[ARM] Prefer indirect calls in minsize mode

... When we emit several calls to the same function in the same basic block.

An indirect call uses a "BLX r0" instruction which has a 16-bit encoding. If many calls are made to the same target, this can enable significant code size reductions.

llvm-svn: 275537

1 files changed, 42 insertions, 28 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index b902b6056fc..1542934aa77 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -1849,36 +1849,50 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
           false, false, 0);
     }
   } else if (isa<GlobalAddressSDNode>(Callee)) {
-    isDirect = true;
-    bool isDef = GV->isStrongDefinitionForLinker();
-
-    // ARM call to a local ARM function is predicable.
-    isLocalARMFunc = !Subtarget->isThumb() && (isDef || !ARMInterworking);
-    // tBX takes a register source operand.
-    if (isStub && Subtarget->isThumb1Only() && !Subtarget->hasV5TOps()) {
-      assert(Subtarget->isTargetMachO() && "WrapperPIC use on non-MachO?");
-      Callee = DAG.getNode(
-          ARMISD::WrapperPIC, dl, PtrVt,
-          DAG.getTargetGlobalAddress(GV, dl, PtrVt, 0, ARMII::MO_NONLAZY));
-      Callee = DAG.getLoad(PtrVt, dl, DAG.getEntryNode(), Callee,
-                           MachinePointerInfo::getGOT(DAG.getMachineFunction()),
-                           false, false, true, 0);
-    } else if (Subtarget->isTargetCOFF()) {
-      assert(Subtarget->isTargetWindows() &&
-             "Windows is the only supported COFF target");
-      unsigned TargetFlags = GV->hasDLLImportStorageClass()
-                                 ? ARMII::MO_DLLIMPORT
-                                 : ARMII::MO_NO_FLAG;
-      Callee =
-          DAG.getTargetGlobalAddress(GV, dl, PtrVt, /*Offset=*/0, TargetFlags);
-      if (GV->hasDLLImportStorageClass())
+    // If we're optimizing for minimum size and the function is called many
+    // times in this block, we can improve codesize by calling indirectly
+    // as BLXr has a 16-bit encoding.
+    auto *GV = cast<GlobalAddressSDNode>(Callee)->getGlobal();
+    auto *BB = CLI.CS->getParent();
+    bool PreferIndirect =
+        Subtarget->isThumb() && MF.getFunction()->optForMinSize() &&
+        std::count_if(GV->user_begin(), GV->user_end(), [&BB](const User *U) {
+          return isa<Instruction>(U) && cast<Instruction>(U)->getParent() == BB;
+        }) > 2;
+
+    if (!PreferIndirect) {
+      isDirect = true;
+      bool isDef = GV->isStrongDefinitionForLinker();
+
+      // ARM call to a local ARM function is predicable.
+      isLocalARMFunc = !Subtarget->isThumb() && (isDef || !ARMInterworking);
+      // tBX takes a register source operand.
+      if (isStub && Subtarget->isThumb1Only() && !Subtarget->hasV5TOps()) {
+        assert(Subtarget->isTargetMachO() && "WrapperPIC use on non-MachO?");
+        Callee = DAG.getNode(
+            ARMISD::WrapperPIC, dl, PtrVt,
+            DAG.getTargetGlobalAddress(GV, dl, PtrVt, 0, ARMII::MO_NONLAZY));
         Callee =
-            DAG.getLoad(PtrVt, dl, DAG.getEntryNode(),
-                        DAG.getNode(ARMISD::Wrapper, dl, PtrVt, Callee),
+            DAG.getLoad(PtrVt, dl, DAG.getEntryNode(), Callee,
                         MachinePointerInfo::getGOT(DAG.getMachineFunction()),
-                        false, false, false, 0);
-    } else {
-      Callee = DAG.getTargetGlobalAddress(GV, dl, PtrVt, 0, 0);
+                        false, false, true, 0);
+      } else if (Subtarget->isTargetCOFF()) {
+        assert(Subtarget->isTargetWindows() &&
+               "Windows is the only supported COFF target");
+        unsigned TargetFlags = GV->hasDLLImportStorageClass()
+                                   ? ARMII::MO_DLLIMPORT
+                                   : ARMII::MO_NO_FLAG;
+        Callee = DAG.getTargetGlobalAddress(GV, dl, PtrVt, /*Offset=*/0,
+                                            TargetFlags);
+        if (GV->hasDLLImportStorageClass())
+          Callee =
+              DAG.getLoad(PtrVt, dl, DAG.getEntryNode(),
+                          DAG.getNode(ARMISD::Wrapper, dl, PtrVt, Callee),
+                          MachinePointerInfo::getGOT(DAG.getMachineFunction()),
+                          false, false, false, 0);
+      } else {
+        Callee = DAG.getTargetGlobalAddress(GV, dl, PtrVt, 0, 0);
+      }
     }
   } else if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee)) {
     isDirect = true;