From 241f65321efc6ad84ed875cd9494df8ca1cff309 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Thu, 17 Apr 2008 05:36:50 +0000
Subject: [PATCH] Make GVN able to remove unnecessary calls to read-only
 functions again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49842 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/MemoryDependenceAnalysis.cpp     |  3 +-
 lib/Transforms/Scalar/GVN.cpp                 | 46 ++++++++++++-------
 .../{const-dce.ll => pure-const-dce.ll}       |  2 +-
 3 files changed, 32 insertions(+), 19 deletions(-)
 rename test/Analysis/BasicAA/{const-dce.ll => pure-const-dce.ll} (99%)

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 314d6e4b3a7..161c2fed1c7 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -134,8 +134,7 @@ Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C,
     } else if (isa<CallInst>(QI)) {
       AliasAnalysis::ModRefBehavior result =
                    AA.getModRefBehavior(CallSite::get(QI));
-      if (result != AliasAnalysis::DoesNotAccessMemory &&
-          result != AliasAnalysis::OnlyReadsMemory) {
+      if (result != AliasAnalysis::DoesNotAccessMemory) {
         if (!start && !block) {
           cachedResult.first = QI;
           cachedResult.second = true;
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index b33d3af31fc..bd360520a70 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -135,6 +135,7 @@ namespace {
       DenseMap<Value*, uint32_t> valueNumbering;
       DenseMap<Expression, uint32_t> expressionNumbering;
       AliasAnalysis* AA;
+      MemoryDependenceAnalysis* MD;
   
       uint32_t nextValueNumber;
     
@@ -159,6 +160,7 @@ namespace {
       void erase(Value* v);
       unsigned size();
       void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
+      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
   };
 }
 
@@ -432,6 +434,33 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
       
         return nextValueNumber++;
       }
+    } else if (AA->onlyReadsMemory(C)) {
+      Expression e = create_expression(C);
+      
+      Instruction* dep = MD->getDependency(C);
+      
+      if (dep == MemoryDependenceAnalysis::NonLocal ||
+          !isa<CallInst>(dep)) {
+        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+        return nextValueNumber++;
+      }
+      
+      CallInst* cdep = cast<CallInst>(dep);
+      Expression d_exp = create_expression(cdep);
+      
+      if (e != d_exp) {
+        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+        return nextValueNumber++;
+      } else {
+        uint32_t v = expressionNumbering[d_exp];
+        valueNumbering.insert(std::make_pair(V, v));
+        return v;
+      }
+      
     } else {
       valueNumbering.insert(std::make_pair(V, nextValueNumber));
       return nextValueNumber++;
@@ -993,22 +1022,6 @@ bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
   } else if (currAvail.test(num)) {
     Value* repl = find_leader(currAvail, num);
     
-    if (CallInst* CI = dyn_cast<CallInst>(I)) {
-      AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
-      if (!AA.doesNotAccessMemory(CI)) {
-        MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-        if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
-            MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
-          // There must be an intervening may-alias store, so nothing from
-          // this point on will be able to be replaced with the preceding call
-          currAvail.erase(repl);
-          currAvail.insert(I);
-          
-          return false;
-        }
-      }
-    }
-    
     // Remove it!
     MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
     MD.removeInstruction(I);
@@ -1030,6 +1043,7 @@ bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
 //
 bool GVN::runOnFunction(Function& F) {
   VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
+  VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
   
   bool changed = false;
   bool shouldContinue = true;
diff --git a/test/Analysis/BasicAA/const-dce.ll b/test/Analysis/BasicAA/pure-const-dce.ll
similarity index 99%
rename from test/Analysis/BasicAA/const-dce.ll
rename to test/Analysis/BasicAA/pure-const-dce.ll
index dcde91434ff..b01b5c5cb81 100644
--- a/test/Analysis/BasicAA/const-dce.ll
+++ b/test/Analysis/BasicAA/pure-const-dce.ll
@@ -1,5 +1,5 @@
 ; RUN: llvm-as < %s | opt -basicaa -gvn | llvm-dis | grep TestConst | count 2
-; RUN: llvm-as < %s | opt -basicaa -gvn | llvm-dis | grep TestPure  | count 4
+; RUN: llvm-as < %s | opt -basicaa -gvn | llvm-dis | grep TestPure  | count 3
 ; RUN: llvm-as < %s | opt -basicaa -gvn | llvm-dis | grep TestNone  | count 4
 @g = global i32 0		; <i32*> [#uses=1]
 
-- 
2.34.1