[llvm] c23e1cb - [BasicAA] Treat ExtractValue(Argument) similar to Argument in relation to function-local objects. (#134716)

[via llvm-commits]

Author: David Green
Date: 2025-04-08T10:05:58+01:00
New Revision: c23e1cb9362067d3565a78590db8c5e68b74cf17

URL: https://github.com/llvm/llvm-project/commit/c23e1cb9362067d3565a78590db8c5e68b74cf17
DIFF: https://github.com/llvm/llvm-project/commit/c23e1cb9362067d3565a78590db8c5e68b74cf17.diff

LOG: [BasicAA] Treat ExtractValue(Argument) similar to Argument in relation to function-local objects. (#134716)

This is a much smaller, technically orthogonal patch similar to #134505. It
states that a extractvalue(Argument) can be treated like an Argument for alias
analysis, where the extractelement acts like a phi / copy. No inttoptr here.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/test/Analysis/BasicAA/noalias-inttoptr.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 4d1a95a0c4b43..12d9c8706a8e1 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1533,6 +1533,16 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
   return Alias;
 }
 
+// Return true for an Argument or extractvalue(Argument). These are all known
+// to not alias with FunctionLocal objects and can come up from coerced function
+// arguments.
+static bool isArgumentOrArgumentLike(const Value *V) {
+  if (isa<Argument>(V))
+    return true;
+  auto *E = dyn_cast<ExtractValueInst>(V);
+  return E && isa<Argument>(E->getOperand(0));
+}
+
 /// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as
 /// array references.
 AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
@@ -1585,8 +1595,8 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
 
     // Function arguments can't alias with things that are known to be
     // unambigously identified at the function level.
-    if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
-        (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
+    if ((isArgumentOrArgumentLike(O1) && isIdentifiedFunctionLocal(O2)) ||
+        (isArgumentOrArgumentLike(O2) && isIdentifiedFunctionLocal(O1)))
       return AliasResult::NoAlias;
 
     // If one pointer is the result of a call/invoke or load and the other is a

diff  --git a/llvm/test/Analysis/BasicAA/noalias-inttoptr.ll b/llvm/test/Analysis/BasicAA/noalias-inttoptr.ll
index 72f9adc5a74bf..cdfdb091f668f 100644
--- a/llvm/test/Analysis/BasicAA/noalias-inttoptr.ll
+++ b/llvm/test/Analysis/BasicAA/noalias-inttoptr.ll
@@ -73,7 +73,7 @@ define void @test_extractvalue([2 x ptr] %Q.coerce) {
 ; Same as test_extractvalue with an escape of %P
 define void @test_extractvalue_escape([2 x ptr] %Q.coerce) {
   ; CHECK-LABEL: Function: test_extractvalue_escape:
-  ; CHECK: MayAlias:    i8* %P, i8* %Q
+  ; CHECK: NoAlias:    i8* %P, i8* %Q
   %P = alloca i8
   call void @escape(ptr %P)
   %Q = extractvalue [2 x ptr] %Q.coerce, 1