[PATCH] D28741: [EarlyCSE] Don't DSE across readnone functions that may throw

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy created this revision.
sanjoy added reviewers: dberlin, chandlerc, hfinkel.
sanjoy added a subscriber: llvm-commits.
sanjoy added a dependency: D28740: [LangRef] Explicitly allow readnone and reaodnly functions to unwind.
Herald added a subscriber: mcrosier.

Depends on https://reviews.llvm.org/D28740


https://reviews.llvm.org/D28741

Files:
  include/llvm/IR/Instruction.h
  lib/Transforms/Scalar/EarlyCSE.cpp
  test/Transforms/EarlyCSE/readnone-mayunwind.ll


Index: test/Transforms/EarlyCSE/readnone-mayunwind.ll
===================================================================
--- /dev/null
+++ 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
+}
Index: lib/Transforms/Scalar/EarlyCSE.cpp
===================================================================
--- lib/Transforms/Scalar/EarlyCSE.cpp
+++ lib/Transforms/Scalar/EarlyCSE.cpp
@@ -766,7 +766,7 @@
     // 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 (Inst->mayReadFromMemoryOrThrow() &&
         !(MemInst.isValid() && !MemInst.mayReadFromMemory()))
       LastStore = nullptr;
 
Index: include/llvm/IR/Instruction.h
===================================================================
--- include/llvm/IR/Instruction.h
+++ include/llvm/IR/Instruction.h
@@ -424,6 +424,11 @@
   /// Return true if this instruction may throw an exception.
   bool mayThrow() const;
 
+  /// Return true if this instruction may throw an exception or read memory.
+  bool mayReadFromMemoryOrThrow() const {
+    return mayReadFromMemory() || mayThrow();
+  }
+
   /// Return true if this instruction behaves like a memory fence: it can load
   /// or store to memory location without being given a memory location.
   bool isFenceLike() const {


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