[BPF] fix a CO-RE issue with -mattr=+alu32

Ilya Leoshkevich (<iii@linux.ibm.com>) reported an issue that
with -mattr=+alu32 CO-RE has a segfault in BPF MISimplifyPatchable
pass.

The pattern will be transformed by MISimplifyPatchable
pass looks like below:
  r5 = ld_imm64 @"b:0:0$0:0"
  r2 = ldw r5, 0
  ... r2 ... // use r2
The pass will remove the intermediate 'ldw' instruction
and replacing all r2 with r5 likes below:
  r5 = ld_imm64 @"b:0:0$0:0"
  ... r5 ... // use r5
Later, the ld_imm64 insn will be replaced with
  r5 = <patched immediate>
for field relocation purpose.

With -mattr=+alu32, the input code may become
  r5 = ld_imm64 @"b:0:0$0:0"
  w2 = ldw32 r5, 0
  ... w2 ... // use w2
Replacing "w2" with "r5" is incorrect and will
trigger compiler internal errors.

To fix the problem, if the register class of ldw* dest
register is sub_32, we just replace the original ldw*
register with:
  w2 = w5
Directly replacing all uses of w2 with in-place
constructed w5 for the use operand seems not working in all cases.

The latest kernel will have -mattr=+alu32 on by default,
so added this flag to all CORE tests.
Tested with latest kernel bpf-next branch as well with this patch.

Differential Revision: https://reviews.llvm.org/D69438

1 files changed, 10 insertions, 5 deletions

diff --git a/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp b/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
index 9c689aed641..d21b977af90 100644
--- a/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
+++ b/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
@@ -124,11 +124,16 @@ bool BPFMISimplifyPatchable::removeLD() {
       if (!IsCandidate)
         continue;
 
-      auto Begin = MRI->use_begin(DstReg), End = MRI->use_end();
-      decltype(End) NextI;
-      for (auto I = Begin; I != End; I = NextI) {
-        NextI = std::next(I);
-        I->setReg(SrcReg);
+      if (MRI->getRegClass(DstReg) == &BPF::GPR32RegClass) {
+        BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(BPF::COPY), DstReg)
+            .addReg(SrcReg, 0, BPF::sub_32);
+      } else {
+        auto Begin = MRI->use_begin(DstReg), End = MRI->use_end();
+        decltype(End) NextI;
+        for (auto I = Begin; I != End; I = NextI) {
+          NextI = std::next(I);
+          I->setReg(SrcReg);
+        }
       }
 
       ToErase = &MI;