[llvm] 62cdcd6 - [FuncAttrs] Don't infer willreturn for nonexact definitions

[via llvm-commits]

Author: sstefan1
Date: 2021-04-21T21:26:09+02:00
New Revision: 62cdcd6c5aee89e2cbdc498e5a6193d19bd498fb

URL: https://github.com/llvm/llvm-project/commit/62cdcd6c5aee89e2cbdc498e5a6193d19bd498fb
DIFF: https://github.com/llvm/llvm-project/commit/62cdcd6c5aee89e2cbdc498e5a6193d19bd498fb.diff

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

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

Differential Revision: https://reviews.llvm.org/D100988

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index 8f80a61ae08ee..ca8660a98ded8 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1432,6 +1432,12 @@ static bool addNoReturnAttrs(const SCCNodeSet &SCCNodes) {
 }
 
 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;

diff  --git a/llvm/test/Transforms/FunctionAttrs/willreturn.ll b/llvm/test/Transforms/FunctionAttrs/willreturn.ll
index 1f69c3d80d8b7..35f48e7a344c0 100644
--- a/llvm/test/Transforms/FunctionAttrs/willreturn.ll
+++ b/llvm/test/Transforms/FunctionAttrs/willreturn.ll
@@ -153,5 +153,12 @@ bb2:
   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