Recommit "[SCCP] Remove forcedconstant, go to overdefined instead"

This includes a fix for cases where things get marked as overdefined in
ResolvedUndefsIn, but we later discover a constant. To avoid crashing,
we consistently bail out on overdefined values in the visitors. This is
similar to the previous behavior with forcedconstant.

This reverts the revert commit 02b72f564c8be0b4f4337d5c4a3fcf7e8018a818.
diff --git a/llvm/test/Transforms/SCCP/logical-nuke.ll b/llvm/test/Transforms/SCCP/logical-nuke.ll
index 6ca16de4..5152e12 100644
--- a/llvm/test/Transforms/SCCP/logical-nuke.ll
+++ b/llvm/test/Transforms/SCCP/logical-nuke.ll
@@ -1,39 +1,47 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -sccp -S | FileCheck %s
 
 ; Test that SCCP has basic knowledge of when and/or/mul nuke overdefined values.
 
-; CHECK-LABEL: test
-; CHECK: ret i32 0
  define i32 @test(i32 %X) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    ret i32 0
+;
   %Y = and i32 %X, 0
   ret i32 %Y
 }
 
-; CHECK-LABEL: test2
-; CHECK: ret i32 -1
 define i32 @test2(i32 %X) {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:    ret i32 -1
+;
   %Y = or i32 -1, %X
   ret i32 %Y
 }
 
-; CHECK-LABEL: test3
-; CHECK: ret i32 0
 define i32 @test3(i32 %X) {
+; CHECK-LABEL: @test3(
+; CHECK-NEXT:    [[Y:%.*]] = and i32 undef, [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[Y]]
+;
   %Y = and i32 undef, %X
   ret i32 %Y
 }
 
-; CHECK-LABEL: test4
-; CHECK: ret i32 -1
 define i32 @test4(i32 %X) {
+; CHECK-LABEL: @test4(
+; CHECK-NEXT:    [[Y:%.*]] = or i32 [[X:%.*]], undef
+; CHECK-NEXT:    ret i32 [[Y]]
+;
   %Y = or i32 %X, undef
   ret i32 %Y
 }
 
 ; X * 0 = 0 even if X is overdefined.
-; CHECK-LABEL: test5
-; CHECK: ret i32 0
 define i32 @test5(i32 %foo) {
+; CHECK-LABEL: @test5(
+; CHECK-NEXT:    ret i32 0
+;
   %patatino = mul i32 %foo, 0
   ret i32 %patatino
 }