[PATCH] D100988: [FuncAttrs] Don't infer willreturn for nonexact definitions

[Stefan Stipanovic via Phabricator via llvm-commits]

sstefan1 created this revision.
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Discovered during attributor testing comparing stats with
and without the attributor. Willreturn should not be inferred
for nonexact definitions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100988

Files:
  llvm/lib/Transforms/IPO/FunctionAttrs.cpp
  llvm/test/Transforms/FunctionAttrs/willreturn.ll


Index: llvm/test/Transforms/FunctionAttrs/willreturn.ll
===================================================================
--- llvm/test/Transforms/FunctionAttrs/willreturn.ll
+++ llvm/test/Transforms/FunctionAttrs/willreturn.ll
@@ -153,5 +153,12 @@
   br label %bb1
 }
 
+define linkonce i32 @square(i32) {
+; CHECK-NOT: Function Attrs: {{.*}}willreturn
+; CHECK: define linkonce i32 @square(
+    %2 = mul nsw i32 %0, %0
+    ret i32 %2
+}
+
 declare i64 @fn_noread() readnone
 declare void @fn_willreturn() willreturn
Index: llvm/lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1432,6 +1432,12 @@
 }
 
 static bool functionWillReturn(const Function &F) {
+  // We can infer and propagate function attributes only when we know that the
+  // definition we'll get at link time is *exactly* the definition we see now.
+  // For more details, see GlobalValue::mayBeDerefined.
+  if (!F.hasExactDefinition())
+    return false;
+
   // Must-progress function without side-effects must return.
   if (F.mustProgress() && F.onlyReadsMemory())
     return true;


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