Add forward instruction declaration to Subzero bitcode reader.

tests_lit/reader_tests/forwardref.ll

+; Test use forward type references in function blocks.
+
+; RUN: llvm-as < %s | pnacl-freeze -allow-local-symbol-tables \
+; RUN:              | %llvm2ice -notranslate -verbose=inst -build-on-read \
+; RUN:                -allow-pnacl-reader-error-recovery \
+; RUN:                -allow-local-symbol-tables \
+; RUN:              | FileCheck %s
+
+; RUN: llvm-as < %s | pnacl-freeze | pnacl-bcdis -no-records \
+; RUN:              | FileCheck --check-prefix=DUMP %s
+
+define void @LoopCarriedDep() {
+b0:
+  %v0 = add i32 1, 2
+  br label %b1
+b1:
+  %v1 = phi i32 [%v0, %b0], [%v2, %b1]
+  %v2 = add i32 %v1, 1
+  br label %b1
+}
+
+; CHECK:      define void @LoopCarriedDep() {
+; CHECK-NEXT: b0:
+; CHECK-NEXT:   %v0 = add i32 1, 2
+; CHECK-NEXT:   br label %b1
+; CHECK-NEXT: b1:
+; CHECK-NEXT:   %v1 = phi i32 [ %v0, %b0 ], [ %v2, %b1 ]
+; CHECK-NEXT:   %v2 = add i32 %v1, 1
+; CHECK-NEXT:   br label %b1
+; CHECK-NEXT: }
+
+; Snippet of bitcode objdump with forward type reference (see "declare").
+; DUMP:        function void @f0() {  // BlockID = 12
+; DUMP-NEXT:     blocks 2;
+; DUMP-NEXT:     constants {  // BlockID = 11
+; DUMP-NEXT:       i32: <@a0>
+; DUMP-NEXT:         %c0 = i32 1; <@a1>
+; DUMP-NEXT:         %c1 = i32 2; <@a1>
+; DUMP-NEXT:       }
+; DUMP-NEXT:   %b0:
+; DUMP-NEXT:     %v0 = add i32 %c0, %c1; <@a1>
+; DUMP-NEXT:     br label %b1;
+; DUMP-NEXT:   %b1:
+; DUMP-NEXT:     declare i32 %v2; <@a6>
+; DUMP-NEXT:     %v1 = phi i32 [%v0, %b0], [%v2, %b1];
+; DUMP-NEXT:     %v2 = add i32 %v1, %c0; <@a1>
+; DUMP-NEXT:     br label %b1;
+; DUMP-NEXT:   }
+
+define void @BackBranch(i32 %p0) {
+b0:
+  br label %b4
+b1:
+  %v0 = add i32 %p0, %v3
+  br label %b6
+b2:
+  %v1 = add i32 %p0, %v4
+  br label %b6
+b3:
+  %v2 = add i32 %p0, %v3 ; No forward declare, already done!
+  br label %b6
+b4:
+  %v3 = add i32 %p0, %p0
+  br i1 1, label %b1, label %b5
+b5:
+  %v4 = add i32 %v3, %p0
+  br i1 1, label %b2, label %b3
+b6:
+  ret void
+}
+
+; CHECK:      define 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: 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>
+; DUMP-NEXT:       }
+; DUMP-NEXT:   %b0:
+; DUMP-NEXT:     br label %b4;
+; DUMP-NEXT:   %b1:
+; DUMP-NEXT:     declare i32 %v3; <@a6>
+; DUMP-NEXT:     %v0 = add i32 %p0, %v3; <@a1>
+; DUMP-NEXT:     br label %b6;
+; DUMP-NEXT:   %b2:
+; DUMP-NEXT:     declare i32 %v4; <@a6>
+; DUMP-NEXT:     %v1 = add i32 %p0, %v4; <@a1>
+; DUMP-NEXT:     br label %b6;
+; DUMP-NEXT:   %b3:
+; DUMP-NEXT:     %v2 = add i32 %p0, %v3; <@a1>
+; DUMP-NEXT:     br label %b6;
+; DUMP-NEXT:   %b4:
+; 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:   }