[llvm] r346654 - [DAGCombiner] Fix load-store forwarding of indexed loads.

[Nirav Dave via llvm-commits]

Author: niravd
Date: Mon Nov 12 06:05:40 2018
New Revision: 346654

URL: http://llvm.org/viewvc/llvm-project?rev=346654&view=rev
Log:
[DAGCombiner] Fix load-store forwarding of indexed loads.

Summary:
Handle extra output from index loads in cases where we wish to
forward a load value directly from a preceeding store.

Fixes PR39571.

Reviewers: peter.smith, rengolin

Subscribers: javed.absar, hiraditya, arphaman, llvm-commits

Differential Revision: https://reviews.llvm.org/D54265

Added:
    llvm/trunk/test/CodeGen/ARM/pr39571.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=346654&r1=346653&r2=346654&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Nov 12 06:05:40 2018
@@ -12866,6 +12866,20 @@ SDValue DAGCombiner::ForwardStoreValueTo
   bool STCoversLD =
       (Offset >= 0) &&
       (Offset * 8 + LDMemType.getSizeInBits() <= STMemType.getSizeInBits());
+
+  auto ReplaceLd = [&](LoadSDNode *LD, SDValue Val, SDValue Chain) -> SDValue {
+    if (LD->isIndexed()) {
+      bool IsSub = (LD->getAddressingMode() == ISD::PRE_DEC ||
+                    LD->getAddressingMode() == ISD::POST_DEC);
+      unsigned Opc = IsSub ? ISD::SUB : ISD::ADD;
+      SDValue Idx = DAG.getNode(Opc, SDLoc(LD), LD->getOperand(1).getValueType(),
+                             LD->getOperand(1), LD->getOperand(2));
+      SDValue Ops[] = {Val, Idx, Chain};
+      return CombineTo(LD, Ops, 3);
+    }
+    return CombineTo(LD, Val, Chain);
+  };
+
   if (!STCoversLD)
     return SDValue();
 
@@ -12873,7 +12887,7 @@ SDValue DAGCombiner::ForwardStoreValueTo
   if (Offset == 0 && LDType == STType && STMemType == LDMemType) {
     // Simple case: Direct non-truncating forwarding
     if (LDType.getSizeInBits() == LDMemType.getSizeInBits())
-      return CombineTo(LD, ST->getValue(), Chain);
+      return ReplaceLd(LD, ST->getValue(), Chain);
     // Can we model the truncate and extension with an and mask?
     if (STType.isInteger() && LDMemType.isInteger() && !STType.isVector() &&
         !LDMemType.isVector() && LD->getExtensionType() != ISD::SEXTLOAD) {
@@ -12883,7 +12897,7 @@ SDValue DAGCombiner::ForwardStoreValueTo
                                                STMemType.getSizeInBits()),
                           SDLoc(ST), STType);
       auto Val = DAG.getNode(ISD::AND, SDLoc(LD), LDType, ST->getValue(), Mask);
-      return CombineTo(LD, Val, Chain);
+      return ReplaceLd(LD, Val, Chain);
     }
   }
 
@@ -12908,7 +12922,7 @@ SDValue DAGCombiner::ForwardStoreValueTo
     }
     if (!extendLoadedValueToExtension(LD, Val))
       continue;
-    return CombineTo(LD, Val, Chain);
+    return ReplaceLd(LD, Val, Chain);
   } while (false);
 
   // On failure, cleanup dead nodes we may have created.

Added: llvm/trunk/test/CodeGen/ARM/pr39571.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/pr39571.ll?rev=346654&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/pr39571.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/pr39571.ll Mon Nov 12 06:05:40 2018
@@ -0,0 +1,33 @@
+; RUN: llc < %s -mtriple armv4t-unknown-linux-gnueabi -mattr=+strict-align
+
+; Avoid crash from forwarding indexed-loads back to store.
+%struct.anon = type { %struct.ma*, %struct.mb }
+%struct.ma = type { i8 }
+%struct.mb = type { i8, i8 }
+%struct.anon.0 = type { %struct.anon.1 }
+%struct.anon.1 = type { %struct.ds }
+%struct.ds = type <{ i8, %union.ie }>
+%union.ie = type { %struct.ib }
+%struct.ib = type { i8, i8, i16 }
+
+ at a = common dso_local local_unnamed_addr global %struct.anon* null, align 4
+ at b = common dso_local local_unnamed_addr global %struct.anon.0 zeroinitializer, align 1
+
+; Function Attrs: norecurse nounwind
+define dso_local void @func() local_unnamed_addr {
+entry:
+  %0 = load %struct.anon*, %struct.anon** @a, align 4
+  %ad = getelementptr inbounds %struct.anon, %struct.anon* %0, i32 0, i32 0
+  %1 = load %struct.ma*, %struct.ma** %ad, align 4
+  %c.sroa.0.0..sroa_idx = getelementptr inbounds %struct.ma, %struct.ma* %1, i32 0, i32 0
+  %c.sroa.0.0.copyload = load i8, i8* %c.sroa.0.0..sroa_idx, align 1
+  %cb = getelementptr inbounds %struct.anon, %struct.anon* %0, i32 0, i32 1
+  %band = getelementptr inbounds %struct.anon, %struct.anon* %0, i32 0, i32 1, i32 1
+  store i8 %c.sroa.0.0.copyload, i8* %band, align 4
+  store i8 6, i8* getelementptr inbounds (%struct.anon.0, %struct.anon.0* @b, i32 0, i32 0, i32 0, i32 1, i32 0, i32 0), align 1
+  store i8 2, i8* getelementptr inbounds (%struct.anon.0, %struct.anon.0* @b, i32 0, i32 0, i32 0, i32 1, i32 0, i32 1), align 1
+  %2 = bitcast %struct.mb* %cb to i32*
+  %3 = load i32, i32* bitcast (i8* getelementptr inbounds (%struct.anon.0, %struct.anon.0* @b, i32 0, i32 0, i32 0, i32 1, i32 0, i32 0) to i32*), align 1
+  store i32 %3, i32* %2, align 1
+  ret void
+}