[llvm] [llvm][ARM] Add a cortex-m4f alignment hazard recognizer (PR #126991)

[Oliver Stannard via llvm-commits]

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@@ -5455,6 +5473,21 @@ bool ARMBaseInstrInfo::hasNOP() const {
   return Subtarget.hasFeature(ARM::HasV6KOps);
 }
 
+void ARMBaseInstrInfo::insertNoop(MachineBasicBlock &MBB,
+                                  MachineBasicBlock::iterator MI) const {
+  DebugLoc DL;
+  if (hasNOP()) {
+    BuildMI(MBB, MI, DL, get(ARM::HINT)).addImm(0).addImm(ARMCC::AL).addImm(0);
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ostannard wrote:

This is an ARM instruction, you probably need to check the target architecture and emit the correct one. Also, this is a 32-bit instruction, so won't change the halfword alignment, but thumb does have a 16-bit NOP you can use (and 16-bit MOV for targets which don't have it).

https://github.com/llvm/llvm-project/pull/126991