[DAGCombine] Fold overlapping constant stores

Fold a smaller constant store into larger constant stores immediately
preceeding it.

Reviewers: rnk, courbet

Subscribers: javed.absar, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58468

llvm-svn: 354676

llvm/include/llvm/CodeGen/SelectionDAGAddressAnalysis.h

@@ -63,7 +63,13 @@ public:
   // Returns true if `Other` (with size `OtherSize`) can be proven to be fully
   // contained in `*this` (with size `Size`).
   bool contains(int64_t Size, const BaseIndexOffset &Other, int64_t OtherSize,
-                const SelectionDAG &DAG) const;
+                const SelectionDAG &DAG) const {
+    int64_t Offset;
+    return contains(Size, Other, OtherSize, DAG, Offset);
+  }
+
+  bool contains(int64_t Size, const BaseIndexOffset &Other, int64_t OtherSize,
+                const SelectionDAG &DAG, int64_t &Offset) const;
 
   // Returns true `BasePtr0` and `BasePtr1` can be proven to alias/not alias, in
   // which case `IsAlias` is set to true/false.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -15437,6 +15437,32 @@ SDValue DAGCombiner::visitSTORE(SDNode *N) {
           CombineTo(ST1, ST1->getChain());
           return SDValue();
         }
+
+        // If ST stores to a subset of preceeding store's write set, we may be
+        // able to fold ST's value into the preceeding stored value. As we know
+        // the other uses of ST1's chain are unconcerned with ST, this folding
+        // will not affect those nodes.
+        int64_t Offset;
+        if (ChainBase.contains(ChainByteSize, STBase, STByteSize, DAG,
+                               Offset)) {
+          SDValue ChainValue = ST1->getValue();
+          if (auto *C1 = dyn_cast<ConstantSDNode>(ChainValue)) {
+            if (auto *C = dyn_cast<ConstantSDNode>(Value)) {
+              APInt Val = C1->getAPIntValue();
+              APInt InsertVal = C->getAPIntValue().zextOrTrunc(STByteSize * 8);
+              if (DAG.getDataLayout().isBigEndian())
+                Offset = ChainByteSize - 1 - Offset;
+              Val.insertBits(InsertVal, Offset * 8);
+              SDValue NewSDVal =
+                  DAG.getConstant(Val, SDLoc(C), ChainValue.getValueType(),
+                                  C1->isTargetOpcode(), C1->isOpaque());
+              SDNode *NewST1 = DAG.UpdateNodeOperands(
+                  ST1, ST1->getChain(), NewSDVal, ST1->getOperand(2),
+                  ST1->getOperand(3));
+              return CombineTo(ST, SDValue(NewST1, 0));
+            }
+          }
+        } // End ST subset of ST1 case.
       }
     }
   }

llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp

@@ -136,9 +136,8 @@ bool BaseIndexOffset::computeAliasing(const BaseIndexOffset &BasePtr0,
 }
 
 bool BaseIndexOffset::contains(int64_t Size, const BaseIndexOffset &Other,
-                               int64_t OtherSize,
-                               const SelectionDAG &DAG) const {
-  int64_t Offset;
+                               int64_t OtherSize, const SelectionDAG &DAG,
+                               int64_t &Offset) const {
   if (!equalBaseIndex(Other, DAG, Offset))
     return false;
   if (Offset >= 0) {

llvm/test/CodeGen/AArch64/ldst-paired-aliasing.ll

@@ -11,8 +11,8 @@ define i32 @main() local_unnamed_addr #1 {
 ; Make sure the stores happen in the correct order (the exact instructions could change).
 ; CHECK-LABEL: main:
 
-; CHECK: str xzr, [sp, #80]
-; CHECK: str w9, [sp, #80]
+; CHECK: orr w9, wzr, #0x1
+; CHECK: str x9, [sp, #80]
 ; CHECK: stp q0, q0, [sp, #48]
 ; CHECK: ldr w8, [sp, #48]
 

llvm/test/CodeGen/PowerPC/constant-combines.ll

@@ -5,18 +5,15 @@
 define void @fold_constant_stores_loaddr(i8* %i8_ptr) {
 ; BE-LABEL: fold_constant_stores_loaddr:
 ; BE:       # %bb.0: # %entry
-; BE-NEXT:    li 4, 0
+; BE-NEXT:    li 4, 85
+; BE-NEXT:    sldi 4, 4, 57
 ; BE-NEXT:    std 4, 0(3)
-; BE-NEXT:    li 4, -86
-; BE-NEXT:    stb 4, 0(3)
 ; BE-NEXT:    blr
 ;
 ; LE-LABEL: fold_constant_stores_loaddr:
 ; LE:       # %bb.0: # %entry
-; LE-NEXT:    li 4, 0
-; LE-NEXT:    li 5, -86
+; LE-NEXT:    li 4, 170
 ; LE-NEXT:    std 4, 0(3)
-; LE-NEXT:    stb 5, 0(3)
 ; LE-NEXT:    blr
 entry:
   %i64_ptr = bitcast i8* %i8_ptr to i64*
@@ -29,18 +26,15 @@ entry:
 define void @fold_constant_stores_hiaddr(i8* %i8_ptr) {
 ; BE-LABEL: fold_constant_stores_hiaddr:
 ; BE:       # %bb.0: # %entry
-; BE-NEXT:    li 4, 0
+; BE-NEXT:    li 4, 85
+; BE-NEXT:    sldi 4, 4, 57
 ; BE-NEXT:    std 4, 0(3)
-; BE-NEXT:    li 4, -86
-; BE-NEXT:    stb 4, 0(3)
 ; BE-NEXT:    blr
 ;
 ; LE-LABEL: fold_constant_stores_hiaddr:
 ; LE:       # %bb.0: # %entry
-; LE-NEXT:    li 4, 0
-; LE-NEXT:    li 5, -86
+; LE-NEXT:    li 4, 170
 ; LE-NEXT:    std 4, 0(3)
-; LE-NEXT:    stb 5, 0(3)
 ; LE-NEXT:    blr
 entry:
   %i64_ptr = bitcast i8* %i8_ptr to i64*

llvm/test/CodeGen/X86/stores-merging.ll

@@ -26,9 +26,8 @@ define void @redundant_stores_merging() {
 define void @redundant_stores_merging_reverse() {
 ; CHECK-LABEL: redundant_stores_merging_reverse:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movabsq $528280977409, %rax # imm = 0x7B00000001
+; CHECK-NEXT:    movabsq $1958505086977, %rax # imm = 0x1C800000001
 ; CHECK-NEXT:    movq %rax, e+{{.*}}(%rip)
-; CHECK-NEXT:    movl $456, e+{{.*}}(%rip) # imm = 0x1C8
 ; CHECK-NEXT:    retq
   store i32 123, i32* getelementptr inbounds (%structTy, %structTy* @e, i64 0, i32 2), align 4
   store i32 456, i32* getelementptr inbounds (%structTy, %structTy* @e, i64 0, i32 2), align 4