ARM: decide whether to use movw/movt based on "minsize" attribute.

llvm-svn: 196102

lib/Target/ARM/ARMBaseInstrInfo.cpp

@@ -1859,12 +1859,12 @@ void llvm::emitARMRegPlusImmediate(MachineBasicBlock &MBB,
   }
 }
 
-bool llvm::tryFoldSPUpdateIntoPushPop(MachineFunction &MF,
-                                      MachineInstr *MI,
+bool llvm::tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
+                                      MachineFunction &MF, MachineInstr *MI,
                                       unsigned NumBytes) {
   // This optimisation potentially adds lots of load and store
   // micro-operations, it's only really a great benefit to code-size.
-  if (!MF.getFunction()->hasFnAttribute(Attribute::MinSize))
+  if (!Subtarget.isMinSize())
     return false;
 
   // If only one register is pushed/popped, LLVM can use an LDR/STR

lib/Target/ARM/ARMBaseInstrInfo.h

@@ -417,7 +417,8 @@ void emitThumbRegPlusImmediate(MachineBasicBlock &MBB,
 /// NumBytes. This can save a few bytes per function in code-size, but
 /// obviously generates more memory traffic. As such, it only takes
 /// effect in functions being optimised for size.
-bool tryFoldSPUpdateIntoPushPop(MachineFunction &MF, MachineInstr *MI,
+bool tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
+                                MachineFunction &MF, MachineInstr *MI,
                                 unsigned NumBytes);
 
 /// rewriteARMFrameIndex / rewriteT2FrameIndex -

lib/Target/ARM/ARMFrameLowering.cpp

@@ -256,7 +256,7 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
 
   if (NumBytes) {
     // Adjust SP after all the callee-save spills.
-    if (tryFoldSPUpdateIntoPushPop(MF, LastPush, NumBytes))
+    if (tryFoldSPUpdateIntoPushPop(STI, MF, LastPush, NumBytes))
       FramePtrOffsetInPush += NumBytes;
     else
       emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes,
@@ -434,7 +434,8 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
                                  ARM::SP)
             .addReg(FramePtr));
       }
-    } else if (NumBytes && !tryFoldSPUpdateIntoPushPop(MF, FirstPop, NumBytes))
+    } else if (NumBytes &&
+               !tryFoldSPUpdateIntoPushPop(STI, MF, FirstPop, NumBytes))
         emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes);
 
     // Increment past our save areas.

lib/Target/ARM/ARMISelLowering.cpp

@@ -1745,8 +1745,7 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // FIXME: handle tail calls differently.
   unsigned CallOpc;
-  bool HasMinSizeAttr = MF.getFunction()->getAttributes().
-    hasAttribute(AttributeSet::FunctionIndex, Attribute::MinSize);
+  bool HasMinSizeAttr = Subtarget->isMinSize();
   if (Subtarget->isThumb()) {
     if ((!isDirect || isARMFunc) && !Subtarget->hasV5TOps())
       CallOpc = ARMISD::CALL_NOLINK;

lib/Target/ARM/ARMSubtarget.cpp

@@ -102,6 +102,7 @@ void ARMSubtarget::initializeEnvironment() {
   HasVFPv4 = false;
   HasFPARMv8 = false;
   HasNEON = false;
+  MinSize = false;
   UseNEONForSinglePrecisionFP = false;
   UseMulOps = UseFusedMulOps;
   SlowFPVMLx = false;
@@ -151,6 +152,9 @@ void ARMSubtarget::resetSubtargetFeatures(const MachineFunction *MF) {
     initializeEnvironment();
     resetSubtargetFeatures(CPU, FS);
   }
+
+  MinSize =
+      FnAttrs.hasAttribute(AttributeSet::FunctionIndex, Attribute::MinSize);
 }
 
 void ARMSubtarget::resetSubtargetFeatures(StringRef CPU, StringRef FS) {

lib/Target/ARM/ARMSubtarget.h

@@ -64,6 +64,10 @@ protected:
   bool HasFPARMv8;
   bool HasNEON;
 
+  /// MinSize - True if the function being compiled has the "minsize" attribute
+  /// and should be optimised for size at the expense of speed.
+  bool MinSize;
+
   /// UseNEONForSinglePrecisionFP - if the NEONFP attribute has been
   /// specified. Use the method useNEONForSinglePrecisionFP() to
   /// determine if NEON should actually be used.
@@ -270,6 +274,7 @@ public:
   bool hasCrypto() const { return HasCrypto; }
   bool hasCRC() const { return HasCRC; }
   bool hasVirtualization() const { return HasVirtualization; }
+  bool isMinSize() const { return MinSize; }
   bool useNEONForSinglePrecisionFP() const {
     return hasNEON() && UseNEONForSinglePrecisionFP; }
 
@@ -327,7 +332,7 @@ public:
 
   bool isR9Reserved() const { return IsR9Reserved; }
 
-  bool useMovt() const { return UseMovt && hasV6T2Ops(); }
+  bool useMovt() const { return UseMovt && !isMinSize(); }
   bool supportsTailCall() const { return SupportsTailCall; }
 
   bool allowsUnalignedMem() const { return AllowsUnalignedMem; }

lib/Target/ARM/Thumb1FrameLowering.cpp

@@ -165,7 +165,7 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
   NumBytes = DPRCSOffset;
 
   int FramePtrOffsetInBlock = 0;
-  if (tryFoldSPUpdateIntoPushPop(MF, prior(MBBI), NumBytes)) {
+  if (tryFoldSPUpdateIntoPushPop(STI, MF, prior(MBBI), NumBytes)) {
     FramePtrOffsetInBlock = NumBytes;
     NumBytes = 0;
   }
@@ -291,9 +291,9 @@ void Thumb1FrameLowering::emitEpilogue(MachineFunction &MF,
           &MBB.front() != MBBI &&
           prior(MBBI)->getOpcode() == ARM::tPOP) {
         MachineBasicBlock::iterator PMBBI = prior(MBBI);
-        if (!tryFoldSPUpdateIntoPushPop(MF, PMBBI, NumBytes))
+        if (!tryFoldSPUpdateIntoPushPop(STI, MF, PMBBI, NumBytes))
           emitSPUpdate(MBB, PMBBI, TII, dl, *RegInfo, NumBytes);
-      } else if (!tryFoldSPUpdateIntoPushPop(MF, MBBI, NumBytes))
+      } else if (!tryFoldSPUpdateIntoPushPop(STI, MF, MBBI, NumBytes))
         emitSPUpdate(MBB, MBBI, TII, dl, *RegInfo, NumBytes);
     }
   }

lib/Target/ARM/Thumb2SizeReduction.cpp

@@ -1012,8 +1012,7 @@ bool Thumb2SizeReduce::runOnMachineFunction(MachineFunction &MF) {
   AttributeSet FnAttrs = MF.getFunction()->getAttributes();
   OptimizeSize = FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
                                       Attribute::OptimizeForSize);
-  MinimizeSize = FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
-                                      Attribute::MinSize);
+  MinimizeSize = STI->isMinSize();
 
   BlockInfo.clear();
   BlockInfo.resize(MF.getNumBlockIDs());

test/CodeGen/ARM/minsize-litpools.ll

@@ -0,0 +1,26 @@
+; RUN: llc -mtriple=thumbv7s %s -o -  | FileCheck %s
+; RUN: llc -mtriple=armv7s %s -o -  | FileCheck %s
+
+; CodeGen should be able to set and reset the MinSize subtarget-feature, and
+; make use of it in deciding whether to use MOVW/MOVT for global variables or a
+; lit-pool load (saving roughly 2 bytes of code).
+
+@var = global i32 0
+
+define i32 @small_global() minsize {
+; CHECK-LABEL: small_global:
+; CHECK: ldr r[[GLOBDEST:[0-9]+]], {{.?LCPI0_0}}
+; CHECK: ldr r0, [r[[GLOBDEST]]]
+
+  %val = load i32* @var
+  ret i32 %val
+}
+
+define i32 @big_global() {
+; CHECK-LABEL: big_global:
+; CHECK: movw [[GLOBDEST:r[0-9]+]], :lower16:var
+; CHECK: movt [[GLOBDEST]], :upper16:var
+
+  %val = load i32* @var
+  ret i32 %val
+}