[ARM] Promote small global constants to constant pools

If a constant is unamed_addr and is only used within one function, we can save
on the code size and runtime cost of an indirection by changing the global's storage
to inside the constant pool. For example, instead of:

      ldr r0, .CPI0
      bl printf
      bx lr
    .CPI0: &format_string
    format_string: .asciz "hello, world!\n"

We can emit:

      adr r0, .CPI0
      bl printf
      bx lr
    .CPI0: .asciz "hello, world!\n"

This can cause significant code size savings when many small strings are used in one
function (4 bytes per string).

This recommit contains fixes for a nasty bug related to fast-isel fallback - because
fast-isel doesn't know about this optimization, if it runs and emits references to
a string that we inline (because fast-isel fell back to SDAG) we will end up
with an inlined string and also an out-of-line string, and we won't emit the
out-of-line string, causing backend failures.

It also contains fixes for emitting .text relocations which made the sanitizer
bots unhappy.

llvm-svn: 282387

1 files changed, 10 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 90ca5206c74..f6da4b15ccf 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -898,13 +898,20 @@ MachineConstantPoolEntry::getSectionKind(const DataLayout *DL) const {
 }
 
 MachineConstantPool::~MachineConstantPool() {
+  // A constant may be a member of both Constants and MachineCPVsSharingEntries,
+  // so keep track of which we've deleted to avoid double deletions.
+  DenseSet<MachineConstantPoolValue*> Deleted;
   for (unsigned i = 0, e = Constants.size(); i != e; ++i)
-    if (Constants[i].isMachineConstantPoolEntry())
+    if (Constants[i].isMachineConstantPoolEntry()) {
+      Deleted.insert(Constants[i].Val.MachineCPVal);
       delete Constants[i].Val.MachineCPVal;
+    }
   for (DenseSet<MachineConstantPoolValue*>::iterator I =
        MachineCPVsSharingEntries.begin(), E = MachineCPVsSharingEntries.end();
-       I != E; ++I)
-    delete *I;
+       I != E; ++I) {
+    if (Deleted.count(*I) == 0)
+      delete *I;
+  }
 }
 
 /// Test whether the given two constants can be allocated the same constant pool