[AArch64] Keep track of MIFlags in the LoadStoreOptimizer

[thegameg]

Summary

Merging:

• $x26, $x25 = frame-setup LDPXi $sp, 0
• $sp = frame-destroy ADDXri $sp, 64, 0

into an LDPXpost should preserve the flags from both instructions as following:

• frame-setup frame-destroy LDPXpost

[junbuml]

test/CodeGen/AArch64/ldst-miflags.mir

8

It would be good to have one more test case for non-pair case like LDRXui.

[junbuml]

Should we do this only in mergeUpdateInsn? What about other merges like mergePairedInsns ?

[thegameg]

Handle (hopefully) all the different cases.

lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

AArch64LoadStoreOpt::mergeUpdateInsn(MachineBasicBlock::iterator I,
   MachineInstrBuilder MIB;
   if (!isPairedLdSt(*I)) {
     // Non-paired instruction.
     MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
               .add(getLdStRegOp(*Update))
               .add(getLdStRegOp(*I))
               .add(getLdStBaseOp(*I))
               .addImm(Value)
-              .setMemRefs(I->memoperands_begin(), I->memoperands_end());
+              .setMemRefs(I->memoperands_begin(), I->memoperands_end())
+              .setMIFlags(I->getFlags() | Update->getFlags());
   } else {
     // Paired instruction.
     int Scale = getMemScale(*I);
     MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
               .add(getLdStRegOp(*Update))
               .add(getLdStRegOp(*I, 0))
               .add(getLdStRegOp(*I, 1))
               .add(getLdStBaseOp(*I))
               .addImm(Value / Scale)
-              .setMemRefs(I->memoperands_begin(), I->memoperands_end());
+              .setMemRefs(I->memoperands_begin(), I->memoperands_end())
+              .setMIFlags(I->getFlags() | Update->getFlags());
   }
   (void)MIB;
 
   if (IsPreIdx) {
     ++NumPreFolded;
     DEBUG(dbgs() << "Creating pre-indexed load/store.");
   } else {
     ++NumPostFolded;

test/CodeGen/AArch64/ldst-miflags.mir

+# RUN: llc -run-pass=aarch64-ldst-opt -o - -mtriple=aarch64-- %s | FileCheck %s
+#
+---
+name:            foo
+# CHECK-LABEL: name: foo
+body:             |
+  bb.0:
+    $x26, $x25 = frame-setup LDPXi $sp, 0
+    $sp = frame-destroy ADDXri $sp, 64, 0
+
+  ; Check that we merge the MIFlags from both the instructions in the final
+  ; instruction.
+  ; CHECK: = frame-setup frame-destroy LDPXpost
+    RET_ReallyLR