[PATCH] D97571: [AArch64] Fix emitting an AdrpAddLdr LOH when there's a potential clobber of the def of the adrp before the ldr.

[Amara Emerson via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGb783aa897956: [AArch64] Fix emitting an AdrpAddLdr LOH when there's a potential clobber of the (authored by aemerson).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97571/new/

https://reviews.llvm.org/D97571

Files:
  llvm/lib/Target/AArch64/AArch64CollectLOH.cpp
  llvm/test/CodeGen/AArch64/loh-adrp-add-ldr-clobber.mir


Index: llvm/test/CodeGen/AArch64/loh-adrp-add-ldr-clobber.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/loh-adrp-add-ldr-clobber.mir
@@ -0,0 +1,30 @@
+# RUN: llc -o /dev/null %s -mtriple=aarch64-apple-ios -run-pass=aarch64-collect-loh -debug-only=aarch64-collect-loh 2>&1 | FileCheck %s
+--- |
+  @sym2 = local_unnamed_addr global [10000000 x i32] zeroinitializer, align 8
+  @sym = local_unnamed_addr global i32 zeroinitializer, align 8
+
+  define i32 @main() {
+    ret i32 0
+  }
+
+...
+---
+name:            main
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x22', virtual-reg: '' }
+  - { reg: '$x21', virtual-reg: '' }
+body:             |
+  bb.0:
+    liveins: $x21, $x22
+    ; Check we don't emit an loh here because there's a clobbering def of x8 before the ldr.
+    ; CHECK-LABEL: main
+    ; CHECK-NOT: MCLOH_AdrpAddLdr
+    renamable $x8 = ADRP target-flags(aarch64-page) @sym
+    renamable $x9 = ADDXri killed renamable $x8, target-flags(aarch64-pageoff, aarch64-nc) @sym, 0
+    renamable $x8 = ADDXri killed renamable $x22, 1, 0
+    $x9 = LDRXui $x9, 0
+    RET undef $lr
+
+...
Index: llvm/lib/Target/AArch64/AArch64CollectLOH.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64CollectLOH.cpp
+++ llvm/lib/Target/AArch64/AArch64CollectLOH.cpp
@@ -419,13 +419,37 @@
         ++NumADRPToLDR;
       }
       break;
-    case MCLOH_AdrpAddLdr:
+    case MCLOH_AdrpAddLdr: {
+      // There is a possibility that the linker may try to rewrite:
+      // adrp x0, @sym at PAGE
+      // add x1, x0, @sym at PAGEOFF
+      // [x0 = some other def]
+      // ldr x2, [x1]
+      //    ...into...
+      // adrp x0, @sym
+      // nop
+      // [x0 = some other def]
+      // ldr x2, [x0]
+      // ...if the offset to the symbol won't fit within a literal load.
+      // This causes the load to use the result of the adrp, which in this
+      // case has already been clobbered.
+      // FIXME: Implement proper liveness tracking for all registers. For now,
+      // don't emit the LOH if there are any instructions between the add and
+      // the ldr.
+      MachineInstr *AddMI = const_cast<MachineInstr *>(Info.MI1);
+      const MachineInstr *LdrMI = Info.MI0;
+      auto AddIt = MachineBasicBlock::iterator(AddMI);
+      auto EndIt = AddMI->getParent()->end();
+      if (AddMI->getIterator() == EndIt || LdrMI != &*next_nodbg(AddIt, EndIt))
+        break;
+
       LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAddLdr:\n"
                         << '\t' << MI << '\t' << *Info.MI1 << '\t'
                         << *Info.MI0);
       AFI.addLOHDirective(MCLOH_AdrpAddLdr, {&MI, Info.MI1, Info.MI0});
       ++NumADDToLDR;
       break;
+    }
     case MCLOH_AdrpAddStr:
       if (Info.MI1 != nullptr) {
         LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAddStr:\n"


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