp (original)
+++ llvm/trunk/lib/CodeGen/BranchFolding.cpp Wed Mar 15 00:44:59 2017
@@ -32,6 +32,7 @@
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
@@ -753,6 +754,45 @@ bool BranchFolder::CreateCommonTailOnlyB
return true;
}
+/// MergeCommonTailDebugLocs - Create merged DebugLocs of identical instructions
+/// across SameTails and assign it to the instruction in common tail.
+void BranchFolder::MergeCommonTailDebugLocs(unsigned commonTailIndex) {
+ MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+ std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
+ for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
+ if (i != commonTailIndex)
+ NextCommonInsts[i] = SameTails[i].getTailStartPos();
+ else {
+ assert(SameTails[i].getTailStartPos() == MBB->begin() &&
+ "MBB is not a common tail only block");
+ }
+ }
+
+ for (auto &MI : *MBB) {
+ if (MI.isDebugValue())
+ continue;
+ DebugLoc DL = MI.getDebugLoc();
+ for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
+ if (i == commonTailIndex)
+ continue;
+
+ auto &Pos = NextCommonInsts[i];
+ assert(Pos != SameTails[i].getBlock()->end() &&
+ "Reached BB end within common tail");
+ while (Pos->isDebugValue()) {
+ ++Pos;
+ assert(Pos != SameTails[i].getBlock()->end() &&
+ "Reached BB end within common tail");
+ }
+ assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
+ DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
+ NextCommonInsts[i] = ++Pos;
+ }
+ MI.setDebugLoc(DL);
+ }
+}
+
static void
mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
MachineBasicBlock &MBBCommon) {
@@ -905,10 +945,8 @@ bool BranchFolder::TryTailMergeBlocks(Ma
// Recompute common tail MBB's edge weights and block frequency.
setCommonTailEdgeWeights(*MBB);
- // Remove the original debug location from the common tail.
- for (auto &MI : *MBB)
- if (!MI.isDebugValue())
- MI.setDebugLoc(DebugLoc());
+ // Merge debug locations across identical instructions for common tail
+ MergeCommonTailDebugLocs(commonTailIndex);
// MBB is common tail. Adjust all other BB's to jump to this one.
// Traversal must be forwards so erases work.
Modified: llvm/trunk/lib/CodeGen/BranchFolding.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BranchFolding.h?rev=297805&r1=297804&r2=297805&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.h (original)
+++ llvm/trunk/lib/CodeGen/BranchFolding.h Wed Mar 15 00:44:59 2017
@@ -153,6 +153,7 @@ namespace llvm {
MachineBasicBlock *SuccBB,
unsigned maxCommonTailLength,
unsigned &commonTailIndex);
+ void MergeCommonTailDebugLocs(unsigned commonTailIndex);
bool OptimizeBranches(MachineFunction &MF);
bool OptimizeBlock(MachineBasicBlock *MBB);
Added: llvm/trunk/test/CodeGen/X86/tail-merge-debugloc.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/tail-merge-debugloc.ll?rev=297805&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/tail-merge-debugloc.ll (added)
+++ llvm/trunk/test/CodeGen/X86/tail-merge-debugloc.ll Wed Mar 15 00:44:59 2017
@@ -0,0 +1,42 @@
+; RUN: llc -stop-after=branch-folder < %s | FileCheck %s
+;
+; bb2 and bb3 in the IR below will be tail-merged into a single basic block.
+; As br instructions in bb2 and bb3 have the same debug location, make sure that
+; the branch instruction in the merged basic block still maintains the debug
+; location info.
+;
+; CHECK: [[DLOC:![0-9]+]] = !DILocation(line: 2, column: 2, scope: !{{[0-9]+}})
+; CHECK: TEST64rr{{.*}}%rsi, %rsi, implicit-def %eflags
+; CHECK-NEXT: JNE_1{{.*}}, debug-location [[DLOC]]
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @foo(i1 %b, i8* %p) {
+bb1:
+ br i1 %b, label %bb2, label %bb3
+
+bb2:
+ %a1 = icmp eq i8* %p, null
+ br i1 %a1, label %bb4, label %bb5, !dbg !6
+
+bb3:
+ %a2 = icmp eq i8* %p, null
+ br i1 %a2, label %bb4, label %bb5, !dbg !6
+
+bb4:
+ ret i32 1
+
+bb5:
+ ret i32 0
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
+!1 = !DIFile(filename: "foo.c", directory: "b/")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
+!5 = distinct !DILexicalBlock(scope: !4, file: !1, line: 1, column: 1)
+!6 = !DILocation(line: 2, column: 2, scope: !5)
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