Replace constant conditional branches by unconditional branches

tests_lit/reader_tests/forwardref.ll

 ; Test use forward type references in function blocks.
 
 ; RUN: %p2i -i %s --insts | FileCheck %s
 ; RUN: llvm-as < %s | pnacl-freeze | pnacl-bcdis -no-records \
 ; RUN:              | FileCheck --check-prefix=DUMP %s
 ; RUN:   %p2i -i %s --args -notranslate -timing | \
 ; RUN:   FileCheck --check-prefix=NOIR %s
 
 define internal void @LoopCarriedDep() {
 b0:
@@ skipping 54 matching lines @@
 b6:
   ret void
 }
 
 ; CHECK:      define internal void @BackBranch(i32 %p0) {
 ; CHECK-NEXT: b0:
 ; CHECK-NEXT:   br label %b4
 ; CHECK-NEXT: b1:
 ; CHECK-NEXT:   %v0 = add i32 %p0, %v3
 ; CHECK-NEXT:   br label %b6
-; CHECK-NEXT: b2:
-; CHECK-NEXT:   %v1 = add i32 %p0, %v4
-; CHECK-NEXT:   br label %b6
-; CHECK-NEXT: b3:
-; CHECK-NEXT:   %v2 = add i32 %p0, %v3
-; CHECK-NEXT:   br label %b6
 ; CHECK-NEXT: b4:
 ; CHECK-NEXT:   %v3 = add i32 %p0, %p0
-; CHECK-NEXT:   br i1 true, label %b1, label %b5
-; CHECK-NEXT: b5:
-; CHECK-NEXT:   %v4 = add i32 %v3, %p0
-; CHECK-NEXT:   br i1 true, label %b2, label %b3
+; CHECK-NEXT:   br label %b1
 ; CHECK-NEXT: b6:
 ; CHECK-NEXT:   ret void
 ; CHECK-NEXT: }
 
 ; Snippet of bitcode objdump with forward type references (see "declare").
 ; DUMP:        function void @f1(i32 %p0) {  // BlockID = 12
 ; DUMP-NEXT:     blocks 7;
 ; DUMP-NEXT:     constants {  // BlockID = 11
 ; DUMP-NEXT:       i1: <@a0>
 ; DUMP-NEXT:         %c0 = i1 1; <@a1>
@@ skipping 15 matching lines @@
 ; DUMP-NEXT:     %v3 = add i32 %p0, %p0; <@a1>
 ; DUMP-NEXT:     br i1 %c0, label %b1, label %b5;
 ; DUMP-NEXT:   %b5:
 ; DUMP-NEXT:     %v4 = add i32 %v3, %p0; <@a1>
 ; DUMP-NEXT:     br i1 %c0, label %b2, label %b3;
 ; DUMP-NEXT:   %b6:
 ; DUMP-NEXT:     ret void; <@a3>
 ; DUMP-NEXT:   }
 
 ; NOIR: Total across all functions