DAGCombiner: fix use-counting issue when forming zextload

DAGCombiner was counting all uses of a load node  when considering whether it's
worth combining into a zextload. Really, it wants to ignore the chain and just
count real uses.

rdar://problem/13896307

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185419 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 00469b0f32aa198894b54d067166bd5c4fdfeaec..1688fc495ad9d71ba86a058f77ef6aa074095487 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2755,7 +2755,7 @@ SDValue DAGCombiner::visitAND(SDNode *N) {
       ? cast<LoadSDNode>(N0.getOperand(0))
       : cast<LoadSDNode>(N0);
     if (LN0->getExtensionType() != ISD::SEXTLOAD &&
-        LN0->isUnindexed() && N0.hasOneUse() && LN0->hasOneUse()) {
+        LN0->isUnindexed() && N0.hasOneUse() && SDValue(LN0, 0).hasOneUse()) {
       uint32_t ActiveBits = N1C->getAPIntValue().getActiveBits();
       if (ActiveBits > 0 && APIntOps::isMask(ActiveBits, N1C->getAPIntValue())){
         EVT ExtVT = EVT::getIntegerVT(*DAG.getContext(), ActiveBits);

diff --git a/test/CodeGen/X86/simple-zext.ll b/test/CodeGen/X86/simple-zext.ll
new file mode 100644 (file)
index 0000000..ccd8292
--- /dev/null
+++ b/test/CodeGen/X86/simple-zext.ll
@@ -0,0 +1,16 @@
+; RUN: llc -mtriple=x86_64-apple-darwin < %s| FileCheck %s
+
+; A bug in DAGCombiner prevented it forming a zextload in this simple case
+; because it counted both the chain user and the real user against the
+; profitability total.
+
+define void @load_zext(i32* nocapture %p){
+entry:
+  %0 = load i32* %p, align 4
+  %and = and i32 %0, 255
+  tail call void @use(i32 %and)
+  ret void
+; CHECK: movzbl ({{%r[a-z]+}}), {{%e[a-z]+}}
+}
+
+declare void @use(i32)