From e508dd4c75705f325764e1197854c0e83266a7ea Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 3 Jan 2011 23:38:13 +0000
Subject: [PATCH] Duncan deftly points out that readnone functions aren't
 invalidated by stores, so they can be handled as 'simple' operations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122785 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/EarlyCSE.cpp |  6 +++++-
 test/Transforms/EarlyCSE/basic.ll  | 13 +++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Scalar/EarlyCSE.cpp b/lib/Transforms/Scalar/EarlyCSE.cpp
index 6c2ea39896a..3d3f17b26fc 100644
--- a/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -56,6 +56,9 @@ namespace {
     }
     
     static bool canHandle(Instruction *Inst) {
+      // This can only handle non-void readnone functions.
+      if (CallInst *CI = dyn_cast<CallInst>(Inst))
+        return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
       return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
              isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
              isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
@@ -105,7 +108,8 @@ unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
       Res ^= *I;
   } else {
     // nothing extra to hash in.
-    assert((isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
+    assert((isa<CallInst>(Inst) ||
+            isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
             isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
             isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
            "Invalid/unknown instruction");
diff --git a/test/Transforms/EarlyCSE/basic.ll b/test/Transforms/EarlyCSE/basic.ll
index bc152e70624..e3c75f97dcf 100644
--- a/test/Transforms/EarlyCSE/basic.ll
+++ b/test/Transforms/EarlyCSE/basic.ll
@@ -106,3 +106,16 @@ define void @test7(i32 *%P) {
   ; CHECK-NEXT: store i32 45
   ; CHECK-NEXT: ret void
 }
+
+;; Readnone functions aren't invalidated by stores.
+; CHECK: @test8
+define i32 @test8(i32 *%P) {
+  %V1 = call i32 @func(i32* %P) readnone
+  store i32 4, i32* %P
+  %V2 = call i32 @func(i32* %P) readnone
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: ret i32 0
+}
+
+
-- 
2.34.1