[llvm] a8f36cc - [AArch64] Check Subtarget via STI in getInstSizeInBytes (#192089)

[via llvm-commits]

Author: Zachary Yedidia
Date: 2026-04-14T10:59:19-07:00
New Revision: a8f36ccb2a24ef4abcbff58b2f36ce2deacefd54

URL: https://github.com/llvm/llvm-project/commit/a8f36ccb2a24ef4abcbff58b2f36ce2deacefd54
DIFF: https://github.com/llvm/llvm-project/commit/a8f36ccb2a24ef4abcbff58b2f36ce2deacefd54.diff

LOG: [AArch64] Check Subtarget via STI in getInstSizeInBytes (#192089)

The InstSizes test (`llvm/unittests/Target/AArch64/InstSizes.cpp`)
destroys the Subtarget field early (`ST` created on the stack in
[`createInstrInfo`](https://github.com/llvm/llvm-project/blob/40a585e742ed6b28306d7511380079325ba1a003/llvm/unittests/Target/AArch64/InstSizes.cpp#L32)),
causing a use-after-free if it is used in `getInstSizeInBytes`. This
causes a failure when running the test with hwasan (reported by build
bot). To fix this, this PR switches to using `STI` instead of
`Subtarget` in `getInstSizeInBytes` for checking `isLFI`, which survives
for the lifetime of the test.

I think fixing the test itself (the root of the issue, as far as I can
tell) would be more involved. Perhaps I should open an issue for it
though?

I have tested the fix on an AArch64 machine with hwasan to confirm that
it resolves the issue.

Added: 
    

Modified: 
    llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index 3ca851ef83d27..9d805dad07c1c 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -151,7 +151,8 @@ unsigned AArch64InstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
   const MCInstrDesc &Desc = MI.getDesc();
 
   // LFI rewriter expansions that supersede normal sizing.
-  if (Subtarget.isLFI())
+  const auto &STI = MF->getSubtarget<AArch64Subtarget>();
+  if (STI.isLFI())
     if (auto Size = getLFIInstSizeInBytes(MI))
       return *Size;
 
@@ -162,7 +163,6 @@ unsigned AArch64InstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
     if (!MFI->shouldSignReturnAddress(*MF))
       return NumBytes;
 
-    const auto &STI = MF->getSubtarget<AArch64Subtarget>();
     auto Method = STI.getAuthenticatedLRCheckMethod(*MF);
     NumBytes += AArch64PAuth::getCheckerSizeInBytes(Method);
     return NumBytes;