[PATCH] D71192: AMDGPU: Fix AMDGPUUnifyDivergentExitNodes with no normal returns

[Connor Abbott via Phabricator via llvm-commits]

cwabbott created this revision.
cwabbott added reviewers: arsenm, nhaehnle, critson.
Herald added subscribers: llvm-commits, hiraditya, t-tye, tpr, dstuttard, yaxunl, wdng, jvesely, kzhuravl.
Herald added a project: LLVM.
cwabbott added a parent revision: D70781: AMDGPU: Fix handling of infinite loops in fragment shaders.

The code was assuming in a few places that if there was only one exit
from the function that it was a normal return, which is invalid. It
could be an infinite loop, in which case we still need to insert the
usual fake edge so that the null export happens. This fixes shaders that
end with an infinite loop that discards.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71192

Files:
  llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
  llvm/test/CodeGen/AMDGPU/kill-infinite-loop.ll


Index: llvm/test/CodeGen/AMDGPU/kill-infinite-loop.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/kill-infinite-loop.ll
+++ llvm/test/CodeGen/AMDGPU/kill-infinite-loop.ll
@@ -45,6 +45,22 @@
   ret void
 }
 
+; test the case where there's only a kill in an infinite loop
+; CHECK-LABEL: only_kill
+; CHECK: exp null off, off, off, off done vm
+; CHECK-NEXT: s_endpgm
+; SIInsertSkips inserts an extra null export here, but it should be harmless.
+; CHECK: exp null off, off, off, off done vm
+; CHECK-NEXT: s_endpgm
+define amdgpu_ps void @only_kill() #0 {
+main_body:
+  br label %loop
+
+loop:
+  call void @llvm.amdgcn.kill(i1 false) #3
+  br label %loop
+}
+
 ; In case there's an epilog, we shouldn't have to do this.
 ; CHECK-LABEL: return_nonvoid
 ; CHECK-NOT: exp null off, off, off, off done vm
Index: llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
@@ -195,8 +195,6 @@
 
 bool AMDGPUUnifyDivergentExitNodes::runOnFunction(Function &F) {
   auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
-  if (PDT.getRoots().size() <= 1)
-    return false;
 
   LegacyDivergenceAnalysis &DA = getAnalysis<LegacyDivergenceAnalysis>();
 
@@ -321,7 +319,7 @@
   if (ReturningBlocks.empty())
     return false; // No blocks return
 
-  if (ReturningBlocks.size() == 1)
+  if (ReturningBlocks.size() == 1 && !InsertExport)
     return false; // Already has a single return block
 
   const TargetTransformInfo &TTI


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