[PATCH] D35294: [CGP] Allow cycles during Phi traversal in OptimizaMemoryInst

[Serguei Katkov via Phabricator via llvm-commits]

skatkov updated this revision to Diff 107023.
skatkov added a comment.

Please take a look.


https://reviews.llvm.org/D35294

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll


Index: test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
===================================================================
--- test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
+++ test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
@@ -194,7 +194,6 @@
   br label %fallthrough
 }
 
-
 declare void @slowpath(i32, i32*)
 
 ; Make sure we don't end up in an infinite loop after we fail to sink.
@@ -218,3 +217,37 @@
 pl_loop.i.i122:
   br label %pl_loop.i.i122
 }
+
+; Make sure we can sink address computation even
+; if there is a cycle in phi nodes.
+define void @test9(i1 %cond, i64* %base) {
+; CHECK-LABEL: @test9
+entry:
+  %addr = getelementptr inbounds i64, i64* %base, i64 5
+  %casted = bitcast i64* %addr to i32*
+  br label %header
+
+header:
+  %iv = phi i32 [0, %entry], [%iv.inc, %backedge]
+  %casted.loop = phi i32* [%casted, %entry], [%casted.merged, %backedge]
+  br i1 %cond, label %if.then, label %backedge
+
+if.then:
+  call void @foo(i32 %iv)
+  %addr.1 = getelementptr inbounds i64, i64* %base, i64 5
+  %casted.1 = bitcast i64* %addr.1 to i32*
+  br label %backedge
+
+backedge:
+; CHECK-LABEL: backedge:
+; CHECK: getelementptr i8, {{.+}} 40
+  %casted.merged = phi i32* [%casted.loop, %header], [%casted.1, %if.then]
+  %v = load i32, i32* %casted.merged, align 4
+  call void @foo(i32 %v)
+  %iv.inc = add i32 %iv, 1
+  %cmp = icmp slt i32 %iv.inc, 1000
+  br i1 %cmp, label %header, label %exit
+
+exit:
+  ret void
+}
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -4278,11 +4278,17 @@
     Value *V = worklist.back();
     worklist.pop_back();
 
-    // Break use-def graph loops.
-    if (!Visited.insert(V).second) {
-      AddrModeFound = false;
-      break;
-    }
+    // We allow traversing the cyclic Phi nodes.
+    // In case of success after this loop we ensure that traversing through
+    // Phi nodes ends up with all cases to compute address of the form
+    //    BaseGV + Base + Scale * Index + Offset
+    // where Scale and Offset are constans and BaseGV, Base and Index
+    // are exactly the same Values in all cases.
+    // It means that BaseGV, Scale and Offset dominate our memory instruction
+    // and have the same value as they had in address computation represented
+    // as Phi. So we can safely sink address computation to memory instruction.
+    if (!Visited.insert(V).second)
+      continue;
 
     // For a PHI node, push all of its incoming values.
     if (PHINode *P = dyn_cast<PHINode>(V)) {


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