[RewriteStatepointsForGC] Add tests for the base pointer identification algorithm

These tests cover the 'base object' identification and rewritting portion of RewriteStatepointsForGC.  These aren't completely exhaustive, but they've proven to be reasonable effective over time at finding regressions.

In the process of porting these tests over, I found my first "cleanup per llvm code style standards" bug.  We were relying on the order of iteration when testing the base pointers found for a derived pointer.  When we switched from std::set to DenseSet, this stopped being a safe assumption.  I'm suspecting I'm going to find more of those.  In particular, I'm now really wondering about the main iteration loop for this algorithm.  I need to go take a closer look at the assumptions there.

I'm not really happy with the fact these are testing what is essentially debug output (i.e. enabled via command line flags).  Suggestions for how to structure this better are very welcome.  



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230818 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/RewriteStatepointsForGC/base-pointers.ll

@@ -0,0 +1,98 @@
+; RUN: opt %s -rewrite-statepoints-for-gc -S 2>&1 | FileCheck %s
+
+declare i64 addrspace(1)* @generate_obj()
+declare void @use_obj(i64 addrspace(1)*)
+
+; The rewriting needs to make %obj loop variant by inserting a phi 
+; of the original value and it's relocation.
+define void @def_use_safepoint() gc "statepoint-example" {
+; CHECK-LABEL: def_use_safepoint
+entry:
+  %obj = call i64 addrspace(1)* @generate_obj()
+  br label %loop
+
+loop:
+; CHECK: phi i64 addrspace(1)* 
+; CHECK-DAG: [ %obj.relocated, %loop ]
+; CHECK-DAG: [ %obj, %entry ]
+  call void @use_obj(i64 addrspace(1)* %obj)
+  %safepoint_token = call i32 (void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(void ()* @do_safepoint, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0)
+  br label %loop
+}
+
+declare void @do_safepoint()
+
+declare void @parse_point(i64 addrspace(1)*)
+
+define i64 addrspace(1)* @test1(i32 %caller, i8 addrspace(1)* %a, i8 addrspace(1)* %b, i32 %unknown) gc "statepoint-example" {
+; CHECK-LABEL: test1
+ entry:
+  br i1 undef, label %left, label %right
+
+ left:
+  %a.cast = bitcast i8 addrspace(1)* %a to i64 addrspace(1)*
+; CHECK: left:
+; CHECK-NEXT: %a.cast = bitcast i8 addrspace(1)* %a to i64 addrspace(1)*
+; CHECK-NEXT: [[CAST_L:%.*]] = bitcast i8 addrspace(1)* %a to i64 addrspace(1)*
+
+; Our safepoint placement pass calls removeUnreachableBlocks, which does a bunch
+; of simplifications to branch instructions.  This bug is visible only when
+; there are multiple branches into the same block from the same predecessor, and
+; the following ceremony is to make that artefact survive a call to 
+; removeUnreachableBlocks.  As an example, "br i1 undef, label %merge, label %merge"
+; will get simplified to "br label %merge" by removeUnreachableBlocks.
+  switch i32 %unknown, label %right [ i32 0, label %merge
+                                      i32 1, label %merge
+                                      i32 5, label %merge
+                                      i32 3, label %right ]
+
+ right:
+  %b.cast = bitcast i8 addrspace(1)* %b to i64 addrspace(1)*
+  br label %merge
+; CHECK: right:
+; CHECK-NEXT: %b.cast = bitcast i8 addrspace(1)* %b to i64 addrspace(1)*
+; CHECK-NEXT: [[CAST_R:%.*]] = bitcast i8 addrspace(1)* %b to i64 addrspace(1)*
+
+ merge:
+; CHECK: merge:
+; CHECK-NEXT: %base_phi = phi i64 addrspace(1)* [ [[CAST_L]], %left ], [ [[CAST_L]], %left ], [ [[CAST_L]], %left ], [ [[CAST_R]], %right ], !is_base_value !0
+  %value = phi i64 addrspace(1)* [ %a.cast, %left], [ %a.cast, %left], [ %a.cast, %left], [ %b.cast, %right]
+  %safepoint_token = call i32 (void (i64 addrspace(1)*)*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidp1i64f(void (i64 addrspace(1)*)* @parse_point, i32 1, i32 0, i64 addrspace(1)* %value, i32 5, i32 0, i32 0, i32 0, i32 0, i32 0)
+
+  ret i64 addrspace(1)* %value
+}
+
+;; The purpose of this test is to ensure that when two live values share a
+;;  base defining value with inherent conflicts, we end up with a *single*
+;;  base phi/select per such node.  This is testing an optimization, not a
+;;  fundemental correctness criteria
+define void @test2(i1 %cnd, i64 addrspace(1)* %base_obj, i64 addrspace(1)* %base_arg2)  gc "statepoint-example" {
+; CHECK-LABEL: @test2
+entry:
+  %obj = getelementptr i64, i64 addrspace(1)* %base_obj, i32 1
+  br label %loop
+
+loop:                                             ; preds = %loop, %entry
+; CHECK-LABEL: loop
+; CHECK:   %base_phi = phi i64 addrspace(1)*
+; CHECK-DAG: [ %base_obj, %entry ]
+; CHECK-DAG: [ %base_select
+; CHECK-NOT: base_phi2
+; CHECK: next = select
+; CHECK: base_select
+; CHECK: extra2 = select
+; CHECK: base_select
+; CHECK: statepoint
+;; Both 'next' and 'extra2' are live across the backedge safepoint...
+  %current = phi i64 addrspace(1)* [ %obj, %entry ], [ %next, %loop ]
+  %extra = phi i64 addrspace(1)* [ %obj, %entry ], [ %extra2, %loop ]
+  %nexta = getelementptr i64, i64 addrspace(1)* %current, i32 1
+  %next = select i1 %cnd, i64 addrspace(1)* %nexta, i64 addrspace(1)* %base_arg2
+  %extra2 = select i1 %cnd, i64 addrspace(1)* %nexta, i64 addrspace(1)* %base_arg2
+  %safepoint_token = call i32 (void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(void ()* @foo, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0)
+  br label %loop
+}
+
+declare void @foo()
+declare i32 @llvm.experimental.gc.statepoint.p0f_isVoidf(void ()*, i32, i32, ...)
+declare i32 @llvm.experimental.gc.statepoint.p0f_isVoidp1i64f(void (i64 addrspace(1)*)*, i32, i32, ...)