[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
llvm-svn: 297805
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 08aafda..6654248 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -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 @@
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 @@
// 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.
diff --git a/llvm/lib/CodeGen/BranchFolding.h b/llvm/lib/CodeGen/BranchFolding.h
index 0773a2c..7c756e5 100644
--- a/llvm/lib/CodeGen/BranchFolding.h
+++ b/llvm/lib/CodeGen/BranchFolding.h
@@ -153,6 +153,7 @@
MachineBasicBlock *SuccBB,
unsigned maxCommonTailLength,
unsigned &commonTailIndex);
+ void MergeCommonTailDebugLocs(unsigned commonTailIndex);
bool OptimizeBranches(MachineFunction &MF);
bool OptimizeBlock(MachineBasicBlock *MBB);