DAG: Preserve more flags when expanding gep (llvm#110815)

This allows selecting the addressing mode for stack instructions
in cases where we need to prove the sign bit is zero.

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -4386,34 +4386,50 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
       // it.
       IdxN = DAG.getSExtOrTrunc(IdxN, dl, N.getValueType());
 
+      SDNodeFlags ScaleFlags;
+      // The multiplication of an index by the type size does not wrap the
+      // pointer index type in a signed sense (mul nsw).
+      ScaleFlags.setNoSignedWrap(NW.hasNoUnsignedSignedWrap());
+
+      // The multiplication of an index by the type size does not wrap the
+      // pointer index type in an unsigned sense (mul nuw).
+      ScaleFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());
+
       if (ElementScalable) {
         EVT VScaleTy = N.getValueType().getScalarType();
         SDValue VScale = DAG.getNode(
             ISD::VSCALE, dl, VScaleTy,
             DAG.getConstant(ElementMul.getZExtValue(), dl, VScaleTy));
         if (IsVectorGEP)
           VScale = DAG.getSplatVector(N.getValueType(), dl, VScale);
-        IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, VScale);
+        IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, VScale,
+                           ScaleFlags);
       } else {
         // If this is a multiply by a power of two, turn it into a shl
         // immediately.  This is a very common case.
         if (ElementMul != 1) {
           if (ElementMul.isPowerOf2()) {
             unsigned Amt = ElementMul.logBase2();
-            IdxN = DAG.getNode(ISD::SHL, dl,
-                               N.getValueType(), IdxN,
-                               DAG.getConstant(Amt, dl, IdxN.getValueType()));
+            IdxN = DAG.getNode(ISD::SHL, dl, N.getValueType(), IdxN,
+                               DAG.getConstant(Amt, dl, IdxN.getValueType()),
+                               ScaleFlags);
           } else {
             SDValue Scale = DAG.getConstant(ElementMul.getZExtValue(), dl,
                                             IdxN.getValueType());
-            IdxN = DAG.getNode(ISD::MUL, dl,
-                               N.getValueType(), IdxN, Scale);
+            IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, Scale,
+                               ScaleFlags);
           }
         }
       }
 
-      N = DAG.getNode(ISD::ADD, dl,
-                      N.getValueType(), N, IdxN);
+      // The successive addition of the current address, truncated to the
+      // pointer index type and interpreted as an unsigned number, and each
+      // offset, also interpreted as an unsigned number, does not wrap the
+      // pointer index type (add nuw).
+      SDNodeFlags AddFlags;
+      AddFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());
+
+      N = DAG.getNode(ISD::ADD, dl, N.getValueType(), N, IdxN, AddFlags);
     }
   }
 

llvm/test/DebugInfo/Sparc/pointer-add-unknown-offset-debug-info.ll

@@ -12,7 +12,7 @@ define void @pointer_add_unknown_offset(ptr %base, i32 %offset) !dbg !7 {
   ; CHECK-NEXT:   [[COPY:%[0-9]+]]:i64regs = COPY $i1
   ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:i64regs = COPY $i0
   ; CHECK-NEXT:   [[SRAri:%[0-9]+]]:i64regs = SRAri [[COPY]], 0
-  ; CHECK-NEXT:   [[SLLXri:%[0-9]+]]:i64regs = SLLXri killed [[SRAri]], 2
+  ; CHECK-NEXT:   [[SLLXri:%[0-9]+]]:i64regs = nsw SLLXri killed [[SRAri]], 2
   ; CHECK-NEXT:   DBG_VALUE_LIST !13, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
   ; CHECK-NEXT:   DBG_VALUE_LIST !14, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_plus_uconst, 3, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
   ; CHECK-NEXT:   DBG_VALUE_LIST !15, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 2, DW_OP_plus, DW_OP_LLVM_arg, 1, DW_OP_LLVM_arg, 3, DW_OP_plus, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[COPY1]], [[SLLXri]], [[SLLXri]], debug-location !16