[PATCH] D24980: [GlobalOpt]: See if it's possible to shrink Stores with Undef during global variable initialization to eliminate constructor functions

[Aditya Nandakumar via llvm-commits]

aditya_nandakumar removed rL LLVM as the repository for this revision.
aditya_nandakumar updated this revision to Diff 73857.
aditya_nandakumar added a comment.

Thanks David.

Updated based on your comments + Clang Formatted.


https://reviews.llvm.org/D24980

Files:
  lib/Transforms/Utils/Evaluator.cpp
  test/Transforms/GlobalOpt/ShrinkUndefStore.ll


Index: test/Transforms/GlobalOpt/ShrinkUndefStore.ll
===================================================================
--- /dev/null
+++ test/Transforms/GlobalOpt/ShrinkUndefStore.ll
@@ -0,0 +1,32 @@
+; RUN: opt -globalopt -S < %s | FileCheck %s
+ at _ZL9aPosition = internal addrspace(2) global [1 x <3 x float>] zeroinitializer, align 16
+ at llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__ctor1, i8* null }]
+; CHECK-NOT: ctor1
+; CHECK: constant [1 x <3 x float>] [<3 x float> <float 4.000000e+00, float 4.000000e+00, float 4.000000e+00>]
+; CHECK-LABEL: Z4aFooi
+
+; Function Attrs: nounwind optsize
+define <3 x float> @_Z4aFooi(i32 %i) {
+entry:
+  %idxprom = sext i32 %i to i64
+  %arrayidx = getelementptr inbounds [1 x <3 x float>], [1 x <3 x float>] addrspace(2)* @_ZL9aPosition, i32 0, i64 %idxprom
+  %castToVec4 = bitcast <3 x float> addrspace(2)* %arrayidx to <4 x float> addrspace(2)*
+  %loadVec4 = load <4 x float>, <4 x float> addrspace(2)* %castToVec4
+  %extractVec = shufflevector <4 x float> %loadVec4, <4 x float> undef, <3 x i32> <i32 0, i32 1, i32 2>
+  ret <3 x float> %extractVec
+}
+
+; Function Attrs: nounwind optsize
+define internal fastcc void @__cxx_global_var_init() {
+entry:
+  %arrayidx = getelementptr inbounds [1 x <3 x float>], [1 x <3 x float>] addrspace(2)* @_ZL9aPosition, i32 0, i64 0
+  store <4 x float> <float 4.000000e+00, float 4.000000e+00, float 4.000000e+00, float undef>, <4 x float> addrspace(2)* bitcast ([1 x <3 x float>] addrspace(2)* @_ZL9aPosition to <4 x float> addrspace(2)*)
+  ret void
+}
+
+; Function Attrs: nounwind optsize
+define internal void @_GLOBAL__ctor1() {
+entry:
+  call fastcc void @__cxx_global_var_init()
+  ret void
+}
Index: lib/Transforms/Utils/Evaluator.cpp
===================================================================
--- lib/Transforms/Utils/Evaluator.cpp
+++ lib/Transforms/Utils/Evaluator.cpp
@@ -247,13 +247,51 @@
               IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
               Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
               Constant * const IdxList[] = {IdxZero, IdxZero};
-
               Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
               if (auto *FoldedPtr = ConstantFoldConstant(Ptr, DL, TLI))
                 Ptr = FoldedPtr;
-
-            // If we can't improve the situation by introspecting NewTy,
-            // we have to give up.
+            } else if (auto *ATy = dyn_cast<ArrayType>(NewTy)) {
+              // See if we can remove undefs at the end of a vector to make
+              // the types compatible.
+              // For eg.
+              // @globalvariable1 = internal global [1 x <3 x float>]
+              // zeroinitializer
+              // store <4 x float> <float 4.000000e+00, float 4.000000e+00,
+              // float 4.000000e+00, float undef>,
+              // <4 x float> * bitcast ([1 x <3 x float>] * @globalvariable1 to
+              // <4 x float> *)
+              auto *ElemTy = dyn_cast<VectorType>(ATy->getElementType());
+              auto *Vec = dyn_cast<ConstantVector>(Val);
+              if (Vec && ElemTy) {
+                // See if the Constant vector has undefs at the end
+                // and can be truncated to ElemTy's size.
+                unsigned ValSize = Vec->getNumOperands();
+                // Make sure we're truncating and not extending.
+                if (ValSize <= ElemTy->getNumElements())
+                  return false;
+                for (unsigned i = ElemTy->getNumElements(); i < ValSize; ++i) {
+                  Value *V = Vec->getOperand(i);
+                  if (!isa<UndefValue>(V))
+                    // This is not an undef and we can't shrink the store.
+                    return false;
+                }
+                // We know we can shrink it to ElemTy's size without losing
+                // data.
+                SmallVector<Constant *, 4> NewVec;
+                for (unsigned i = 0; i < ElemTy->getNumElements(); ++i)
+                  NewVec.push_back(Vec->getOperand(i));
+                Val = ConstantVector::get(NewVec);
+                IntegerType *IdxTy = IntegerType::get(Val->getContext(), 32);
+                Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
+                Constant *const IdxList[] = {IdxZero, IdxZero};
+                Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
+                NewTy = ElemTy;
+              } else {
+
+                DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
+                                "evaluate.\n");
+                return false;
+              }
             } else {
               DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
                     "evaluate.\n");


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