[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 #120932.

Author: nikic

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;
   }
 

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;

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)

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