Add a very basic test for MachineBlockPlacement. This is essentially the

canonical example I used when developing it, and is one of the primary
motivating real-world use cases for __builtin_expect (when burried under
a macro).

I'm working on more test cases here, but I'm trying to make sure both
that the pass is doing the right thing with the test cases and that they
aren't too brittle to changes elsewhere in the code generation pipeline.

Feedback and/or suggestions on how to test this are very welcome.
Especially feedback on whether testing the block comments is a good
strategy; I couldn't find any good examples to steal from but all the
other ideas I had were a lot uglier or more fragile.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142644 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/block-placement.ll

@@ -0,0 +1,75 @@
+; RUN: llc -march=x86 -enable-block-placement < %s | FileCheck %s
+
+declare void @error(i32 %i, i32 %a, i32 %b)
+
+define i32 @test1(i32 %i, i32* %a, i32 %b) {
+; Test a chain of ifs, where the block guarded by the if is error handling code
+; that is not expected to run.
+; CHECK: test1:
+; CHECK: %entry
+; CHECK: %else1
+; CHECK: %else2
+; CHECK: %else3
+; CHECK: %else4
+; CHECK: %exit
+; CHECK: %then1
+; CHECK: %then2
+; CHECK: %then3
+; CHECK: %then4
+; CHECK: %then5
+
+entry:
+  %gep1 = getelementptr i32* %a, i32 1
+  %val1 = load i32* %gep1
+  %cond1 = icmp ugt i32 %val1, 1
+  br i1 %cond1, label %then1, label %else1, !prof !0
+
+then1:
+  call void @error(i32 %i, i32 1, i32 %b)
+  br label %else1
+
+else1:
+  %gep2 = getelementptr i32* %a, i32 2
+  %val2 = load i32* %gep2
+  %cond2 = icmp ugt i32 %val2, 2
+  br i1 %cond2, label %then2, label %else2, !prof !0
+
+then2:
+  call void @error(i32 %i, i32 1, i32 %b)
+  br label %else2
+
+else2:
+  %gep3 = getelementptr i32* %a, i32 3
+  %val3 = load i32* %gep3
+  %cond3 = icmp ugt i32 %val3, 3
+  br i1 %cond3, label %then3, label %else3, !prof !0
+
+then3:
+  call void @error(i32 %i, i32 1, i32 %b)
+  br label %else3
+
+else3:
+  %gep4 = getelementptr i32* %a, i32 4
+  %val4 = load i32* %gep4
+  %cond4 = icmp ugt i32 %val4, 4
+  br i1 %cond4, label %then4, label %else4, !prof !0
+
+then4:
+  call void @error(i32 %i, i32 1, i32 %b)
+  br label %else4
+
+else4:
+  %gep5 = getelementptr i32* %a, i32 3
+  %val5 = load i32* %gep5
+  %cond5 = icmp ugt i32 %val5, 3
+  br i1 %cond5, label %then5, label %exit, !prof !0
+
+then5:
+  call void @error(i32 %i, i32 1, i32 %b)
+  br label %exit
+
+exit:
+  ret i32 %b
+}
+
+!0 = metadata !{metadata !"branch_weights", i32 4, i32 64}