[EarlyCSE] Don't DSE across readnone functions that may throw

Summary: Depends on D28740

Reviewers: dberlin, chandlerc, hfinkel, majnemer

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D28741

llvm-svn: 292249

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

@@ -761,12 +761,13 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
       continue;
     }
 
-    // If this instruction may read from memory, forget LastStore.
-    // Load/store intrinsics will indicate both a read and a write to
-    // memory.  The target may override this (e.g. so that a store intrinsic
-    // does not read  from memory, and thus will be treated the same as a
-    // regular store for commoning purposes).
-    if (Inst->mayReadFromMemory() &&
+    // If this instruction may read from memory or throw (and potentially read
+    // from memory in the exception handler), forget LastStore.  Load/store
+    // intrinsics will indicate both a read and a write to memory.  The target
+    // may override this (e.g. so that a store intrinsic does not read from
+    // memory, and thus will be treated the same as a regular store for
+    // commoning purposes).
+    if ((Inst->mayReadFromMemory() || Inst->mayThrow()) &&
         !(MemInst.isValid() && !MemInst.mayReadFromMemory()))
       LastStore = nullptr;
 

llvm/test/Transforms/EarlyCSE/readnone-mayunwind.ll

@@ -0,0 +1,15 @@
+; RUN: opt -S -early-cse < %s | FileCheck %s
+
+declare void @readnone_may_unwind() readnone
+
+define void @f(i32* %ptr) {
+; CHECK-LABEL: @f(
+; CHECK: store i32 100, i32* %ptr
+; CHECK: call void @readnone_may_unwind()
+; CHECK: store i32 200, i32* %ptr
+
+  store i32 100, i32* %ptr
+  call void @readnone_may_unwind()
+  store i32 200, i32* %ptr
+  ret void
+}