Add ExtractValue instruction to SimplifyCFG's ComputeSpeculationCost

Since ExtractValue is not included in ComputeSpeculationCost CFGs containing
ExtractValueInsts cannot be simplified. In particular this interacts with
InstCombineCompare's tendency to insert add.with.overflow intrinsics for
certain idiomatic math operations, preventing optimization.

This patch adds ExtractValue to the ComputeSpeculationCost. Test case included

rdar://14853450

llvm-svn: 208434

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -213,6 +213,7 @@ static unsigned ComputeSpeculationCost(const User *I) {
     if (!cast<GEPOperator>(I)->hasAllConstantIndices())
       return UINT_MAX;
     return 1;
+  case Instruction::ExtractValue:
   case Instruction::Load:
   case Instruction::Add:
   case Instruction::Sub:

test/Transforms/SimplifyCFG/extract-cost.ll

@@ -0,0 +1,22 @@
+; RUN: opt -simplifycfg -S  < %s | FileCheck %s
+
+declare { i32, i1 } @llvm.uadd.with.overflow.i32(i32, i32) #1
+
+define i32 @f(i32 %a, i32 %b) #0 {
+entry:
+  %uadd = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+  %cmp = extractvalue { i32, i1 } %uadd, 1
+  br i1 %cmp, label %return, label %if.end
+
+if.end:                                           ; preds = %entry
+  %0 = extractvalue { i32, i1 } %uadd, 0
+  br label %return
+
+return:                                           ; preds = %entry, %if.end
+  %retval.0 = phi i32 [ %0, %if.end ], [ 0, %entry ]
+  ret i32 %retval.0
+
+; CHECK-LABEL: @f(
+; CHECK-NOT: phi
+; CHECK: select
+}