[PlaceSafepoints] Assertion on that gc_result can not have preceding phis should only apply to invoke statepoint

[• chenli]

Summary

When PlaceSafepoints pass replaces old return result with gc_result from statepoint, it asserts that gc_result can not have preceding phis in its parent block. This is only true on invoke statepoint, which terminates the block and puts its result at the beginning of the normal successor block. Call statepoint does not terminate the block and thus its result is in the same block with it. There should be no restriction on whether there are phis or not.

[igor-laevsky]

lgtm

lib/Transforms/Scalar/PlaceSafepoints.cpp

bool PlaceSafepoints::runOnFunction(Function &F) {
   }
   assert(Results.size() == ParsePointNeeded.size());
 
   // Adjust all users of the old call sites to use the new ones instead
   for (size_t i = 0; i < ParsePointNeeded.size(); i++) {
     CallSite &CS = ParsePointNeeded[i];
     Value *GCResult = Results[i];
     if (GCResult) {
-      // Can not RAUW for the gc result in case of phi nodes preset.
-      assert(!isa<PHINode>(cast<Instruction>(GCResult)->getParent()->begin()));
+      // Can not RAUW for the invoke gc result in case of phi nodes preset.
+      assert(CS.isCall() || !isa<PHINode>(cast<Instruction>(GCResult)->getParent()->begin()));
 
       // Replace all uses with the new call
       CS.getInstruction()->replaceAllUsesWith(GCResult);
     }
 
     // Now that we've handled all uses, remove the original call itself
     // Note: The insert point can't be the deleted instruction!
     CS.getInstruction()->eraseFromParent();

test/Transforms/PlaceSafepoints/call_gc_result.ll

+;; RUN: opt %s -place-safepoints -S | FileCheck %s
+
+;; This test is to verify that gc_result from a call statepoint
+;; can have preceding phis in its parent basic block. Unlike
+;; invoke statepoint, call statepoint does not terminate the
+;; block, and thus its gc_result is in the same block with the
+;; call statepoint.
+
+declare i32 @foo()
+
+define i32 @test1(i1 %cond, i32 %a) gc "statepoint-example" {
+entry:
+  br i1 %cond, label %branch1, label %branch2
+  
+branch1:
+  %b = add i32 %a, 1
+  br label %merge
+ 
+branch2:
+  br label %merge
+
+merge:
+;; CHECK:     %phi = phi i32 [ %a, %branch2 ], [ %b, %branch1 ]
+;; CHECK-NEXT:  %safepoint_token.1 = call i32 (i64, i32, i32 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i32f(i64 2882400000, i32 0, i32 ()* @foo, i32 0, i32 0, i32 0, i32 0)
+;; CHECK-NEXT:  %ret.2 = call i32 @llvm.experimental.gc.result.i32(i32 %safepoint_token.1)
+  %phi = phi i32 [ %a, %branch2 ], [ %b, %branch1 ]
+  %ret = call i32 @foo()
+  ret i32 %ret
+}
+
+; This function is inlined when inserting a poll.
+declare void @do_safepoint()
+define void @gc.safepoint_poll() {
+; CHECK-LABEL: gc.safepoint_poll
+entry:
+  call void @do_safepoint()
+  ret void
+}