[PATCH] D42549: [CodeGen] Use the zero initializer instead of storing an all zero representation.

[Matt Davis via Phabricator via cfe-commits]

mattd updated this revision to Diff 133540.
mattd added a comment.

Thanks for the test tips.  I realize the original was a bit carried away,  my apologies for that.  This updated test visits the same code path that we're trying to test, and is much more concise.


https://reviews.llvm.org/D42549

Files:
  lib/CodeGen/CGExprConstant.cpp
  test/CodeGen/array-init.c


Index: test/CodeGen/array-init.c
===================================================================
--- test/CodeGen/array-init.c
+++ test/CodeGen/array-init.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 %s -O0 -triple x86_64-unknown-linux-gnu -emit-llvm -o - | FileCheck %s
+
+// CHECK: @{{.*}}.a1 = internal constant [5 x i32] [i32 0, i32 1, i32 2, i32 0, i32 0]
+// CHECK: @{{.*}}.a2 = internal constant [5 x i32] zeroinitializer
+// CHECK: @{{.*}}.a3 = internal constant [5 x i32] zeroinitializer
+
+void testConstArrayInits(void)
+{
+  const int a1[5] = {0,1,2};
+  const int a2[5] = {0,0,0};
+  const int a3[5] = {0};
+}
Index: lib/CodeGen/CGExprConstant.cpp
===================================================================
--- lib/CodeGen/CGExprConstant.cpp
+++ lib/CodeGen/CGExprConstant.cpp
@@ -859,9 +859,10 @@
 
     // Copy initializer elements.
     SmallVector<llvm::Constant*, 16> Elts;
-    Elts.reserve(NumInitableElts + NumElements);
+    Elts.reserve(std::max(NumInitableElts, NumElements));
 
     bool RewriteType = false;
+    bool AllNullValues = true;
     for (unsigned i = 0; i < NumInitableElts; ++i) {
       Expr *Init = ILE->getInit(i);
       llvm::Constant *C = Emitter.tryEmitPrivateForMemory(Init, EltType);
@@ -869,8 +870,15 @@
         return nullptr;
       RewriteType |= (C->getType() != ElemTy);
       Elts.push_back(C);
+      if (AllNullValues && !C->isNullValue())
+        AllNullValues = false;
     }
 
+    // If all initializer elements are "zero," then avoid storing NumElements
+    // instances of the zero representation.
+    if (AllNullValues)
+      return llvm::ConstantAggregateZero::get(AType);
+
     RewriteType |= (fillC->getType() != ElemTy);
     Elts.resize(NumElements, fillC);
 
@@ -877,7 +885,7 @@
     if (RewriteType) {
       // FIXME: Try to avoid packing the array
       std::vector<llvm::Type*> Types;
-      Types.reserve(NumInitableElts + NumElements);
+      Types.reserve(Elts.size());
       for (unsigned i = 0, e = Elts.size(); i < e; ++i)
         Types.push_back(Elts[i]->getType());
       llvm::StructType *SType = llvm::StructType::get(AType->getContext(),


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