[FastISel][X86] - Add branch weights

Add branch weights to branch instructions, so that the following passes can optimize based on it (i.e. basic block ordering). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210863 91177308-0d34-0410-b5e6-96231b3b80d8
stryku · Jun 13, 2014 · 7f8d138 · 7f8d138
1 parent f7a2d5e
commit 7f8d138
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Showing 3 changed files with 41 additions and 5 deletions.
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -42,6 +42,7 @@
 #include "llvm/CodeGen/FastISel.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/Loads.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
@@ -981,7 +982,6 @@ FastISel::SelectInstruction(const Instruction *I) {
 /// the CFG.
 void
 FastISel::FastEmitBranch(MachineBasicBlock *MSucc, DebugLoc DbgLoc) {
-
   if (FuncInfo.MBB->getBasicBlock()->size() > 1 &&
       FuncInfo.MBB->isLayoutSuccessor(MSucc)) {
     // For more accurate line information if this is the only instruction
@@ -992,7 +992,11 @@ FastISel::FastEmitBranch(MachineBasicBlock *MSucc, DebugLoc DbgLoc) {
     TII.InsertBranch(*FuncInfo.MBB, MSucc, nullptr,
                      SmallVector<MachineOperand, 0>(), DbgLoc);
   }
-  FuncInfo.MBB->addSuccessor(MSucc);
+  uint32_t BranchWeight = 0;
+  if (FuncInfo.BPI)
+    BranchWeight = FuncInfo.BPI->getEdgeWeight(FuncInfo.MBB->getBasicBlock(),
+                                               MSucc->getBasicBlock());
+  FuncInfo.MBB->addSuccessor(MSucc, BranchWeight);
 }
 
 /// SelectFNeg - Emit an FNeg operation.

diff --git a/lib/Target/X86/X86FastISel.cpp b/lib/Target/X86/X86FastISel.cpp
@@ -20,6 +20,7 @@
 #include "X86RegisterInfo.h"
 #include "X86Subtarget.h"
 #include "X86TargetMachine.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/FastISel.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
@@ -1206,7 +1207,11 @@ bool X86FastISel::X86SelectBranch(const Instruction *I) {
       }
 
       FastEmitBranch(FalseMBB, DbgLoc);
-      FuncInfo.MBB->addSuccessor(TrueMBB);
+      uint32_t BranchWeight = 0;
+      if (FuncInfo.BPI)
+        BranchWeight = FuncInfo.BPI->getEdgeWeight(BI->getParent(),
+                                                   TrueMBB->getBasicBlock());
+      FuncInfo.MBB->addSuccessor(TrueMBB, BranchWeight);
       return true;
     }
   } else if (TruncInst *TI = dyn_cast<TruncInst>(BI->getCondition())) {
@@ -1238,7 +1243,11 @@ bool X86FastISel::X86SelectBranch(const Instruction *I) {
         BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(JmpOpc))
           .addMBB(TrueMBB);
         FastEmitBranch(FalseMBB, DbgLoc);
-        FuncInfo.MBB->addSuccessor(TrueMBB);
+        uint32_t BranchWeight = 0;
+        if (FuncInfo.BPI)
+          BranchWeight = FuncInfo.BPI->getEdgeWeight(BI->getParent(),
+                                                     TrueMBB->getBasicBlock());
+        FuncInfo.MBB->addSuccessor(TrueMBB, BranchWeight);
         return true;
       }
     }
@@ -1255,7 +1264,11 @@ bool X86FastISel::X86SelectBranch(const Instruction *I) {
   BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(X86::JNE_4))
     .addMBB(TrueMBB);
   FastEmitBranch(FalseMBB, DbgLoc);
-  FuncInfo.MBB->addSuccessor(TrueMBB);
+  uint32_t BranchWeight = 0;
+  if (FuncInfo.BPI)
+    BranchWeight = FuncInfo.BPI->getEdgeWeight(BI->getParent(),
+                                               TrueMBB->getBasicBlock());
+  FuncInfo.MBB->addSuccessor(TrueMBB, BranchWeight);
   return true;
 }
 

diff --git a/test/CodeGen/X86/fast-isel-branch_weights.ll b/test/CodeGen/X86/fast-isel-branch_weights.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s                             -mtriple=x86_64-apple-darwin10 | FileCheck %s
+; RUN: llc < %s -fast-isel -fast-isel-abort -mtriple=x86_64-apple-darwin10 | FileCheck %s
+
+; Test if the BBs are reordred according to their branch weights.
+define i64 @branch_weights_test(i64 %a, i64 %b) {
+; CHECK-LABEL: branch_weights_test
+; CHECK-LABEL: success
+; CHECK-LABEL: fail
+  %1 = icmp ult i64 %a, %b
+  br i1 %1, label %fail, label %success, !prof !0
+
+fail:
+  ret i64 -1
+
+success:
+  ret i64 0
+}
+
+!0 = metadata !{metadata !"branch_weights", i32 0, i32 2147483647}