[PATCH] D14699: [GlobalOpt] Allow constant globals to be SRA'd

[James Molloy via llvm-commits]

jmolloy created this revision.
jmolloy added reviewers: hfinkel, joker.eph, dexonsmith.
jmolloy added a subscriber: llvm-commits.
jmolloy set the repository for this revision to rL LLVM.

The current logic assumes that any constant global will never be SRA'd. I presume this is because normally constant globals can be pushed into their uses and deleted. However, that sometimes can't happen (which is where you really want SRA, so the elements that can be eliminated, are!).

There seems to be no reason why we can't SRA constants too, so let's do it.

Repository:
  rL LLVM

http://reviews.llvm.org/D14699

Files:
  lib/Transforms/IPO/GlobalOpt.cpp
  test/Transforms/GlobalOpt/globalsra.ll

Index: test/Transforms/GlobalOpt/globalsra.ll
===================================================================
--- test/Transforms/GlobalOpt/globalsra.ll
+++ test/Transforms/GlobalOpt/globalsra.ll
@@ -22,3 +22,24 @@
         ret double %X
 }
 
+ at G2 = internal constant { i32, float, { double } } {
+    i32 1, 
+    float 1.000000e+00, 
+    { double } { double 1.727000e+01 } }                ; <{ i32, float, { double } }*> [#uses=3]
+
+define void @onlystore2() {
+        store i32 123, i32* getelementptr ({ i32, float, { double } }, { i32, float, { double } }* @G2, i32 0, i32 0)
+        ret void
+}
+
+define float @storeinit2() {
+        store float 1.000000e+00, float* getelementptr ({ i32, float, { double } }, { i32, float, { double } }* @G2, i32 0, i32 1)
+        %X = load float, float* getelementptr ({ i32, float, { double } }, { i32, float, { double } }* @G2, i32 0, i32 1)           ; <float> [#uses=1]
+        ret float %X
+}
+
+define double @constantize2() {
+        %X = load double, double* getelementptr ({ i32, float, { double } }, { i32, float, { double } }* @G2, i32 0, i32 2, i32 0)           ; <double> [#uses=1]
+        ret double %X
+}
+
Index: lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- lib/Transforms/IPO/GlobalOpt.cpp
+++ lib/Transforms/IPO/GlobalOpt.cpp
@@ -475,7 +475,7 @@
   if (!GlobalUsersSafeToSRA(GV))
     return nullptr;
 
-  assert(GV->hasLocalLinkage() && !GV->isConstant());
+  assert(GV->hasLocalLinkage());
   Constant *Init = GV->getInitializer();
   Type *Ty = Init->getType();
 
@@ -1846,7 +1846,8 @@
     }
     return Changed;
 
-  } else if (GS.StoredType <= GlobalStatus::InitializerStored) {
+  }
+  if (GS.StoredType <= GlobalStatus::InitializerStored) {
     DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
     GV->setConstant(true);
 
@@ -1859,17 +1860,20 @@
             << "all users and delete global!\n");
       GV->eraseFromParent();
       ++NumDeleted;
+      return true;
     }
 
+    // Fall through to the next check; see if we can optimize further.
     ++NumMarked;
-    return true;
-  } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
+  }
+  if (!GV->getInitializer()->getType()->isSingleValueType()) {
     const DataLayout &DL = GV->getParent()->getDataLayout();
     if (GlobalVariable *FirstNewGV = SRAGlobal(GV, DL)) {
       GVI = FirstNewGV->getIterator(); // Don't skip the newly produced globals!
       return true;
     }
-  } else if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
+  }
+  if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
     // If the initial value for the global was an undef value, and if only
     // one other value was stored into it, we can just change the
     // initializer to be the stored value, then delete all stores to the


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