[PATCH] D75598: [InstCombine] Handle gc.relocate(null) in one iteration

[Serguei Katkov via Phabricator via llvm-commits]

skatkov updated this revision to Diff 285004.
skatkov edited the summary of this revision.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75598/new/

https://reviews.llvm.org/D75598

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/statepoint-iter.ll


Index: llvm/test/Transforms/InstCombine/statepoint-iter.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/statepoint-iter.ll
@@ -0,0 +1,56 @@
+; RUN: opt < %s -instcombine -instcombine-max-iterations=1 -S | FileCheck %s
+; These tests check the optimizations specific to
+; pointers being relocated at a statepoint.
+
+
+declare void @func()
+
+define i1 @test_null(i1 %cond) gc "statepoint-example" {
+entry:
+  br i1 %cond, label %left, label %right
+
+right:
+  br label %merge
+
+left:
+  %safepoint_token = tail call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0, i32* null)
+  %pnew = call i32* @llvm.experimental.gc.relocate.p1i32(token %safepoint_token,  i32 7, i32 7)
+  br label %merge
+
+merge:
+  %pnew_phi = phi i32* [null, %right], [%pnew, %left]
+  %safepoint_token2 = tail call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0, i32* %pnew_phi)
+  %pnew2 = call i32* @llvm.experimental.gc.relocate.p1i32(token %safepoint_token2,  i32 7, i32 7)
+  %cmp = icmp eq i32* %pnew2, null
+  ret i1 %cmp
+; CHECK-LABEL: test_null
+; CHECK-NOT: %pnew
+; CHECK-NOT: %pnew2
+; CHECK: ret i1 true
+}
+
+define i32* @test_undef(i1 %cond) gc "statepoint-example" {
+entry:
+  br i1 %cond, label %left, label %right
+
+right:
+  br label %merge
+
+left:
+  %safepoint_token = tail call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0, i32* undef)
+  %pnew = call i32* @llvm.experimental.gc.relocate.p1i32(token %safepoint_token,  i32 7, i32 7)
+  br label %merge
+
+merge:
+  %pnew_phi = phi i32* [undef, %right], [%pnew, %left]
+  %safepoint_token2 = tail call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0, i32* %pnew_phi)
+  %pnew2 = call i32* @llvm.experimental.gc.relocate.p1i32(token %safepoint_token2,  i32 7, i32 7)
+  ret i32* %pnew2
+; CHECK-LABEL: test_undef
+; CHECK-NOT: %pnew
+; CHECK-NOT: %pnew2
+; CHECK: ret i32* undef
+}
+
+declare token @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...)
+declare i32* @llvm.experimental.gc.relocate.p1i32(token, i32, i32)
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1474,6 +1474,27 @@
     AC.updateAffectedValues(II);
     break;
   }
+  case Intrinsic::experimental_gc_statepoint: {
+    auto &GCSP = *cast<GCStatepointInst>(II);
+    // Let's we have the following case:
+    // A = gc.relocate(null)
+    // B = statepoint(A)
+    // C = gc.relocate(A)
+    // A will be substituted with null and its user B will be added to worklist.
+    // Statepoint B is not simplified and if C was considered before it will be
+    // re-considered after simplification of A.
+    // To resolve this case while processing statepoint B we add all gc.relocate
+    // users to worklist to give a chance to be simplified to null.
+    // This is to reduce the number of InstCombine iteration.
+    // Actually C can be transformed on the next iteration.
+    // chains in one iteration.
+    // TODO: we can handle relocation here, it will reduce the number of
+    // relocations to re-consider and also helps to reduce the number of
+    // gc live pointers in statepoint instruction bundle.
+    for (const GCRelocateInst *Reloc : GCSP.getGCRelocates())
+      Worklist.add(const_cast<GCRelocateInst *>(Reloc));
+    break;
+  }
   case Intrinsic::experimental_gc_relocate: {
     auto &GCR = *cast<GCRelocateInst>(II);
 


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