[llvm] [RISCV] Stack clash protection for dynamic alloca (PR #122508)

[Craig Topper via llvm-commits]

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@@ -545,6 +545,16 @@ void RISCVFrameLowering::allocateAndProbeStackForRVV(
       .addReg(SPReg)
       .addReg(TargetReg)
       .setMIFlag(Flag);
+
+  // If we have a dynamic allocation later we need to probe any residuals.
+  MachineBasicBlock *NextMBB = MBBI->getParent()->getSingleSuccessor();
+  if (NextMBB && NextMBB->begin()->getFlag(MachineInstr::FrameSetup)) {
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topperc wrote:

If understand correctly, this is trying to find the expansion of the `RISCV::PROBED_STACKALLOC_DYN`? What guarantees that would be the first BB after the prologue. Couldn't there be other control flow before it?

https://github.com/llvm/llvm-project/pull/122508