From e2818e528b46b24652b7f7fcd89fc95154a61ca8 Mon Sep 17 00:00:00 2001
From: Sumanth Gundapaneni <sgundapa@codeaurora.org>
Date: Mon, 9 Jan 2017 17:45:02 +0000
Subject: [PATCH] In the below scenario, we must be able to skip the a
 DBG_VALUE instruction and remove the dead store.

%vreg0<def> = L2_loadri_io <fi#15>, 0; mem:LD4[%dataF](align=4)
DBG_VALUE %vreg0, %noreg, !"dataF", <!184>; IntRegs:%vreg0
S2_storeri_io <fi#15>, 0, %vreg0; mem:ST4[%dataF]

In reality, this kind of stores are eliminated before Stack Slot Coloring pass,
possibly in instruction lowering

Differential Revision: https://reviews.llvm.org/D26616


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291455 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/StackSlotColoring.cpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/CodeGen/StackSlotColoring.cpp b/lib/CodeGen/StackSlotColoring.cpp
index bae828a2263..234b2043a6a 100644
--- a/lib/CodeGen/StackSlotColoring.cpp
+++ b/lib/CodeGen/StackSlotColoring.cpp
@@ -381,7 +381,6 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
        I != E; ++I) {
     if (DCELimit != -1 && (int)NumDead >= DCELimit)
       break;
-
     int FirstSS, SecondSS;
     if (TII->isStackSlotCopy(*I, FirstSS, SecondSS) && FirstSS == SecondSS &&
         FirstSS != -1) {
@@ -392,12 +391,18 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
     }
 
     MachineBasicBlock::iterator NextMI = std::next(I);
-    if (NextMI == MBB->end()) continue;
+    MachineBasicBlock::iterator ProbableLoadMI = I;
 
     unsigned LoadReg = 0;
     unsigned StoreReg = 0;
     if (!(LoadReg = TII->isLoadFromStackSlot(*I, FirstSS)))
       continue;
+    // Skip the ...pseudo debugging... instructions between a load and store.
+    while ((NextMI != E) && NextMI->isDebugValue()) {
+      ++NextMI;
+      ++I;
+    }
+    if (NextMI == E) continue;
     if (!(StoreReg = TII->isStoreToStackSlot(*NextMI, SecondSS)))
       continue;
     if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
@@ -407,7 +412,7 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
 
     if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
       ++NumDead;
-      toErase.push_back(&*I);
+      toErase.push_back(&*ProbableLoadMI);
     }
 
     toErase.push_back(&*NextMI);