[llvm] [AMDGPU] Improve amdgcn_kill verification (PR #208220)

[Robert Imschweiler via llvm-commits]

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@@ -144,9 +144,13 @@ void llvm::verifyAMDGPUIntrinsicCall(VerifierSupport &VS, Intrinsic::ID ID,
     if (auto *CBI = dyn_cast<CallBrInst>(&Call)) {
       Check(CBI->getNumIndirectDests() == 1,
             "callbr amdgcn_kill only supports one indirect dest");
-      bool Unreachable = isa<UnreachableInst>(CBI->getIndirectDest(0)->begin());
-      CallInst *CI = dyn_cast<CallInst>(CBI->getIndirectDest(0)->begin());
-      Check(Unreachable ||
+      // We assume that amdgcn_unreachable is only introduced by
+      // AMDGPUUnifyDivergentExitNodes, which replaces the block's original
+      // unreachable terminator by a call to amdgcn_unreachable + a return.
+      const Instruction *Term = CBI->getIndirectDest(0)->getTerminator();
+      const CallInst *CI =
+          Term ? dyn_cast_if_present<CallInst>(Term->getPrevNode()) : nullptr;
+      Check(isa_and_nonnull<UnreachableInst>(Term) ||
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ro-i wrote:

> But the special was already here. I'm not sure I see what this actually changes

It fixes the verification. Because AMDGPUUnifyDivergentExitNodes isn't inserting amdgcn_unreachable as the first instruction, but rather as the first before the new return (both replace the unreachable)

https://github.com/llvm/llvm-project/pull/208220