[PATCH] D95862: [InlineFunction] Only update noalias scopes once for an instruction.

[Jeroen Dobbelaere via Phabricator via llvm-commits]

jeroen.dobbelaere created this revision.
jeroen.dobbelaere added reviewers: nikic, jdoerfert.
Herald added a subscriber: hiraditya.
jeroen.dobbelaere requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Inlining sometimes maps different instructions to be inlined onto the same instruction.

We must ensure to only remap the noalias scopes once. Otherwise the scope might disappear (at best). 
This patch ensures that we only replace scopes for which the mapping is known.

This approach is preferred over tracking which instructions we already handled in a SmallPtrSet,
as that one will need more memory.


https://reviews.llvm.org/D95862

Files:
  llvm/lib/Transforms/Utils/InlineFunction.cpp
  llvm/test/Transforms/Inline/noalias3.ll


Index: llvm/test/Transforms/Inline/noalias3.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/Inline/noalias3.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature
+; RUN: opt -inline -S < %s | FileCheck %s
+
+define void @caller(i8* %ptr) {
+; CHECK-LABEL: define {{[^@]+}}@caller
+; CHECK-SAME: (i8* [[PTR:%.*]]) {
+; CHECK-NEXT:    [[I_I:%.*]] = load i8, i8* [[PTR]], align 1, !alias.scope !0
+; CHECK-NEXT:    ret void
+;
+  call void @callee(i8* %ptr)
+  ret void
+}
+
+define void @callee(i8* %ptr) {
+; CHECK-LABEL: define {{[^@]+}}@callee
+; CHECK-SAME: (i8* [[PTR:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[I:%.*]] = load i8, i8* [[PTR]], align 1, !alias.scope !3
+; CHECK-NEXT:    br label [[DUMMY:%.*]]
+; CHECK:       dummy:
+; CHECK-NEXT:    [[I_COPY:%.*]] = phi i8 [ [[I]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret void
+;
+entry:
+  %i = load i8, i8* %ptr, !alias.scope !0
+  br label %dummy
+
+dummy:
+  %i.copy = phi i8 [ %i, %entry ]
+  ret void
+}
+
+!0 = !{!1}
+!1 = distinct !{!1, !2}
+!2 = distinct !{!2}
Index: llvm/lib/Transforms/Utils/InlineFunction.cpp
===================================================================
--- llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -921,14 +921,20 @@
     if (!I)
       continue;
 
+    // Only update scopes when we find them in the map. If they are not, it is
+    // because we already handled that instruction before. This is faster than
+    // tracking which instructions we already updated.
     if (MDNode *M = I->getMetadata(LLVMContext::MD_alias_scope))
-      I->setMetadata(LLVMContext::MD_alias_scope, MDMap[M]);
+      if (MDNode *MNew = MDMap.lookup(M))
+        I->setMetadata(LLVMContext::MD_alias_scope, MNew);
 
     if (MDNode *M = I->getMetadata(LLVMContext::MD_noalias))
-      I->setMetadata(LLVMContext::MD_noalias, MDMap[M]);
+      if (MDNode *MNew = MDMap.lookup(M))
+        I->setMetadata(LLVMContext::MD_noalias, MNew);
 
     if (auto *Decl = dyn_cast<NoAliasScopeDeclInst>(I))
-      Decl->setScopeList(MDMap[Decl->getScopeList()]);
+      if (MDNode *MNew = MDMap.lookup(Decl->getScopeList()))
+        Decl->setScopeList(MNew);
   }
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D95862.320738.patch
Type: text/x-patch
Size: 2327 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210202/b372e0c9/attachment.bin>