[llvm-commits] [llvm] r153576 - in /llvm/trunk: lib/Transforms/IPO/GlobalOpt.cpp test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll

[Benjamin Kramer]

Author: d0k
Date: Wed Mar 28 09:50:09 2012
New Revision: 153576

URL: http://llvm.org/viewvc/llvm-project?rev=153576&view=rev
Log:
GlobalOpt: If we have an inbounds GEP from a ConstantAggregateZero global that we just determined to be constant, replace all loads from it with a zero value.

Added:
    llvm/trunk/test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll
Modified:
    llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp

Modified: llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp?rev=153576&r1=153575&r2=153576&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp Wed Mar 28 09:50:09 2012
@@ -341,6 +341,12 @@
           dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
         if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
           SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
+
+        // If the initializer is an all-null value and we have an inbounds GEP,
+        // we already know what the result of any load from that GEP is.
+        // TODO: Handle splats.
+        if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
+          SubInit = Constant::getNullValue(GEP->getType()->getElementType());
       }
       Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
 

Added: llvm/trunk/test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll?rev=153576&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll (added)
+++ llvm/trunk/test/Transforms/GlobalOpt/zeroinitializer-gep-load.ll Wed Mar 28 09:50:09 2012
@@ -0,0 +1,11 @@
+; RUN: opt < %s -S -globalopt | FileCheck %s
+
+ at zero = internal global [10 x i32] zeroinitializer
+
+define i32 @test1(i64 %idx) nounwind {
+  %arrayidx = getelementptr inbounds [10 x i32]* @zero, i64 0, i64 %idx
+  %l = load i32* %arrayidx
+  ret i32 %l
+; CHECK: @test1
+; CHECK: ret i32 0
+}