[Arm] Fix UAF in ARMConstantIslandPass

[qinkunbao]

#146198 changes

    for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
      BRChange |= fixupImmediateBr(ImmBranches[i]);

to

    for (ImmBranch &Br : ImmBranches)
      BRChange |= fixupImmediateBr(Br);

Unfortunately, they are not NFC and cause the buildbot error. e.g.,
https://lab.llvm.org/buildbot/#/builders/24/builds/9943
https://lab.llvm.org/buildbot/#/builders/169/builds/12570
Use make_early_inc_range to fix the issue

[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: Qinkun Bao (qinkunbao)

Changes

#146198 changes

    for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
      BRChange |= fixupImmediateBr(ImmBranches[i]);

to

    for (ImmBranch &Br : ImmBranches)
      BRChange |= fixupImmediateBr(Br);

Unfortunately, they are not NFC and causes the buildbot error. e.g.,
https://lab.llvm.org/buildbot/#/builders/24/builds/9943
https://lab.llvm.org/buildbot/#/builders/169/builds/12570
Revoke the change to fix the bot.

---

Full diff: https://github.com/llvm/llvm-project/pull/146232.diff

1 Files Affected:

• (modified) llvm/lib/Target/ARM/ARMConstantIslandPass.cpp (+2-2)

diff --git a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
index e72aa8ef051cd..ca3dc15ff3ad6 100644
--- a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -476,8 +476,8 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) {
 
     LLVM_DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');
     bool BRChange = false;
-    for (ImmBranch &Br : ImmBranches)
-      BRChange |= fixupImmediateBr(Br);
+    for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
+      BRChange |= fixupImmediateBr(ImmBranches[i]);
     if (BRChange && ++NoBRIters > 30)
       report_fatal_error("Branch Fix Up pass failed to converge!");
     LLVM_DEBUG(dumpBBs());

[kazutakahirata]

LGTM. Thanks!

[arsenm]

I'm assuming this is fixupImmediateBr resizing the vector, can you use make_early_inc_range

[qinkunbao]

Looks like it does not work.
@thurstond FYI