[PATCH] Make bitcast, extractelement, and insertelement considered cheap for speculation in SimplifyCFG.

[Matt Arsenault]

Hi nadav,

This help fold more branches into selects. 
On R600, vectors are cheap and anything that helps 
remove branches is very good.
    
I don't know why this doesn't use the TTI for this cost 
calculation or if it should.

http://llvm-reviews.chandlerc.com/D2218

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/speculate-vector-ops.ll

Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -224,6 +224,9 @@
   case Instruction::Trunc:
   case Instruction::ZExt:
   case Instruction::SExt:
+  case Instruction::BitCast:
+  case Instruction::ExtractElement:
+  case Instruction::InsertElement:
     return 1; // These are all cheap.
 
   case Instruction::Call:
Index: test/Transforms/SimplifyCFG/speculate-vector-ops.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/speculate-vector-ops.ll
@@ -0,0 +1,60 @@
+; RUN: opt -S -simplifycfg < %s | FileCheck %s
+
+define i32 @speculate_vector_extract(i32 %d, <4 x i32> %v) #0 {
+; CHECK-LABEL: @speculate_vector_extract(
+; CHECK-NOT: br
+entry:
+  %conv = insertelement <4 x i32> undef, i32 %d, i32 0
+  %conv2 = insertelement <4 x i32> %conv, i32 %d, i32 1
+  %conv3 = insertelement <4 x i32> %conv2, i32 %d, i32 2
+  %conv4 = insertelement <4 x i32> %conv3, i32 %d, i32 3
+  %tmp6 = add nsw <4 x i32> %conv4, <i32 0, i32 -1, i32 -2, i32 -3>
+  %cmp = icmp eq <4 x i32> %tmp6, zeroinitializer
+  %cmp.ext = sext <4 x i1> %cmp to <4 x i32>
+  %tmp8 = extractelement <4 x i32> %cmp.ext, i32 0
+  %tobool = icmp eq i32 %tmp8, 0
+  br i1 %tobool, label %cond.else, label %cond.then
+
+return:                                           ; preds = %cond.end28
+  ret i32 %cond32
+
+cond.then:                                        ; preds = %entry
+  %tmp10 = extractelement <4 x i32> %v, i32 0
+  br label %cond.end
+
+cond.else:                                        ; preds = %entry
+  %tmp12 = extractelement <4 x i32> %v, i32 3
+  br label %cond.end
+
+cond.end:                                         ; preds = %cond.else, %cond.then
+  %cond = phi i32 [ %tmp10, %cond.then ], [ %tmp12, %cond.else ]
+  %tmp14 = extractelement <4 x i32> %cmp.ext, i32 1
+  %tobool15 = icmp eq i32 %tmp14, 0
+  br i1 %tobool15, label %cond.else17, label %cond.then16
+
+cond.then16:                                      ; preds = %cond.end
+  %tmp20 = extractelement <4 x i32> %v, i32 1
+  br label %cond.end18
+
+cond.else17:                                      ; preds = %cond.end
+  br label %cond.end18
+
+cond.end18:                                       ; preds = %cond.else17, %cond.then16
+  %cond22 = phi i32 [ %tmp20, %cond.then16 ], [ %cond, %cond.else17 ]
+  %tmp24 = extractelement <4 x i32> %cmp.ext, i32 2
+  %tobool25 = icmp eq i32 %tmp24, 0
+  br i1 %tobool25, label %cond.else27, label %cond.then26
+
+cond.then26:                                      ; preds = %cond.end18
+  %tmp30 = extractelement <4 x i32> %v, i32 2
+  br label %cond.end28
+
+cond.else27:                                      ; preds = %cond.end18
+  br label %cond.end28
+
+cond.end28:                                       ; preds = %cond.else27, %cond.then26
+  %cond32 = phi i32 [ %tmp30, %cond.then26 ], [ %cond22, %cond.else27 ]
+  br label %return
+}
+
+attributes #0 = { nounwind }
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