ARM: track globals promoted to coalesced const pool entries

Globals that are promoted to an ARM constant pool may alias with another
existing constant pool entry. We need to keep a reference to all globals
that were promoted to each constant pool value so that we can emit a
distinct label for each promoted global. These labels are necessary so
that debug info can refer to the promoted global without an undefined
reference during linking.

Patch by Stephen Crane!

llvm-svn: 312692

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

@@ -865,11 +865,12 @@ EmitMachineConstantPoolValue(MachineConstantPoolValue *MCPV) {
     // However, if this global is promoted into several functions we must ensure
     // we don't try and emit duplicate symbols!
     auto *ACPC = cast<ARMConstantPoolConstant>(ACPV);
-    auto *GV = ACPC->getPromotedGlobal();
+    for (const auto *GV : ACPC->promotedGlobals()) {
-    if (!EmittedPromotedGlobalLabels.count(GV)) {
+      if (!EmittedPromotedGlobalLabels.count(GV)) {
-      MCSymbol *GVSym = getSymbol(GV);
+        MCSymbol *GVSym = getSymbol(GV);
-      OutStreamer->EmitLabel(GVSym);
+        OutStreamer->EmitLabel(GVSym);
-      EmittedPromotedGlobalLabels.insert(GV);
+        EmittedPromotedGlobalLabels.insert(GV);
+      }
     }
     return EmitGlobalConstant(DL, ACPC->getPromotedGlobalInit());
   }

llvm/lib/Target/ARM/ARMConstantPoolValue.cpp

@@ -140,8 +140,9 @@ ARMConstantPoolConstant::ARMConstantPoolConstant(const Constant *C,
 ARMConstantPoolConstant::ARMConstantPoolConstant(const GlobalVariable *GV,
                                                  const Constant *C)
     : ARMConstantPoolValue((Type *)C->getType(), 0, ARMCP::CPPromotedGlobal, 0,
-                           ARMCP::no_modifier, false),
+                           ARMCP::no_modifier, false), CVal(C) {
-      CVal(C), GVar(GV) {}
+  GVars.insert(GV);
+}
 
 ARMConstantPoolConstant *
 ARMConstantPoolConstant::Create(const Constant *C, unsigned ID) {
@@ -189,7 +190,15 @@ const BlockAddress *ARMConstantPoolConstant::getBlockAddress() const {
 
 int ARMConstantPoolConstant::getExistingMachineCPValue(MachineConstantPool *CP,
                                                        unsigned Alignment) {
-  return getExistingMachineCPValueImpl<ARMConstantPoolConstant>(CP, Alignment);
+  int index =
+    getExistingMachineCPValueImpl<ARMConstantPoolConstant>(CP, Alignment);
+  if (index != -1) {
+    auto *CPV = static_cast<ARMConstantPoolValue*>(
+        CP->getConstants()[index].Val.MachineCPVal);
+    auto *Constant = cast<ARMConstantPoolConstant>(CPV);
+    Constant->GVars.insert(GVars.begin(), GVars.end());
+  }
+  return index;
 }
 
 bool ARMConstantPoolConstant::hasSameValue(ARMConstantPoolValue *ACPV) {
@@ -199,6 +208,8 @@ bool ARMConstantPoolConstant::hasSameValue(ARMConstantPoolValue *ACPV) {
 
 void ARMConstantPoolConstant::addSelectionDAGCSEId(FoldingSetNodeID &ID) {
   ID.AddPointer(CVal);
+  for (const auto *GV : GVars)
+    ID.AddPointer(GV);
   ARMConstantPoolValue::addSelectionDAGCSEId(ID);
 }
 

llvm/lib/Target/ARM/ARMConstantPoolValue.h

@@ -15,6 +15,7 @@
 #define LLVM_LIB_TARGET_ARM_ARMCONSTANTPOOLVALUE_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/Support/Casting.h"
 #include <string>
@@ -80,8 +81,8 @@ protected:
     for (unsigned i = 0, e = Constants.size(); i != e; ++i) {
       if (Constants[i].isMachineConstantPoolEntry() &&
           (Constants[i].getAlignment() & AlignMask) == 0) {
-        ARMConstantPoolValue *CPV =
+        auto *CPV =
-            (ARMConstantPoolValue *)Constants[i].Val.MachineCPVal;
+          static_cast<ARMConstantPoolValue*>(Constants[i].Val.MachineCPVal);
         if (Derived *APC = dyn_cast<Derived>(CPV))
           if (cast<Derived>(this)->equals(APC))
             return i;
@@ -139,7 +140,7 @@ inline raw_ostream &operator<<(raw_ostream &O, const ARMConstantPoolValue &V) {
 /// Functions, and BlockAddresses.
 class ARMConstantPoolConstant : public ARMConstantPoolValue {
   const Constant *CVal;         // Constant being loaded.
-  const GlobalVariable *GVar = nullptr;
+  SmallPtrSet<const GlobalVariable*, 1> GVars;
 
   ARMConstantPoolConstant(const Constant *C,
                           unsigned ID,
@@ -173,8 +174,9 @@ public:
   const GlobalValue *getGV() const;
   const BlockAddress *getBlockAddress() const;
 
-  const GlobalVariable *getPromotedGlobal() const {
+  typedef SmallPtrSet<const GlobalVariable *, 1>::iterator promoted_iterator;
-    return dyn_cast_or_null<GlobalVariable>(GVar);
+  iterator_range<promoted_iterator> promotedGlobals() {
+    return iterator_range<promoted_iterator>(GVars.begin(), GVars.end());
   }
 
   const Constant *getPromotedGlobalInit() const {

llvm/test/CodeGen/ARM/constantpool-promote-duplicate.ll

@@ -0,0 +1,21 @@
+; RUN: llc -mtriple=arm-eabi -relocation-model=static -arm-promote-constant < %s | FileCheck %s
+
+@const1 = private unnamed_addr constant i32 0, align 4
+@const2 = private unnamed_addr constant i32 0, align 4
+
+; const1 and const2 both need labels for debug info, but will be coalesced into
+; a single constpool entry
+
+; CHECK-LABEL: @test1
+; CHECK-DAG: const1:
+; CHECK-DAG: const2:
+; CHECK: .fnend
+define void @test1() {
+  %1 = load i32, i32* @const1, align 4
+  call void @a(i32 %1)
+  %2 = load i32, i32* @const2, align 4
+  call void @a(i32 %2)
+  ret void
+}
+
+declare void @a(i32)