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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

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.

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

---
Full diff: https://github.com/llvm/llvm-project/pull/122926.diff


4 Files Affected:

- (modified) llvm/lib/Analysis/BasicAliasAnalysis.cpp (+4) 
- (modified) llvm/lib/IR/Instructions.cpp (+4) 
- (modified) llvm/test/Transforms/FunctionAttrs/initializes.ll (+3-3) 
- (modified) llvm/test/Transforms/FunctionAttrs/nosync.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b2a3f3390e000d..2bed294c607768 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -824,6 +824,10 @@ 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 b8b2c1d7f9a859..3c69d82dfda073 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -615,6 +615,10 @@ 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 62f217aa3f7de9..b2e6c284747eb7 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 de5398f17ce51d..9abfbb21a71a0a 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

``````````

</details>


https://github.com/llvm/llvm-project/pull/122926