From 1a69f7be23c3818fddb0680cb28d66d1b080f8f9 Mon Sep 17 00:00:00 2001
From: Yi-Hong Lyu <Yi-Hong.Lyu@ibm.com>
Date: Fri, 11 Oct 2019 05:32:29 +0000
Subject: [PATCH] [PowerPC] Remove assertion "Shouldn't overwrite a register
 before it is killed"

The assertion is everzealous and fail tests like:

  renamable $x3 = LI8 0
  STD renamable $x3, 16, $x1
  renamable $x3 = LI8 0

Remove the assertion since killed flag of $x3 is not mandentory.

Differential Revision: https://reviews.llvm.org/D68344

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374515 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/PowerPC/PPCPreEmitPeephole.cpp     | 17 +++++++-------
 .../PowerPC/remove-redundant-load-imm.mir     | 22 +++++++++++++++++++
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/lib/Target/PowerPC/PPCPreEmitPeephole.cpp b/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
index 1de01f9bcbc..b1c0433641d 100644
--- a/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
+++ b/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
@@ -117,8 +117,6 @@ namespace {
 
           if (!AfterBBI->modifiesRegister(Reg, TRI))
             continue;
-          assert(DeadOrKillToUnset &&
-                 "Shouldn't overwrite a register before it is killed");
           // Finish scanning because Reg is overwritten by a non-load
           // instruction.
           if (AfterBBI->getOpcode() != Opc)
@@ -134,12 +132,15 @@ namespace {
           // It loads same immediate value to the same Reg, which is redundant.
           // We would unset kill flag in previous Reg usage to extend live range
           // of Reg first, then remove the redundancy.
-          LLVM_DEBUG(dbgs() << " Unset dead/kill flag of " << *DeadOrKillToUnset
-                            << " from " << *DeadOrKillToUnset->getParent());
-          if (DeadOrKillToUnset->isDef())
-            DeadOrKillToUnset->setIsDead(false);
-          else
-            DeadOrKillToUnset->setIsKill(false);
+          if (DeadOrKillToUnset) {
+            LLVM_DEBUG(dbgs()
+                       << " Unset dead/kill flag of " << *DeadOrKillToUnset
+                       << " from " << *DeadOrKillToUnset->getParent());
+            if (DeadOrKillToUnset->isDef())
+              DeadOrKillToUnset->setIsDead(false);
+            else
+              DeadOrKillToUnset->setIsKill(false);
+          }
           DeadOrKillToUnset =
               AfterBBI->findRegisterDefOperand(Reg, true, true, TRI);
           if (DeadOrKillToUnset)
diff --git a/test/CodeGen/PowerPC/remove-redundant-load-imm.mir b/test/CodeGen/PowerPC/remove-redundant-load-imm.mir
index 02db2caa1e7..1dd37955452 100644
--- a/test/CodeGen/PowerPC/remove-redundant-load-imm.mir
+++ b/test/CodeGen/PowerPC/remove-redundant-load-imm.mir
@@ -346,3 +346,25 @@ body:             |
     BLR8 implicit $lr8, implicit $rm
 
 ...
+---
+name:            overwrite_reg_before_killed
+alignment:       16
+tracksRegLiveness: true
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $x1
+
+    ; CHECK-LABEL: name: overwrite_reg_before_killed
+    ; CHECK: liveins: $x1
+    ; CHECK: renamable $x3 = LI8 0
+    ; CHECK: STD renamable $x3, 16, $x1
+    ; CHECK: STD killed renamable $x3, 8, $x1
+    ; CHECK: BLR8 implicit $lr8, implicit $rm
+    renamable $x3 = LI8 0
+    STD renamable $x3, 16, $x1
+    renamable $x3 = LI8 0
+    STD killed renamable $x3, 8, $x1
+    BLR8 implicit $lr8, implicit $rm
+
+...
-- 
2.40.0