[InstCombine] Support zext nneg in gep of sext add fold

Add m_NNegZext() and m_SExtLike() matchers to make doing these kinds
of changes simpler in the future.

Author: nikic

llvm/include/llvm/IR/PatternMatch.h

@@ -1656,6 +1656,19 @@ template <typename Op_t> struct PtrToIntSameSize_match {
   }
 };
 
+template <typename Op_t> struct NNegZExt_match {
+  Op_t Op;
+
+  NNegZExt_match(const Op_t &OpMatch) : Op(OpMatch) {}
+
+  template <typename OpTy> bool match(OpTy *V) {
+    if (auto *I = dyn_cast<Instruction>(V))
+      return I->getOpcode() == Instruction::ZExt && I->hasNonNeg() &&
+             Op.match(I->getOperand(0));
+    return false;
+  }
+};
+
 /// Matches BitCast.
 template <typename OpTy>
 inline CastOperator_match<OpTy, Instruction::BitCast>
@@ -1707,6 +1720,11 @@ inline CastInst_match<OpTy, Instruction::ZExt> m_ZExt(const OpTy &Op) {
   return CastInst_match<OpTy, Instruction::ZExt>(Op);
 }
 
+template <typename OpTy>
+inline NNegZExt_match<OpTy> m_NNegZExt(const OpTy &Op) {
+  return NNegZExt_match<OpTy>(Op);
+}
+
 template <typename OpTy>
 inline match_combine_or<CastInst_match<OpTy, Instruction::ZExt>, OpTy>
 m_ZExtOrSelf(const OpTy &Op) {
@@ -1719,6 +1737,14 @@ m_SExtOrSelf(const OpTy &Op) {
   return m_CombineOr(m_SExt(Op), Op);
 }
 
+/// Match either "sext" or "zext nneg".
+template <typename OpTy>
+inline match_combine_or<CastInst_match<OpTy, Instruction::SExt>,
+                        NNegZExt_match<OpTy>>
+m_SExtLike(const OpTy &Op) {
+  return m_CombineOr(m_SExt(Op), m_NNegZExt(Op));
+}
+
 template <typename OpTy>
 inline match_combine_or<CastInst_match<OpTy, Instruction::ZExt>,
                         CastInst_match<OpTy, Instruction::SExt>>

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -2516,7 +2516,7 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
                                        Idx2);
     }
     ConstantInt *C;
-    if (match(GEP.getOperand(1), m_OneUse(m_SExt(m_OneUse(m_NSWAdd(
+    if (match(GEP.getOperand(1), m_OneUse(m_SExtLike(m_OneUse(m_NSWAdd(
                                      m_Value(Idx1), m_ConstantInt(C))))))) {
       // %add = add nsw i32 %idx1, idx2
       // %sidx = sext i32 %add to i64

llvm/test/Transforms/InstCombine/array.ll

@@ -77,9 +77,9 @@ define void @test_zext_nneg(ptr %ptr, i32 %a, i32 %b) {
 ; CHECK-LABEL: define void @test_zext_nneg(
 ; CHECK-SAME: ptr [[PTR:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 10
-; CHECK-NEXT:    [[IDX:%.*]] = zext nneg i32 [[ADD]] to i64
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[PTR]], i64 [[IDX]]
+; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[A]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[TMP0]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 10
 ; CHECK-NEXT:    store i32 [[B]], ptr [[GEP]], align 4
 ; CHECK-NEXT:    ret void
 ;