AArch64: remove all kill flags when extending register liveness.

When we forward a stored value to a load and eliminate it entirely we need to
make sure the liveness of the register is maintained all the way to its use.
Previously we only cleared liveness on the store doing the forwarding, but
there could be other killing uses in between.

We already do the right thing when the load has to be converted into something
else, it was just this one path that skipped it.

llvm-svn: 306318

2 files changed, 26 insertions, 1 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
index c45c0b4c8ed..005f2d51e40 100644
--- a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
@@ -808,7 +808,13 @@ AArch64LoadStoreOpt::promoteLoadFromStore(MachineBasicBlock::iterator LoadI,
     // Remove the load, if the destination register of the loads is the same
     // register for stored value.
     if (StRt == LdRt && LoadSize == 8) {
-      StoreI->clearRegisterKills(StRt, TRI);
+      for (MachineInstr &MI : make_range(StoreI->getIterator(),
+                                         LoadI->getIterator())) {
+        if (MI.killsRegister(StRt, TRI)) {
+          MI.clearRegisterKills(StRt, TRI);
+          break;
+        }
+      }
       DEBUG(dbgs() << "Remove load instruction:\n    ");
       DEBUG(LoadI->print(dbgs()));
       DEBUG(dbgs() << "\n");
diff --git a/llvm/test/CodeGen/AArch64/ldst-opt.mir b/llvm/test/CodeGen/AArch64/ldst-opt.mir
index 5b3576d898e..9cb9528cc62 100644
--- a/llvm/test/CodeGen/AArch64/ldst-opt.mir
+++ b/llvm/test/CodeGen/AArch64/ldst-opt.mir
@@ -162,3 +162,22 @@ body: |
 # CHECK: UBFMWri undef %w1
 # CHECK: STRHHui undef %w3
 # CHECK: ANDWri undef %w3
+---
+name: promote-load-from-store-trivial-kills
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: %x0, %lr
+
+    STRXui %x0, %sp, 0 :: (store 8)
+    STRXui killed %x0, %sp, 2 :: (store 8)
+    %x0 = LDRXui %sp, 0 :: (load 8)
+    BL $bar, csr_aarch64_aapcs, implicit-def %lr, implicit %sp, implicit %x0, implicit-def %sp
+    RET %lr
+...
+# CHECK-LABEL: name: promote-load-from-store-trivial-kills
+# CHECK: STRXui %x0, %sp, 0
+# CHECK: STRXui %x0, %sp, 2
+# CHECK-NOT: LDRXui
+# CHECK-NOT: ORR
+# CHECK: BL $bar, csr_aarch64_aapcs, implicit-def %lr, implicit %sp, implicit %x0, implicit-def %sp