[PATCH] D25502: [SimplifyCFG] Don't create PHI nodes for constant bundle operands

[Sanjoy Das via llvm-commits]

sanjoy created this revision.
sanjoy added a reviewer: jmolloy.
sanjoy added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

Constant bundle operands may need to retain their constant-ness for
correctness.  I'll admit that this is slightly odd, but it looks like
SimplifyCFG already does this for things like @llvm.frameaddress and
@llvm.stackmap, so I suppose adding one more case is not a big deal.

It is possible to add a mechanism to denote bundle operands that need to
remain constants, but that's probably too complicated for the time
being.


https://reviews.llvm.org/D25502

Files:
  include/llvm/IR/CallSite.h
  include/llvm/IR/InstrTypes.h
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/sink-common-code.ll


Index: test/Transforms/SimplifyCFG/sink-common-code.ll
===================================================================
--- test/Transforms/SimplifyCFG/sink-common-code.ll
+++ test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -755,6 +755,32 @@
 ; CHECK-NOT: exact
 ; CHECK: }
 
+declare i32 @call_target()
+
+define void @test_operand_bundles(i1 %cond, i32* %ptr) {
+entry:
+  br i1 %cond, label %left, label %right
+
+left:
+  %val0 = call i32 @call_target() [ "deopt"(i32 10) ]
+  store i32 %val0, i32* %ptr
+  br label %merge
+
+right:
+  %val1 = call i32 @call_target() [ "deopt"(i32 20) ]
+  store i32 %val1, i32* %ptr
+  br label %merge
+
+merge:
+  ret void
+}
+
+; CHECK-LABEL: @test_operand_bundles(
+; CHECK: left:
+; CHECK-NEXT:   %val0 = call i32 @call_target() [ "deopt"(i32 10) ]
+; CHECK: right:
+; CHECK-NEXT:   %val1 = call i32 @call_target() [ "deopt"(i32 20) ]
+
 ; CHECK: !0 = !{!1, !1, i64 0}
 ; CHECK: !1 = !{!"float", !2}
 ; CHECK: !2 = !{!"an example type tree"}
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1362,7 +1362,14 @@
     // FIXME: many arithmetic intrinsics have no issue taking a
     // variable, however it's hard to distingish these from
     // specials such as @llvm.frameaddress that require a constant.
-    return !isa<IntrinsicInst>(I);
+    if (isa<IntrinsicInst>(I))
+      return false;
+
+    if (ImmutableCallSite(I).isBundleOperand(OpIdx))
+      return false;
+
+    return true;
+
   case Instruction::ShuffleVector:
     // Shufflevector masks are constant.
     return OpIdx != 2;
Index: include/llvm/IR/InstrTypes.h
===================================================================
--- include/llvm/IR/InstrTypes.h
+++ include/llvm/IR/InstrTypes.h
@@ -1337,6 +1337,12 @@
     return bundle_op_info_end()[-1].End;
   }
 
+  /// Return true if the operand at index \p Idx is a bundle operand.
+  bool isBundleOperand(unsigned Idx) const {
+    return hasOperandBundles() && Idx >= getBundleOperandsStartIndex() &&
+           Idx < getBundleOperandsEndIndex();
+  }
+
   /// \brief Return the total number operands (not operand bundles) used by
   /// every operand bundle in this OperandBundleUser.
   unsigned getNumTotalBundleOperands() const {
Index: include/llvm/IR/CallSite.h
===================================================================
--- include/llvm/IR/CallSite.h
+++ include/llvm/IR/CallSite.h
@@ -512,6 +512,10 @@
     CALLSITE_DELEGATE_GETTER(countOperandBundlesOfType(ID));
   }
 
+  bool isBundleOperand(unsigned Idx) const {
+    CALLSITE_DELEGATE_GETTER(isBundleOperand(Idx));
+  }
+
   IterTy arg_begin() const {
     CALLSITE_DELEGATE_GETTER(arg_begin());
   }


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