[llvm] 63b0227 - [Attributor][NFCI] Avoid spending time resolving kernel reachability queries

[Johannes Doerfert via llvm-commits]

Author: Johannes Doerfert
Date: 2023-02-02T13:59:58-08:00
New Revision: 63b02271a8916c8ed8ce240ac5823825329755a6

URL: https://github.com/llvm/llvm-project/commit/63b02271a8916c8ed8ce240ac5823825329755a6
DIFF: https://github.com/llvm/llvm-project/commit/63b02271a8916c8ed8ce240ac5823825329755a6.diff

LOG: [Attributor][NFCI] Avoid spending time resolving kernel reachability queries

We know kernels (generally) cannot be called from within the module. Thus,
for reachability we would need to step back from a kernel which would allow
us to reach anything anyway. Even if a kernel is invoked from another
kernel, values like allocas and shared memory are not accessible. We
implicitly check for this situation to avoid costly lookups.

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/Attributor.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 67d21adb6bdb..f83acb0f1753 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -586,6 +586,19 @@ isPotentiallyReachable(Attributor &A, const Instruction &FromI,
         dbgs() << *ES << "\n";
   });
 
+  // We know kernels (generally) cannot be called from within the module. Thus,
+  // for reachability we would need to step back from a kernel which would allow
+  // us to reach anything anyway. Even if a kernel is invoked from another
+  // kernel, values like allocas and shared memory are not accessible. We
+  // implicitly check for this situation to avoid costly lookups.
+  if (GoBackwardsCB && &ToFn != FromI.getFunction() &&
+      !GoBackwardsCB(*FromI.getFunction()) && ToFn.hasFnAttribute("kernel") &&
+      FromI.getFunction()->hasFnAttribute("kernel")) {
+    LLVM_DEBUG(dbgs() << "[AA] assume kernel cannot be reached from within the "
+                         "module; success\n";);
+    return false;
+  }
+
   // If we can go arbitrarily backwards we will eventually reach an entry point
   // that can reach ToI. Only if a set of blocks through which we cannot go is
   // provided, or once we track internal functions not accessible from the