From 9b61c550c2f1fa889163a338f5d6c02b50fe961c Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Thu, 24 Feb 2011 22:46:11 +0000
Subject: [PATCH] SimplifyCFG: GEPs with constant indices are cheap enough to
 be executed unconditionally.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126445 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp      |  5 +++++
 test/Transforms/SimplifyCFG/select-gep.ll | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 test/Transforms/SimplifyCFG/select-gep.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index fb660dbfac1..c6708857cb5 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -247,6 +247,11 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
     if (PBB->getFirstNonPHIOrDbg() != I)
       return false;
     break;
+  case Instruction::GetElementPtr:
+    // GEPs are cheap if all indices are constant.
+    if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
+      return false;
+    break;
   case Instruction::Add:
   case Instruction::Sub:
   case Instruction::And:
diff --git a/test/Transforms/SimplifyCFG/select-gep.ll b/test/Transforms/SimplifyCFG/select-gep.ll
new file mode 100644
index 00000000000..6330ccdb291
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/select-gep.ll
@@ -0,0 +1,20 @@
+; RUN: opt -S -simplifycfg %s | FileCheck %s
+
+define i8* @test1(i8* %x) nounwind {
+entry:
+  %tmp1 = load i8* %x, align 1
+  %cmp = icmp eq i8 %tmp1, 47
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  %incdec.ptr = getelementptr inbounds i8* %x, i64 1
+  br label %if.end
+
+if.end:
+  %x.addr = phi i8* [ %incdec.ptr, %if.then ], [ %x, %entry ]
+  ret i8* %x.addr
+
+; CHECK: @test1
+; CHECK: %x.addr = select i1 %cmp, i8* %incdec.ptr, i8* %x
+; CHECK: ret i8* %x.addr
+}
-- 
2.34.1