[PATCH] D58694: LLVM: Optimization Pass: Function Attribute: Fix error caused by adding incompactible attribute to WriteOnly attribute of pointer argument

[Anh Tuyen Tran via Phabricator via llvm-commits]

anhtuyen updated this revision to Diff 193542.
anhtuyen retitled this revision from "LLVM: Optimization Pass: Function Attribute: nocapture should be added if the argument is WriteOnly" to "LLVM: Optimization Pass: Function Attribute: Fix error caused by adding incompactible attribute to WriteOnly attribute of pointer argument".
anhtuyen edited the summary of this revision.
anhtuyen added a comment.

Based on comments from the reviewers, if a pointer argument with attribute WriteOnly has no uses, there is no write through nor read from the pointer argument. In this case, its attribute can safely be strengthened from WriteOnly to ReadNone


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58694/new/

https://reviews.llvm.org/D58694

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


Index: llvm/test/Transforms/FunctionAttrs/writeonly.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/FunctionAttrs/writeonly.ll
@@ -0,0 +1,30 @@
+; RUN: opt < %s -functionattrs         -S | FileCheck %s
+; RUN: opt < %s -passes=function-attrs -S | FileCheck %s
+
+; CHECK: define void @nouses-argworn-funrn(i32* nocapture readnone %.aaa) #0 {
+define void @nouses-argworn-funrn(i32* writeonly %.aaa) {
+nouses-argworn-funrn_entry:
+  ret void
+}
+
+; CHECK: define void @nouses-argworn-funro(i32* nocapture readnone %.aaa, i32* nocapture readonly %.bbb) #1 {
+define void @nouses-argworn-funro(i32* writeonly %.aaa, i32* %.bbb) {
+nouses-argworn-funro_entry:
+  %val = load i32 , i32* %.bbb
+  ret void
+}
+
+%_type_of_d-ccc = type <{ i8*, i8, i8, i8, i8 }>
+
+ at d-ccc = internal global %_type_of_d-ccc <{ i8* null, i8 1, i8 13, i8 0, i8 -127 }>, align 8
+
+; CHECK: define void @nouses-argworn-funwo(i32* nocapture readnone %.aaa) #2 {
+define void @nouses-argworn-funwo(i32* writeonly %.aaa) {
+nouses-argworn-funwo_entry:
+  store i8 0, i8* getelementptr inbounds (%_type_of_d-ccc, %_type_of_d-ccc* @d-ccc, i32 0, i32 3)
+  ret void
+}
+
+; CHECK: attributes #0 = { norecurse nounwind readnone }
+; CHECK: attributes #1 = { norecurse nounwind readonly }
+; CHECK: attributes #2 = { norecurse nounwind writeonly }
Index: llvm/lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -720,9 +720,20 @@
         // Note that we don't allow any calls at all here, or else our result
         // will be dependent on the iteration order through the functions in the
         // SCC.
-        SmallPtrSet<Argument *, 8> Self;
-        Self.insert(&*A);
-        Attribute::AttrKind R = determinePointerReadAttrs(&*A, Self);
+
+        Attribute::AttrKind R = Attribute::ReadNone;
+        // Strengthen the attribute of a pointer argument A from WriteOnly
+        // to ReadNone when its uses is empty i.e. there is no actual
+        // write through nor read from the pointer argument A.
+        if (A->hasAttribute(Attribute::WriteOnly) &&
+            (A->materialized_use_empty())) {
+          A->removeAttr(Attribute::WriteOnly);
+        } else {
+          SmallPtrSet<Argument *, 8> Self;
+          Self.insert(&*A);
+          R = determinePointerReadAttrs(&*A, Self);
+        }
+
         if (R != Attribute::None) {
           A->addAttr(R);
           Changed = true;


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