Add a pass for constructing gc.statepoint sequences w/explicit relocations

This patch consists of a single pass whose only purpose is to visit previous inserted gc.statepoints which do not have gc.relocates inserted yet, and insert them. This can be used either immediately after IR generation to perform 'early safepoint insertion' or late in the pass order to perform 'late insertion'.

This patch is setting the stage for work to continue in tree.  In particular, there are known naming and style violations in the current patch.  I'll try to get those resolved over the next week or so.  As I touch each area to make style changes, I need to make sure we have adequate testing in place.  As part of the cleanup, I will be cleaning up a collection of test cases we have out of tree and submitting them upstream. The tests included in this change are very basic and mostly to provide examples of usage.

The pass has several main subproblems it needs to address:
- First, it has identify any live pointers. In the current code, the use of address spaces to distinguish pointers to GC managed objects is hard coded, but this will become parametrizable in the near future.  Note that the current change doesn't actually contain a useful liveness analysis.  It was seperated into a followup change as the code wasn't ready to be shared.  Instead, the current implementation just considers any dominating def of appropriate pointer type to be live.
- Second, it has to identify base pointers for each live pointer. This is a fairly straight forward data flow algorithm. 
- Third, the information in the previous steps is used to actually introduce rewrites. Rather than trying to do this by hand, we simply re-purpose the code behind Mem2Reg to do this for us.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229945 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/InitializePasses.h

@@ -239,6 +239,7 @@ void initializeRegionOnlyPrinterPass(PassRegistry&);
 void initializeRegionOnlyViewerPass(PassRegistry&);
 void initializeRegionPrinterPass(PassRegistry&);
 void initializeRegionViewerPass(PassRegistry&);
+void initializeRewriteStatepointsForGCPass(PassRegistry&);
 void initializeSCCPPass(PassRegistry&);
 void initializeSROAPass(PassRegistry&);
 void initializeSROA_DTPass(PassRegistry&);

include/llvm/Transforms/Scalar.h

@@ -433,6 +433,13 @@ FunctionPass *createStraightLineStrengthReducePass();
 //
 ModulePass *createPlaceSafepointsPass();
 
+//===----------------------------------------------------------------------===//
+//
+// RewriteStatepointsForGC - Rewrite any gc.statepoints which do not yet have
+// explicit relocations to include explicit relocations.
+//
+FunctionPass *createRewriteStatepointsForGCPass();
+
 } // End llvm namespace
 
 #endif

lib/Transforms/Scalar/CMakeLists.txt

@@ -31,6 +31,7 @@ add_llvm_library(LLVMScalarOpts
   PlaceSafepoints.cpp
   Reassociate.cpp
   Reg2Mem.cpp
+  RewriteStatepointsForGC.cpp
   SCCP.cpp
   SROA.cpp
   SampleProfile.cpp

lib/Transforms/Scalar/Scalar.cpp

@@ -61,6 +61,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializePartiallyInlineLibCallsPass(Registry);
   initializeReassociatePass(Registry);
   initializeRegToMemPass(Registry);
+  initializeRewriteStatepointsForGCPass(Registry);
   initializeSCCPPass(Registry);
   initializeIPSCCPPass(Registry);
   initializeSROAPass(Registry);

test/Transforms/RewriteStatepointsForGC/basics.ll

@@ -0,0 +1,77 @@
+; This is a collection of really basic tests for gc.statepoint rewriting.
+; RUN:  opt %s -rewrite-statepoints-for-gc -S | FileCheck %s
+
+declare void @foo()
+
+; Trivial relocation over a single call
+define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj) {
+; CHECK-LABEL: @test1
+; CHECK-LABEL: entry:
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %obj.relocated = call coldcc i8 addrspace(1)*
+entry:
+  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)
+  ret i8 addrspace(1)* %obj
+}
+
+; Two safepoints in a row (i.e. consistent liveness)
+define i8 addrspace(1)* @test2(i8 addrspace(1)* %obj) {
+; CHECK-LABEL: @test2
+; CHECK-LABEL: entry:
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %obj.relocated = call coldcc i8 addrspace(1)*
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %obj.relocated1 = call coldcc i8 addrspace(1)*
+entry:
+  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)
+  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)
+  ret i8 addrspace(1)* %obj
+}
+
+; A simple derived pointer
+define i8 @test3(i8 addrspace(1)* %obj) {
+; CHECK-LABEL: entry:
+; CHECK-NEXT: getelementptr
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %derived.relocated = call coldcc i8 addrspace(1)*
+; CHECK-NEXT: %obj.relocated = call coldcc i8 addrspace(1)*
+; CHECK-NEXT: load i8 addrspace(1)* %derived.relocated
+; CHECK-NEXT: load i8 addrspace(1)* %obj.relocated
+entry:
+  %derived = getelementptr i8 addrspace(1)* %obj, i64 10
+  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)
+
+  %a = load i8 addrspace(1)* %derived
+  %b = load i8 addrspace(1)* %obj
+  %c = sub i8 %a, %b
+  ret i8 %c
+}
+
+; Tests to make sure we visit both the taken and untaken predeccessor 
+; of merge.  This was a bug in the dataflow liveness at one point.
+define i8 addrspace(1)* @test4(i1 %cmp, i8 addrspace(1)* %obj) {
+entry:
+  br i1 %cmp, label %taken, label %untaken
+
+taken:
+; CHECK-LABEL: taken:
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %obj.relocated = call coldcc i8 addrspace(1)*
+  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 %merge
+
+untaken:
+; CHECK-LABEL: untaken:
+; CHECK-NEXT: gc.statepoint
+; CHECK-NEXT: %obj.relocated1 = call coldcc i8 addrspace(1)*
+  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 %merge
+
+merge:
+; CHECK-LABEL: merge:
+; CHECK-NEXT: %.0 = phi i8 addrspace(1)* [ %obj.relocated, %taken ], [ %obj.relocated1, %untaken ]
+; CHECK-NEXT: ret i8 addrspace(1)* %.0
+  ret i8 addrspace(1)* %obj
+}
+
+declare i32 @llvm.experimental.gc.statepoint.p0f_isVoidf(void ()*, i32, i32, ...)