Fixup: Also handle "nusw nuw"

Author: bjope

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -3119,17 +3119,14 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   // These rewrites is trying to preserve inbounds/nuw attributes. So we want to
   // do this after having tried to derive "nuw" above.
   if (GEP.getNumIndices() == 1) {
+    // Given (gep p, x+y) we want to determine the common nowrap flags for both
+    // gep if transforming into (gep (gep p, x), y).
     auto GetPreservedNoWrapFlags = [&](bool AddIsNUW) {
-      // Preserve "inbounds nuw" if the original gep is "inbounds nuw", and the
-      // add is "nuw". Preserve "nuw" if the original gep is "nuw", and the add
-      // is "nuw".
-      GEPNoWrapFlags Flags = GEPNoWrapFlags::none();
-      if (GEP.hasNoUnsignedWrap() && AddIsNUW) {
-        Flags |= GEPNoWrapFlags::noUnsignedWrap();
-        if (GEP.isInBounds())
-          Flags |= GEPNoWrapFlags::inBounds();
-      }
-      return Flags;
+      // We can preserve both "inbounds nuw", "nusw nuw" and "nuw" if we know
+      // that x + y does not have unsigned wrap.
+      if (GEP.hasNoUnsignedWrap() && AddIsNUW)
+        return GEP.getNoWrapFlags();
+      return GEPNoWrapFlags::none();
     };
 
     // Try to replace ADD + GEP with GEP + GEP.

llvm/test/Transforms/InstCombine/array.ll

@@ -134,12 +134,11 @@ define ptr @gep_inbounds_add_nuw(ptr %ptr, i64 %a, i64 %b) {
   ret ptr %gep
 }
 
-; FIXME: Preserve "nusw nuw".
 define ptr @gep_inbounds_add_nusw_nuw(ptr %ptr, i64 %a, i64 %b) {
 ; CHECK-LABEL: define ptr @gep_inbounds_add_nusw_nuw(
 ; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr nuw i32, ptr [[PTR]], i64 [[A]]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nuw i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr nusw nuw i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nusw nuw i32, ptr [[TMP1]], i64 [[B]]
 ; CHECK-NEXT:    ret ptr [[GEP]]
 ;
   %add = add nuw i64 %a, %b