AArch64LoadStoreOptimizer: Correctly clear kill flags

[MatzeB]

Summary

When promoting the Load of a Store-Load pair to a COPY all kill flags
between the store and the load need to be cleared.

[gberry]

LGTM

llvm/trunk/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

if (UnscaledLdOffset == UnscaledStOffset) {
           BuildMI(*LoadI->getParent(), LoadI, LoadI->getDebugLoc(),
                   TII->get(IsStoreXReg ? AArch64::UBFMXri : AArch64::UBFMWri),
                   DestReg)
               .addReg(StRt)
               .addImm(Immr)
               .addImm(Imms);
     }
   }
-  StoreI->clearRegisterKills(StRt, TRI);
 
-  (void)BitExtMI;
+  // Clear kill flags between store and load.
+  for (MachineInstr &MI : make_range(StoreI->getIterator(),
+                                     BitExtMI->getIterator()))
+    MI.clearRegisterKills(StRt, TRI);
 
   DEBUG(dbgs() << "Promoting load by replacing :\n    ");
   DEBUG(StoreI->print(dbgs()));
   DEBUG(dbgs() << "    ");
   DEBUG(LoadI->print(dbgs()));
   DEBUG(dbgs() << "  with instructions:\n    ");
   DEBUG(StoreI->print(dbgs()));
   DEBUG(dbgs() << "    ");

llvm/trunk/test/CodeGen/AArch64/ldst-opt.mir

 # RUN: llc -mtriple=aarch64--linux-gnu -run-pass=aarch64-ldst-opt %s -verify-machineinstrs -o - 2>&1 | FileCheck %s
---- |
-  define void @promote-load-from-store() { ret void }
-  define void @store-pair() { ret void }
-  define void @store-pair-clearkill0() { ret void }
-  define void @store-pair-clearkill1() { ret void }
-...
 ---
 name: promote-load-from-store
 tracksRegLiveness: true
 body: |
   bb.0:
     liveins: %w1, %x0, %lr
 
     STRWui killed %w1, %x0, 0 :: (store 4)

 # CHECK: %w2 = COPY %w1
 # CHECK: STPWi killed %w2, %w1, %x0, 0
 
 # CHECK: %w1 = MOVi32imm
 # CHECK: %w2 = MOVi32imm
 # CHECK-NOT: %w2 = COPY killed %w1
 # CHECK: %w2 = COPY %w1
 # CHECK: STPWi %w1, killed %w2, killed %x0, 0
+---
+name: store-load-clearkill
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: %w1
+
+    STRWui %w1, %sp, 0 :: (store 4)
+    %wzr = COPY killed %w1 ; killing use of %w1
+    %w11 = LDRWui %sp, 0 :: (load 4)
+    HINT 0, implicit %w11 ; some use of %w11
+...
+# When replaceing the load of a store-load pair with a copy the kill flags
+# along the way need to be cleared.
+# CHECK-LABEL: name: store-load-clearkill
+# CHECK: STRWui %w1, %sp, 0 :: (store 4)
+# CHECK-NOT: COPY killed %w1
+# CHECK: %wzr = COPY %w1
+# CHECK: %w11 = ORRWrs %wzr, %w1, 0
+# CHECK: HINT 0, implicit %w11