[FastISel][SelectionDAG]Teach fastISel about GC intrinsics

[anna]

Summary

We are crashing in LLC at O0 when gc intrinsics are present in the block.
The reason being FastISel performs basic block ISel by modifying GC.relocates
to be the first instruction in the block. This can cause us to visit the GC
relocate before it's corresponding GC.statepoint is visited, which is incorrect.
When we lower the statepoint, we record the base and derived pointers, along
with the gc.relocates. After this we can visit the gc.relocate.

This patch avoids fastISel from incorrectly creating the block with gc.relocate
as the first instruction.

[skatkov]

LGTM

[anna]

ping

[anna]

ping2.

[skatkov]

Still LGTM :)

[anna]

I'm going ahead and accepting the revision based on @skatkov 's LGTM above (and haven't heard any comments from other reviewers). If there's some future comments, I'll address it in post commit review. Thanks.

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

if (FastIS) {
             BI = std::next(BasicBlock::const_iterator(BeforeInst));
             --NumFastIselRemaining;
             ++NumFastIselSuccess;
           }
           continue;
         }
 
         // Then handle certain instructions as single-LLVM-Instruction blocks.
-        if (isa<CallInst>(Inst)) {
+        // We cannot separate out GCrelocates to their own blocks since we need
+        // to keep track of gc-relocates for a particular gc-statepoint. This is
+        // done by SelectionDAGBuilder::LowerAsSTATEPOINT, called before
+        // visitGCRelocate.
+        if (isa<CallInst>(Inst) && !isStatepoint(Inst) && !isGCRelocate(Inst)) {
           OptimizationRemarkMissed R("sdagisel", "FastISelFailure",
                                      Inst->getDebugLoc(), LLVMBB);
 
           R << "FastISel missed call";
 
           if (R.isEnabled() || EnableFastISelAbort) {
             std::string InstStrStorage;
             raw_string_ostream InstStr(InstStrStorage);

test/CodeGen/Generic/fast-isel-gc-intrinsics.ll

+; RUN: llc < %s -fast-isel
+
+; Dont crash with gc intrinsics.
+
+; gcrelocate call should not be an LLVM Machine Block by itself.
+define i8 addrspace(1)* @test_gcrelocate(i8 addrspace(1)* %v) gc "statepoint-example" {
+entry:
+  %tok = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %v)
+  %vnew = call i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %tok,  i32 7, i32 7)
+  ret i8 addrspace(1)* %vnew
+}
+
+; gcresult calls are fine in their own blocks.
+define i1 @test_gcresult() gc "statepoint-example" {
+entry:
+  %safepoint_token = tail call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0)
+  %call1 = call zeroext i1 @llvm.experimental.gc.result.i1(token %safepoint_token)
+  ret i1 %call1
+}
+
+; we are okay here because we see the gcrelocate and avoid generating their own
+; block.
+define i1 @test_gcresult_gcrelocate(i8 addrspace(1)* %v) gc "statepoint-example" {
+entry:
+  %safepoint_token = tail call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %v)
+  %call1 = call zeroext i1 @llvm.experimental.gc.result.i1(token %safepoint_token)
+  %vnew = call i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %safepoint_token,  i32 7, i32 7)
+  ret i1 %call1
+}
+
+define i8 addrspace(1)*  @test_non_entry_block(i8 addrspace(1)* %v, i8 %val) gc "statepoint-example" {
+entry:
+ %load = load i8, i8 addrspace(1)* %v
+ %cmp = icmp eq i8 %load, %val
+ br i1 %cmp, label %func_call, label %exit
+
+func_call:
+ call void @dummy()
+ %tok = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %v)
+ %vnew = call i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %tok,  i32 7, i32 7)
+ ret i8 addrspace(1)* %vnew
+
+exit:
+  ret i8 addrspace(1)* %v
+
+}
+
+declare void @dummy()
+declare void @foo()
+
+declare zeroext i1 @return_i1()
+declare token @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...)
+declare token @llvm.experimental.gc.statepoint.p0f_i1f(i64, i32, i1 ()*, i32, i32, ...)
+declare i1 @llvm.experimental.gc.result.i1(token)
+declare i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token, i32, i32)