[llvm] [MemoryLocation][DSE] Allow other read effects in MemoryLocation::getForDest() (PR #144343)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

MemoryLocation::getForDest() returns a (potentially) written location, while still allowing other reads. Currently, this is limited to argmemonly functions. However, we can ignore other (non-argmem) read effects here for the same reason we can ignore argument reads.
    
Fixes https://github.com/llvm/llvm-project/issues/144300.


---
Full diff: https://github.com/llvm/llvm-project/pull/144343.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/MemoryLocation.cpp (+3-1) 
- (modified) llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll (+21) 


``````````diff
diff --git a/llvm/lib/Analysis/MemoryLocation.cpp b/llvm/lib/Analysis/MemoryLocation.cpp
index 3b42bb412b9ba..c8daab7abde18 100644
--- a/llvm/lib/Analysis/MemoryLocation.cpp
+++ b/llvm/lib/Analysis/MemoryLocation.cpp
@@ -111,7 +111,9 @@ MemoryLocation MemoryLocation::getForDest(const AnyMemIntrinsic *MI) {
 
 std::optional<MemoryLocation>
 MemoryLocation::getForDest(const CallBase *CB, const TargetLibraryInfo &TLI) {
-  if (!CB->onlyAccessesArgMemory())
+  // Check that the only possible writes are to arguments.
+  MemoryEffects WriteME = CB->getMemoryEffects() & MemoryEffects::writeOnly();
+  if (!WriteME.onlyAccessesArgPointees())
     return std::nullopt;
 
   if (CB->hasOperandBundles())
diff --git a/llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll b/llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
index 030d315bfd925..8a69f1f55d491 100644
--- a/llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
@@ -286,3 +286,24 @@ define void @test_dse_non_alloca() {
   ret void
 }
 
+define void @test_other_read_effects() {
+; CHECK-LABEL: @test_other_read_effects(
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  call void @f(ptr %a) memory(read, argmem: readwrite) nounwind willreturn
+  ret void
+}
+
+define i32 @test_other_read_effects_read_after() {
+; CHECK-LABEL: @test_other_read_effects_read_after(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    call void @f(ptr [[A]]) #[[ATTR5:[0-9]+]]
+; CHECK-NEXT:    [[V:%.*]] = load i32, ptr [[A]], align 4
+; CHECK-NEXT:    ret i32 [[V]]
+;
+  %a = alloca i32, align 4
+  call void @f(ptr %a) memory(read, argmem: readwrite) nounwind willreturn
+  %v = load i32, ptr %a
+  ret i32 %v
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/144343