Re-apply r286006: Fix 24560: assembler does not share constant pool for same constants

Re-applying now that the open bug on this commit, PR32825, is known to be fixed.

Original commit message:
    Summary: This patch returns the same label if the CP entry with the same value has been created.

    Reviewers: eli.friedman, rengolin, jmolloy

    Subscribers: majnemer, jmolloy, llvm-commits

    Differential Revision: https://reviews.llvm.org/D25804

llvm-svn: 303539

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/MC/ConstantPools.cpp b/llvm/lib/MC/ConstantPools.cpp
index 1763d099115..8c94e278099 100644
--- a/llvm/lib/MC/ConstantPools.cpp
+++ b/llvm/lib/MC/ConstantPools.cpp
@@ -39,10 +39,20 @@ void ConstantPool::emitEntries(MCStreamer &Streamer) {
 
 const MCExpr *ConstantPool::addEntry(const MCExpr *Value, MCContext &Context,
                                      unsigned Size, SMLoc Loc) {
+  const MCConstantExpr *C = dyn_cast<MCConstantExpr>(Value);
+
+  // Check if there is existing entry for the same constant. If so, reuse it.
+  auto Itr = C ? CachedEntries.find(C->getValue()) : CachedEntries.end();
+  if (Itr != CachedEntries.end())
+    return Itr->second;
+
   MCSymbol *CPEntryLabel = Context.createTempSymbol();
 
   Entries.push_back(ConstantPoolEntry(CPEntryLabel, Value, Size, Loc));
-  return MCSymbolRefExpr::create(CPEntryLabel, Context);
+  const auto SymRef = MCSymbolRefExpr::create(CPEntryLabel, Context);
+  if (C)
+    CachedEntries[C->getValue()] = SymRef;
+  return SymRef;
 }
 
 bool ConstantPool::empty() { return Entries.empty(); }