[MemProf] Look through alias when applying cloning in ThinLTO backend

[teresajohnson]

Mirror the handling in ModuleSummaryAnalysis to look through aliases
when handling call instructions in the ThinLTO backend MemProf handling.

Fixes #72094

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-lto

Author: Teresa Johnson (teresajohnson)

Changes

Mirror the handling in ModuleSummaryAnalysis to look through aliases
when handling call instructions in the ThinLTO backend MemProf handling.

Fixes #72094

---

Full diff: https://github.com/llvm/llvm-project/pull/72156.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp (+19-4)
• (added) llvm/test/ThinLTO/X86/memprof-distrib-alias.ll (+63)

diff --git a/llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp b/llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp
index e06c1552e14aa07..70a3f3067d9d6da 100644
--- a/llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp
+++ b/llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp
@@ -2984,6 +2984,21 @@ bool MemProfContextDisambiguation::applyImport(Module &M) {
         if (!mayHaveMemprofSummary(CB))
           continue;
 
+        auto *CalledValue = CB->getCalledOperand();
+        auto *CalledFunction = CB->getCalledFunction();
+        if (CalledValue && !CalledFunction) {
+          CalledValue = CalledValue->stripPointerCasts();
+          // Stripping pointer casts can reveal a called function.
+          CalledFunction = dyn_cast<Function>(CalledValue);
+        }
+        // Check if this is an alias to a function. If so, get the
+        // called aliasee for the checks below.
+        if (auto *GA = dyn_cast<GlobalAlias>(CalledValue)) {
+          assert(!CalledFunction &&
+                 "Expected null called function in callsite for alias");
+          CalledFunction = dyn_cast<Function>(GA->getAliaseeObject());
+        }
+
         CallStack<MDNode, MDNode::op_iterator> CallsiteContext(
             I.getMetadata(LLVMContext::MD_callsite));
         auto *MemProfMD = I.getMetadata(LLVMContext::MD_memprof);
@@ -3115,13 +3130,13 @@ bool MemProfContextDisambiguation::applyImport(Module &M) {
           CloneFuncIfNeeded(/*NumClones=*/StackNode.Clones.size());
 
           // Should have skipped indirect calls via mayHaveMemprofSummary.
-          assert(CB->getCalledFunction());
-          assert(!IsMemProfClone(*CB->getCalledFunction()));
+          assert(CalledFunction);
+          assert(!IsMemProfClone(*CalledFunction));
 
           // Update the calls per the summary info.
           // Save orig name since it gets updated in the first iteration
           // below.
-          auto CalleeOrigName = CB->getCalledFunction()->getName();
+          auto CalleeOrigName = CalledFunction->getName();
           for (unsigned J = 0; J < StackNode.Clones.size(); J++) {
             // Do nothing if this version calls the original version of its
             // callee.
@@ -3129,7 +3144,7 @@ bool MemProfContextDisambiguation::applyImport(Module &M) {
               continue;
             auto NewF = M.getOrInsertFunction(
                 getMemProfFuncName(CalleeOrigName, StackNode.Clones[J]),
-                CB->getCalledFunction()->getFunctionType());
+                CalledFunction->getFunctionType());
             CallBase *CBClone;
             // Copy 0 is the original function.
             if (!J)
diff --git a/llvm/test/ThinLTO/X86/memprof-distrib-alias.ll b/llvm/test/ThinLTO/X86/memprof-distrib-alias.ll
new file mode 100644
index 000000000000000..0059f10f48d45ff
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/memprof-distrib-alias.ll
@@ -0,0 +1,63 @@
+;; Test handling of memprof distributed ThinLTO when the call to update is an alias.
+
+;; Preparation steps to generate the bitcode and perform the thin link.
+; RUN: opt -thinlto-bc %s >%t.o
+; RUN: llvm-lto2 run %t.o -enable-memprof-context-disambiguation \
+; RUN:	-supports-hot-cold-new \
+; RUN:  -thinlto-distributed-indexes \
+; RUN:	-r=%t.o,main,plx \
+; RUN:	-r=%t.o,_Znam, \
+; RUN:	-o %t2.out
+
+;; Run ThinLTO backend
+; RUN: opt -passes=memprof-context-disambiguation \
+; RUN:	-memprof-import-summary=%t.o.thinlto.bc \
+; RUN:  -pass-remarks=memprof-context-disambiguation \
+; RUN:  %t.o -S 2>&1 | FileCheck %s --check-prefix=IR
+
+source_filename = "memprof-distrib-alias.ll"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @main() #0 {
+entry:
+  ;; The first call to fooAlias does not allocate cold memory. It should call
+  ;; the original function alias, which calls the original allocation decorated
+  ;; with a "notcold" attribute.
+  ; IR:   call {{.*}} @_Z8fooAliasv()
+  %call = call ptr @_Z8fooAliasv(), !callsite !0
+  ;; The second call to fooAlias allocates cold memory. It should call the
+  ;; cloned function which calls a cloned allocation decorated with a "cold"
+  ;; attribute.
+  ; IR:   call {{.*}} @_Z3foov.memprof.1()
+  %call1 = call ptr @_Z8fooAliasv(), !callsite !1
+  ret i32 0
+}
+
+; IR: define internal {{.*}} @_Z3foov()
+; IR:   call {{.*}} @_Znam(i64 0) #[[NOTCOLD:[0-9]+]]
+; IR: define internal {{.*}} @_Z3foov.memprof.1()
+; IR:   call {{.*}} @_Znam(i64 0) #[[COLD:[0-9]+]]
+; IR: attributes #[[NOTCOLD]] = { "memprof"="notcold" }
+; IR: attributes #[[COLD]] = { "memprof"="cold" }
+
+declare ptr @_Znam(i64)
+
+@_Z8fooAliasv = internal alias ptr (...), ptr @_Z3foov
+
+define internal ptr @_Z3foov() #0 {
+entry:
+  %call = call ptr @_Znam(i64 0), !memprof !2, !callsite !7
+  ret ptr null
+}
+
+attributes #0 = { noinline optnone }
+
+!0 = !{i64 8632435727821051414}
+!1 = !{i64 -3421689549917153178}
+!2 = !{!3, !5}
+!3 = !{!4, !"notcold"}
+!4 = !{i64 9086428284934609951, i64 8632435727821051414}
+!5 = !{!6, !"cold"}
+!6 = !{i64 9086428284934609951, i64 -3421689549917153178}
+!7 = !{i64 9086428284934609951}

[snehasish]

lgtm