[PowerPC/BlockPlacement] Allow target to provide a per-loop alignment preference

The existing code provided for specifying a global loop alignment preference.
However, the preferred loop alignment might depend on the loop itself. For
recent POWER cores, loops between 5 and 8 instructions should have 32-byte
alignment (while the others are better with 16-byte alignment) so that the
entire loop will fit in one i-cache line.

To support this, getPrefLoopAlignment has been made virtual, and can be
provided with an optional MachineLoop* so the target can inspect the loop
before answering the query. The default behavior, as before, is to return the
value set with setPrefLoopAlignment. MachineBlockPlacement now queries the
target for each loop instead of only once per function. There should be no
functional change for other targets.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225117 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 9a04d3c6c679f50c98dddb296e2551c18492b047..7a62d5d19e335ae4181e036816cec802c2536e23 100644 (file)
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -51,6 +51,7 @@ namespace llvm {
   class MachineFunction;
   class MachineInstr;
   class MachineJumpTableInfo;
+  class MachineLoop;
   class Mangler;
   class MCContext;
   class MCExpr;
@@ -929,7 +930,7 @@ public:
   }
 
   /// Return the preferred loop alignment.
-  unsigned getPrefLoopAlignment() const {
+  virtual unsigned getPrefLoopAlignment(MachineLoop *ML = nullptr) const {
     return PrefLoopAlignment;
   }
 
@@ -1336,7 +1337,8 @@ protected:
 
   /// Set the target's preferred loop alignment. Default alignment is zero, it
   /// means the target does not care about loop alignment.  The alignment is
-  /// specified in log2(bytes).
+  /// specified in log2(bytes). The target may also override
+  /// getPrefLoopAlignment to provide per-loop values.
   void setPrefLoopAlignment(unsigned Align) {
     PrefLoopAlignment = Align;
   }

diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index 08fd20036f045ba247b5decce11fd46b036f0c24..aaa7d9156976850ac1382304600ea2e8bd86544b 100644 (file)
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -1046,9 +1046,6 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
   if (F.getFunction()->getAttributes().
         hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize))
     return;
-  unsigned Align = TLI->getPrefLoopAlignment();
-  if (!Align)
-    return;  // Don't care about loop alignment.
   if (FunctionChain.begin() == FunctionChain.end())
     return;  // Empty chain.
 
@@ -1066,6 +1063,10 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
     if (!L)
       continue;
 
+    unsigned Align = TLI->getPrefLoopAlignment(L);
+    if (!Align)
+      continue;  // Don't care about loop alignment.
+
     // If the block is cold relative to the function entry don't waste space
     // aligning it.
     BlockFrequency Freq = MBFI->getBlockFreq(*BI);

diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index 8d8c32264dbbed6eefaf0a1401ba3df7515a463f..203a610a6bc6655b02cd6462464982a482336a45 100644 (file)
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -24,6 +24,7 @@
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
@@ -9049,6 +9050,40 @@ void PPCTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
   }
 }
 
+unsigned PPCTargetLowering::getPrefLoopAlignment(MachineLoop *ML) const {
+  switch (Subtarget.getDarwinDirective()) {
+  default: break;
+  case PPC::DIR_970:
+  case PPC::DIR_PWR4:
+  case PPC::DIR_PWR5:
+  case PPC::DIR_PWR5X:
+  case PPC::DIR_PWR6:
+  case PPC::DIR_PWR6X:
+  case PPC::DIR_PWR7:
+  case PPC::DIR_PWR8: {
+    if (!ML)
+      break;
+
+    const PPCInstrInfo *TII =
+      static_cast<const PPCInstrInfo *>(getTargetMachine().getSubtargetImpl()->
+                                          getInstrInfo());
+
+    // For small loops (between 5 and 8 instructions), align to a 32-byte
+    // boundary so that the entire loop fits in one instruction-cache line.
+    uint64_t LoopSize = 0;
+    for (auto I = ML->block_begin(), IE = ML->block_end(); I != IE; ++I)
+      for (auto J = (*I)->begin(), JE = (*I)->end(); J != JE; ++J)
+        LoopSize += TII->GetInstSizeInBytes(J);
+
+    if (LoopSize > 16 && LoopSize <= 32)
+      return 5;
+
+    break;
+  }
+  }
+
+  return TargetLowering::getPrefLoopAlignment(ML);
+}
 
 /// getConstraintType - Given a constraint, return the type of
 /// constraint it is for this target.

diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index b4b11d846e37019f0ad8814bf227c763ba8e96e5..d9142c7e7d03f6f934eea44e4612419c889ae9bd 100644 (file)
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -449,6 +449,8 @@ namespace llvm {
                                        const SelectionDAG &DAG,
                                        unsigned Depth = 0) const override;
 
+    unsigned getPrefLoopAlignment(MachineLoop *ML) const override;
+
     Instruction* emitLeadingFence(IRBuilder<> &Builder, AtomicOrdering Ord,
                                   bool IsStore, bool IsLoad) const override;
     Instruction* emitTrailingFence(IRBuilder<> &Builder, AtomicOrdering Ord,

diff --git a/test/CodeGen/PowerPC/code-align.ll b/test/CodeGen/PowerPC/code-align.ll
index 5550547d010d6ce90435a0b67b31448cc31d51ab..306230be500532dddd4ffb0b7b0a8aae890b78e2 100644 (file)
--- a/test/CodeGen/PowerPC/code-align.ll
+++ b/test/CodeGen/PowerPC/code-align.ll
@@ -1,15 +1,15 @@
 ; RUN: llc -mcpu=ppc64 < %s | FileCheck %s -check-prefix=GENERIC
-; RUN: llc -mcpu=970 < %s | FileCheck %s -check-prefix=BASIC
+; RUN: llc -mcpu=970 < %s | FileCheck %s -check-prefix=PWR
 ; RUN: llc -mcpu=a2 < %s | FileCheck %s -check-prefix=BASIC
 ; RUN: llc -mcpu=e500mc < %s | FileCheck %s -check-prefix=BASIC
 ; RUN: llc -mcpu=e5500 < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr4 < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr5 < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr5x < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr6 < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr6x < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr7 < %s | FileCheck %s -check-prefix=BASIC
-; RUN: llc -mcpu=pwr8 < %s | FileCheck %s -check-prefix=BASIC
+; RUN: llc -mcpu=pwr4 < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr5 < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr5x < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr6 < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr6x < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr7 < %s | FileCheck %s -check-prefix=PWR
+; RUN: llc -mcpu=pwr8 < %s | FileCheck %s -check-prefix=PWR
 target datalayout = "E-m:e-i64:64-n32:64"
 target triple = "powerpc64-unknown-linux-gnu"
 
@@ -21,10 +21,13 @@ entry:
 
 ; GENERIC-LABEL: .globl  foo
 ; BASIC-LABEL: .globl  foo
+; PWR-LABEL: .globl  foo
 ; GENERIC: .align  2
 ; BASIC: .align  4
+; PWR: .align  4
 ; GENERIC: @foo
 ; BASIC: @foo
+; PWR: @foo
 }
 
 ; Function Attrs: nounwind
@@ -34,12 +37,16 @@ entry:
 
 ; GENERIC-LABEL: @loop
 ; BASIC-LABEL: @loop
+; PWR-LABEL: @loop
 ; GENERIC: mtctr
 ; BASIC: mtctr
+; PWR: mtctr
 ; GENERIC-NOT: .align
 ; BASIC: .align  4
+; PWR: .align  4
 ; GENERIC: bdnz
 ; BASIC: bdnz
+; PWR: bdnz
 
 vector.body:                                      ; preds = %vector.body, %entry
   %index = phi i64 [ 0, %entry ], [ %index.next, %vector.body ]
@@ -60,6 +67,38 @@ for.end:                                          ; preds = %vector.body
   ret void
 }
 
+; Function Attrs: nounwind
+define void @sloop(i32 signext %x, i32* nocapture %a) #1 {
+entry:
+  br label %for.body
+
+; GENERIC-LABEL: @sloop
+; BASIC-LABEL: @sloop
+; PWR-LABEL: @sloop
+; GENERIC: mtctr
+; BASIC: mtctr
+; PWR: mtctr
+; GENERIC-NOT: .align
+; BASIC: .align  4
+; PWR: .align  5
+; GENERIC: bdnz
+; BASIC: bdnz
+; PWR: bdnz
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
+  %0 = load i32* %arrayidx, align 4
+  %add = add nsw i32 %0, 4
+  store i32 %add, i32* %arrayidx, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv.next, 2048
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
 attributes #0 = { nounwind readnone }
 attributes #1 = { nounwind }