From 9f33e3748e76d9510c53fe2f74af07392b9c75b1 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Wed, 2 Sep 2015 19:17:25 +0000
Subject: [PATCH] use "unpredictable" metadata in SelectionDAG when splitting
 compares

This patch uses the metadata defined in D12341 to avoid creating an unpredictable branch.

Differential Revision: http://reviews.llvm.org/D12343



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246691 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../SelectionDAG/SelectionDAGBuilder.cpp      |  9 +++---
 test/CodeGen/X86/or-branch.ll                 | 30 +++++++++++++++++--
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 997fa1ae061..7c1706f6edc 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1625,11 +1625,12 @@ void SelectionDAGBuilder::visitBr(const BranchInst &I) {
   //     jle foo
   //
   if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(CondVal)) {
-    if (!DAG.getTargetLoweringInfo().isJumpExpensive() &&
-        BOp->hasOneUse() && (BOp->getOpcode() == Instruction::And ||
-                             BOp->getOpcode() == Instruction::Or)) {
+    Instruction::BinaryOps Opcode = BOp->getOpcode();
+    if (!DAG.getTargetLoweringInfo().isJumpExpensive() && BOp->hasOneUse() &&
+        !I.getMetadata(LLVMContext::MD_unpredictable) &&
+        (Opcode == Instruction::And || Opcode == Instruction::Or)) {
       FindMergedConditions(BOp, Succ0MBB, Succ1MBB, BrMBB, BrMBB,
-                           BOp->getOpcode(), getEdgeWeight(BrMBB, Succ0MBB),
+                           Opcode, getEdgeWeight(BrMBB, Succ0MBB),
                            getEdgeWeight(BrMBB, Succ1MBB));
       // If the compares in later blocks need to use values not currently
       // exported from this block, export them now.  This block should always
diff --git a/test/CodeGen/X86/or-branch.ll b/test/CodeGen/X86/or-branch.ll
index 9db948adb46..4899a0fc7e8 100644
--- a/test/CodeGen/X86/or-branch.ll
+++ b/test/CodeGen/X86/or-branch.ll
@@ -1,5 +1,5 @@
-; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=0 | FileCheck %s --check-prefix=JUMP2
-; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=1 | FileCheck %s --check-prefix=JUMP1
+; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=0 | FileCheck %s --check-prefix=JUMP2 --check-prefix=CHECK
+; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=1 | FileCheck %s --check-prefix=JUMP1 --check-prefix=CHECK
 
 define void @foo(i32 %X, i32 %Y, i32 %Z) nounwind {
 ; JUMP2-LABEL: foo:
@@ -25,4 +25,30 @@ UnifiedReturnBlock:
   ret void
 }
 
+; If the branch is unpredictable, don't add another branch
+; regardless of whether they are expensive or not.
+
+define void @unpredictable(i32 %X, i32 %Y, i32 %Z) nounwind {
+; CHECK-LABEL: unpredictable:
+; CHECK-DAG:     sete
+; CHECK-DAG:     setl
+; CHECK:         orb
+; CHECK:         jne
+entry:
+  %tmp1 = icmp eq i32 %X, 0
+  %tmp3 = icmp slt i32 %Y, 5
+  %tmp4 = or i1 %tmp3, %tmp1
+  br i1 %tmp4, label %cond_true, label %UnifiedReturnBlock, !unpredictable !0
+
+cond_true:
+  %tmp5 = tail call i32 (...) @bar( )
+  ret void
+
+UnifiedReturnBlock:
+  ret void
+}
+
 declare i32 @bar(...)
+
+!0 = !{}
+
-- 
2.34.1