[llvm] 7c38ee2 - [FunctionAttrs][IR] Fix memory attr inference for volatile mem intrinsics (#122926)

[via llvm-commits]

Author: Nikita Popov
Date: 2025-06-25T09:29:37+02:00
New Revision: 7c38ee26d44124c93dc1553cde36837928c96d41

URL: https://github.com/llvm/llvm-project/commit/7c38ee26d44124c93dc1553cde36837928c96d41
DIFF: https://github.com/llvm/llvm-project/commit/7c38ee26d44124c93dc1553cde36837928c96d41.diff

LOG: [FunctionAttrs][IR] Fix memory attr inference for volatile mem intrinsics (#122926)

Per LangRef volatile operations can read and write inaccessible memory:

> any volatile operation can read and/or modify state which is not
> accessible via a regular load or store in this module

Model this by adding inaccessible memory effects in getMemoryEffects()
if the operation is volatile.

In the future, we should model volatile using operand bundles instead.

Fixes https://github.com/llvm/llvm-project/issues/120932.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/lib/IR/Instructions.cpp
    llvm/test/Transforms/FunctionAttrs/initializes.ll
    llvm/test/Transforms/FunctionAttrs/nosync.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 31611dfe4fd2f..86a2edbd8bd41 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -839,6 +839,10 @@ MemoryEffects BasicAAResult::getMemoryEffects(const CallBase *Call,
       FuncME |= MemoryEffects::readOnly();
     if (Call->hasClobberingOperandBundles())
       FuncME |= MemoryEffects::writeOnly();
+    if (Call->isVolatile()) {
+      // Volatile operations also access inaccessible memory.
+      FuncME |= MemoryEffects::inaccessibleMemOnly();
+    }
     Min &= FuncME;
   }
 

diff  --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 2d89ec1b0a8d3..8d9b545d4134f 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -643,6 +643,10 @@ MemoryEffects CallBase::getMemoryEffects() const {
       if (hasClobberingOperandBundles())
         FnME |= MemoryEffects::writeOnly();
     }
+    if (isVolatile()) {
+      // Volatile operations also access inaccessible memory.
+      FnME |= MemoryEffects::inaccessibleMemOnly();
+    }
     ME &= FnME;
   }
   return ME;

diff  --git a/llvm/test/Transforms/FunctionAttrs/initializes.ll b/llvm/test/Transforms/FunctionAttrs/initializes.ll
index 937595b5e9b74..5800bc1ca7864 100644
--- a/llvm/test/Transforms/FunctionAttrs/initializes.ll
+++ b/llvm/test/Transforms/FunctionAttrs/initializes.ll
@@ -443,7 +443,7 @@ define void @memset_neg(ptr %p) {
 }
 
 define void @memset_volatile(ptr %p) {
-; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: write)
+; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: write, inaccessiblemem: readwrite)
 ; CHECK-LABEL: define void @memset_volatile(
 ; CHECK-SAME: ptr writeonly [[P:%.*]]) #[[ATTR5:[0-9]+]] {
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr [[P]], i8 2, i64 9, i1 true)
@@ -478,7 +478,7 @@ define void @memcpy(ptr %p, ptr %p2) {
 }
 
 define void @memcpy_volatile(ptr %p, ptr %p2) {
-; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite)
+; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite, inaccessiblemem: readwrite)
 ; CHECK-LABEL: define void @memcpy_volatile(
 ; CHECK-SAME: ptr writeonly [[P:%.*]], ptr readonly [[P2:%.*]]) #[[ATTR6:[0-9]+]] {
 ; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr [[P]], ptr [[P2]], i64 9, i1 true)
@@ -541,7 +541,7 @@ define void @memmove(ptr %p, ptr %p2) {
 }
 
 define void @memmove_volatile(ptr %p, ptr %p2) {
-; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite)
+; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite, inaccessiblemem: readwrite)
 ; CHECK-LABEL: define void @memmove_volatile(
 ; CHECK-SAME: ptr writeonly [[P:%.*]], ptr readonly [[P2:%.*]]) #[[ATTR6]] {
 ; CHECK-NEXT:    call void @llvm.memmove.p0.p0.i64(ptr [[P]], ptr [[P2]], i64 9, i1 true)

diff  --git a/llvm/test/Transforms/FunctionAttrs/nosync.ll b/llvm/test/Transforms/FunctionAttrs/nosync.ll
index de5398f17ce51..9abfbb21a71a0 100644
--- a/llvm/test/Transforms/FunctionAttrs/nosync.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nosync.ll
@@ -236,7 +236,7 @@ declare void @llvm.memset(ptr %dest, i8 %val, i32 %len, i1 %isvolatile)
 
 ; negative, checking volatile intrinsics.
 define i32 @memcpy_volatile(ptr %ptr1, ptr %ptr2) {
-; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite)
+; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(argmem: readwrite, inaccessiblemem: readwrite)
 ; CHECK-LABEL: @memcpy_volatile(
 ; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i32(ptr [[PTR1:%.*]], ptr [[PTR2:%.*]], i32 8, i1 true)
 ; CHECK-NEXT:    ret i32 4