Extend global merge pass to optionally consider global constant variables.

Also add some checks to not merge globals used within landing pad instructions or marked as "used".


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177331 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 130 insertions, 6 deletions

diff --git a/lib/Transforms/Scalar/GlobalMerge.cpp b/lib/Transforms/Scalar/GlobalMerge.cpp
index 1601a8d646..14e463ad2d 100644
--- a/lib/Transforms/Scalar/GlobalMerge.cpp
+++ b/lib/Transforms/Scalar/GlobalMerge.cpp
@@ -53,6 +53,7 @@
 
 #define DEBUG_TYPE "global-merge"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/Constants.h"
@@ -60,14 +61,22 @@
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetLoweringObjectFile.h"
 using namespace llvm;
 
+static cl::opt<bool>
+EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
+                  	cl::desc("Enable global merge pass on constants"),
+                  	cl::init(false));
+
 STATISTIC(NumMerged      , "Number of globals merged");
 namespace {
   class GlobalMerge : public FunctionPass {
@@ -78,6 +87,23 @@ namespace {
     bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
                  Module &M, bool isConst, unsigned AddrSpace) const;
 
+    /// \brief Check if the given variable has been identified as must keep
+    /// \pre setMustKeepGlobalVariables must have been called on the Module that
+    ///      contains GV
+    bool isMustKeepGlobalVariable(const GlobalVariable *GV) const {
+      return MustKeepGlobalVariables.count(GV);
+    }
+
+    /// Collect every variables marked as "used" or used in a landing pad
+    /// instruction for this Module.
+    void setMustKeepGlobalVariables(Module &M);
+
+    /// Collect every variables marked as "used"
+    void collectUsedGlobalVariables(Module &M);
+
+    /// Keep track of the GlobalVariable that are marked as "used"
+    SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables;
+
   public:
     static char ID;             // Pass identification, replacement for typeid.
     explicit GlobalMerge(const TargetLowering *tli = 0)
@@ -169,6 +195,46 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
   return true;
 }
 
+void GlobalMerge::collectUsedGlobalVariables(Module &M) {
+  // Extract global variables from llvm.used array
+  const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
+  if (!GV || !GV->hasInitializer()) return;
+
+  // Should be an array of 'i8*'.
+  const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
+  if (InitList == 0) return;
+ 
+  for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
+    if (const GlobalVariable *G =
+        dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))
+      MustKeepGlobalVariables.insert(G);
+}
+
+void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
+  // If we already processed a Module, UsedGlobalVariables may have been
+  // populated. Reset the information for this module.
+  MustKeepGlobalVariables.clear();
+  collectUsedGlobalVariables(M);
+
+  for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
+       ++IFn) {
+    for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
+         IBB != IEndBB; ++IBB) {
+      // Follow the inwoke link to find the landing pad instruction
+      const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
+      if (!II) continue;
+
+      const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
+      // Look for globals in the clauses of the landing pad instruction
+      for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
+           Idx != NumClauses; ++Idx)
+        if (const GlobalVariable *GV =
+            dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
+                                     ->stripPointerCasts()))
+          MustKeepGlobalVariables.insert(GV);
+    }
+  }
+}
 
 bool GlobalMerge::doInitialization(Module &M) {
   DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
@@ -176,6 +242,7 @@ bool GlobalMerge::doInitialization(Module &M) {
   const DataLayout *TD = TLI->getDataLayout();
   unsigned MaxOffset = TLI->getMaximalGlobalOffset();
   bool Changed = false;
+  setMustKeepGlobalVariables(M);
 
   // Grab all non-const globals.
   for (Module::global_iterator I = M.global_begin(),
@@ -200,6 +267,12 @@ bool GlobalMerge::doInitialization(Module &M) {
         I->getName().startswith(".llvm."))
       continue;
 
+    // Ignore all "required" globals:
+    // - the ones used for EH
+    // - the ones marked with "used" attribute
+    if (isMustKeepGlobalVariable(I))
+      continue;
+
     if (TD->getTypeAllocSize(Ty) < MaxOffset) {
       if (TargetLoweringObjectFile::getKindForGlobal(I, TLI->getTargetMachine())
           .isBSSLocal())
@@ -221,11 +294,11 @@ bool GlobalMerge::doInitialization(Module &M) {
     if (I->second.size() > 1)
       Changed |= doMerge(I->second, M, false, I->first);
 
-  // FIXME: This currently breaks the EH processing due to way how the
-  // typeinfo detection works. We might want to detect the TIs and ignore
-  // them in the future.
-  // if (ConstGlobals.size() > 1)
-  //  Changed |= doMerge(ConstGlobals, M, true);
+  if (EnableGlobalMergeOnConst)
+    for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
+         I = ConstGlobals.begin(), E = ConstGlobals.end(); I != E; ++I)
+      if (I->second.size() > 1)
+        Changed |= doMerge(I->second, M, true, I->first);
 
   return Changed;
 }
diff --git a/test/CodeGen/ARM/global-merge.ll b/test/CodeGen/ARM/global-merge.ll
index 1732df3fa5..f88e927961 100644
--- a/test/CodeGen/ARM/global-merge.ll
+++ b/test/CodeGen/ARM/global-merge.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -mtriple=thumb-apple-darwin | FileCheck %s
+; RUN: llc < %s -mtriple=thumb-apple-darwin -global-merge-on-const=true | FileCheck %s
 ; Test the ARMGlobalMerge pass.  Use -march=thumb because it has a small
 ; value for the maximum offset (127).
 
@@ -6,6 +6,52 @@
 ; CHECK: g0:
 @g0 = internal global [32 x i32] [ i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 1, i32 2 ]
 
+; Global variables marked with "used" attribute must be kept
+; CHECK: g8
+@g8 = internal global i32 0
+@llvm.used = appending global [1 x i8*] [i8* bitcast (i32* @g8 to i8*)], section "llvm.metadata"
+
+; Global used in landing pad instruction must be kept
+; CHECK: ZTIi
+@_ZTIi = internal global i8* null
+
+define i32 @_Z9exceptioni(i32 %arg) {
+bb:
+  %tmp = invoke i32 @_Z14throwSomethingi(i32 %arg)
+          to label %bb9 unwind label %bb1
+
+bb1:                                              ; preds = %bb
+  %tmp2 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_sj0 to i8*)
+          catch i8* bitcast (i8** @_ZTIi to i8*)
+  %tmp3 = extractvalue { i8*, i32 } %tmp2, 1
+  %tmp4 = tail call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*))
+  %tmp5 = icmp eq i32 %tmp3, %tmp4
+  br i1 %tmp5, label %bb6, label %bb10
+
+bb6:                                              ; preds = %bb1
+  %tmp7 = extractvalue { i8*, i32 } %tmp2, 0
+  %tmp8 = tail call i8* @__cxa_begin_catch(i8* %tmp7)
+  tail call void @__cxa_end_catch()
+  br label %bb9
+
+bb9:                                              ; preds = %bb6, %bb
+  %res.0 = phi i32 [ 0, %bb6 ], [ %tmp, %bb ]
+  ret i32 %res.0
+
+bb10:                                             ; preds = %bb1
+  resume { i8*, i32 } %tmp2
+}
+
+declare i32 @_Z14throwSomethingi(i32)
+
+declare i32 @__gxx_personality_sj0(...)
+
+declare i32 @llvm.eh.typeid.for(i8*)
+
+declare i8* @__cxa_begin_catch(i8*)
+
+declare void @__cxa_end_catch()
+
 ; CHECK: _MergedGlobals:
 @g1 = internal global i32 1
 @g2 = internal global i32 2
@@ -21,3 +67,8 @@
 ; CHECK: _MergedGlobals2
 @g4 = internal global i32 0
 @g5 = internal global i32 0
+
+; Global variables that are constant can be merged together
+; CHECK: _MergedGlobals3
+@g6 = internal constant [12 x i32] zeroinitializer, align 4
+@g7 = internal constant [12 x i32] zeroinitializer, align 4