[PATCH] Use movw/movt instead of constant pool loads to lower byval parameter copies

[Derek Schuff]

Hi jfb,

The ARM backend can use a loop to implement copying byval parameters before
a call. In non-thumb2 mode it uses a constant pool load to materialize the
trip count. For targets that need movt instead (e.g. Native Client), use
the same code as in thumb2 mode to materialize the trip count.

http://reviews.llvm.org/D8442

Files:
  lib/Target/ARM/ARMISelLowering.cpp
  test/CodeGen/ARM/struct_byval.ll

Index: lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- lib/Target/ARM/ARMISelLowering.cpp
+++ lib/Target/ARM/ARMISelLowering.cpp
@@ -7140,16 +7140,20 @@
 
   // Load an immediate to varEnd.
   unsigned varEnd = MRI.createVirtualRegister(TRC);
-  if (IsThumb2) {
+  if (IsThumb2 || Subtarget->useMovt(*MF)) {
     unsigned Vtmp = varEnd;
     if ((LoopSize & 0xFFFF0000) != 0)
       Vtmp = MRI.createVirtualRegister(TRC);
-    AddDefaultPred(BuildMI(BB, dl, TII->get(ARM::t2MOVi16), Vtmp)
-                       .addImm(LoopSize & 0xFFFF));
+    AddDefaultPred(BuildMI(BB, dl,
+                           TII->get(IsThumb2 ? ARM::t2MOVi16 : ARM::MOVi16),
+                           Vtmp).addImm(LoopSize & 0xFFFF));
 
     if ((LoopSize & 0xFFFF0000) != 0)
-      AddDefaultPred(BuildMI(BB, dl, TII->get(ARM::t2MOVTi16), varEnd)
-                         .addReg(Vtmp).addImm(LoopSize >> 16));
+      AddDefaultPred(BuildMI(BB, dl,
+                             TII->get(IsThumb2 ? ARM::t2MOVTi16 : ARM::MOVTi16),
+                             varEnd)
+                         .addReg(Vtmp)
+                         .addImm(LoopSize >> 16));
   } else {
     MachineConstantPool *ConstantPool = MF->getConstantPool();
     Type *Int32Ty = Type::getInt32Ty(MF->getFunction()->getContext());
Index: test/CodeGen/ARM/struct_byval.ll
===================================================================
--- test/CodeGen/ARM/struct_byval.ll
+++ test/CodeGen/ARM/struct_byval.ll
@@ -1,6 +1,10 @@
 ; RUN: llc < %s -mtriple=armv7-apple-ios6.0 | FileCheck %s
 ; RUN: llc < %s -mtriple=thumbv7-apple-ios6.0 | FileCheck %s -check-prefix=THUMB
 
+; For NaCl (where we always want movt) ensure no const pool loads are generated.
+; RUN: llc < %s -mtriple=armv7-unknown-nacl-gnueabi | FileCheck %s -check-prefix=NACL
+; NACL-NOT: .LCPI
+
 ; rdar://9877866
 %struct.SmallStruct = type { i32, [8 x i32], [37 x i8] }
 %struct.LargeStruct = type { i32, [1001 x i8], [300 x i32] }

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