When computing the demanded bits of Load SDNodes, make sure that we are looking at the loaded-value operand and not the ptr result (in case of pre-inc loads).

rdar://13348420



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177596 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 51 insertions, 12 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 35707e86ce..64244313a3 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1917,7 +1917,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, APInt &KnownZero,
   }
   case ISD::LOAD: {
     LoadSDNode *LD = cast<LoadSDNode>(Op);
-    if (ISD::isZEXTLoad(Op.getNode())) {
+    // If this is a ZEXTLoad and we are looking at the loaded value.
+    if (ISD::isZEXTLoad(Op.getNode()) && Op.getResNo() == 0) {
       EVT VT = LD->getMemoryVT();
       unsigned MemBits = VT.getScalarType().getSizeInBits();
       KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - MemBits);
@@ -2287,17 +2288,20 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
     break;
   }
 
-  // Handle LOADX separately here. EXTLOAD case will fallthrough.
-  if (LoadSDNode *LD = dyn_cast<LoadSDNode>(Op)) {
-    unsigned ExtType = LD->getExtensionType();
-    switch (ExtType) {
-    default: break;
-    case ISD::SEXTLOAD:    // '17' bits known
-      Tmp = LD->getMemoryVT().getScalarType().getSizeInBits();
-      return VTBits-Tmp+1;
-    case ISD::ZEXTLOAD:    // '16' bits known
-      Tmp = LD->getMemoryVT().getScalarType().getSizeInBits();
-      return VTBits-Tmp;
+  // If we are looking at the loaded value of the SDNode.
+  if (Op.getResNo() == 0) {
+    // Handle LOADX separately here. EXTLOAD case will fallthrough.
+    if (LoadSDNode *LD = dyn_cast<LoadSDNode>(Op)) {
+      unsigned ExtType = LD->getExtensionType();
+      switch (ExtType) {
+        default: break;
+        case ISD::SEXTLOAD:    // '17' bits known
+          Tmp = LD->getMemoryVT().getScalarType().getSizeInBits();
+          return VTBits-Tmp+1;
+        case ISD::ZEXTLOAD:    // '16' bits known
+          Tmp = LD->getMemoryVT().getScalarType().getSizeInBits();
+          return VTBits-Tmp;
+      }
     }
   }
 
diff --git a/test/CodeGen/ARM/zextload_demandedbits.ll b/test/CodeGen/ARM/zextload_demandedbits.ll
new file mode 100644
index 0000000000..3d3269cae2
--- /dev/null
+++ b/test/CodeGen/ARM/zextload_demandedbits.ll
@@ -0,0 +1,35 @@
+; RUN: llc < %s -march=arm -mtriple="thumbv7-apple-ios3.0.0" | FileCheck %s
+
+target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:32:64-v128:32:128-a0:0:32-n32-S32"
+
+%struct.eggs = type { %struct.spam, i16 }
+%struct.spam = type { [3 x i32] }
+%struct.barney = type { [2 x i32], [2 x i32] }
+
+; Make sure that the sext op does not get lost due to ComputeMaskedBits.
+; CHECK: quux
+; CHECK: lsl
+; CHECK: asr
+; CHECK: bl
+; CHECK: pop
+define void @quux(%struct.eggs* %arg) {
+bb:
+  %tmp1 = getelementptr inbounds %struct.eggs* %arg, i32 0, i32 1
+  %0 = load i16* %tmp1, align 2
+  %tobool = icmp eq i16 %0, 0
+  br i1 %tobool, label %bb16, label %bb3
+
+bb3:                                              ; preds = %bb
+  %tmp4 = bitcast i16* %tmp1 to i8*
+  %tmp5 = ptrtoint i16* %tmp1 to i32
+  %tmp6 = shl i32 %tmp5, 20
+  %tmp7 = ashr exact i32 %tmp6, 20
+  %tmp14 = getelementptr inbounds %struct.barney* undef, i32 %tmp7
+  %tmp15 = tail call i32 @widget(%struct.barney* %tmp14, i8* %tmp4, i32 %tmp7)
+  br label %bb16
+
+bb16:                                             ; preds = %bb3, %bb
+  ret void
+}
+
+declare i32 @widget(%struct.barney*, i8*, i32)